CMS PAPER CFT-09-022
FERMILAB-PUB-10-153-CMS
CMS Paper
arXiv:0911.4893v2 [physics.ins-det] 16 Dec 2009
2009/12/16
Performance of the CMS Drift-Tube Chamber Local Trigger
with Cosmic Rays
The CMS Collaboration∗
Abstract
The performance of the Local Trigger based on the drift-tube system of the CMS experiment has been studied using muons from cosmic ray events collected during the
commissioning of the detector in 2008. The properties of the system are extensively
tested and compared with the simulation. The effect of the random arrival time of the
cosmic rays on the trigger performance is reported, and the results are compared with
the design expectations for proton-proton collisions and with previous measurements
obtained with muon beams.
∗ See
Appendix A for the list of collaboration members
1
1 Introduction
The primary goal of the Compact Muon Solenoid (CMS) experiment [1] is to explore particle
physics at the TeV energy scale exploiting the proton-proton collisions delivered by the Large
Hadron Collider (LHC) [2]. During October-November 2008 CMS conducted a month-long
data taking exercise with the goal of commissioning the experiment for extended operation [3].
The experiment recorded 270 million cosmic ray triggered events with the solenoid at its nominal axial field strength of 3.8 T. Prior to this, and during the final installation phase of the
experiment, a series of week-long commissioning exercises to record cosmic ray events took
place from May to September 2008, without magnetic field. Over 300 million cosmic ray triggers were accumulated during this data taking period. The drift-tube muon system of the
detector continuously provided the trigger to the experiment and enabled muon track reconstruction. The drift-tube Local Trigger is the component of the trigger system that provides the
information to reconstruct muon trigger candidates in the drift-tube system.
This paper describes the performance of the drift-tube Local Trigger system determined from
data collected in this data taking period. Results include measurements of the system efficiency,
the performance of the bunch crossing identification, the position and angular resolution of the
muon-trigger candidate, and the false dimuon trigger rate. The trigger data are also compared
with software emulation. Such studies test the reliability of the system and improve the understanding of the muon trigger performance in preparation for LHC operation. The trigger
system design is optimized for muons produced in bunched-beam collisions. The random arrival time of the cosmic rays degrades the average performance compared to the expectations
for proton-proton collisions. However, results for particles traversing the detector with the
proper timing show that the system will perform as required for muons produced at the LHC.
2 The Experimental Apparatus
The central feature of the CMS apparatus is a superconducting solenoid, of 6 m internal diameter, providing a field of 3.8 T. Within the field volume are the silicon pixel and strip tracker,
the crystal electromagnetic calorimeter (ECAL), and the brass/scintillator hadron calorimeter
(HCAL). Muons are measured in gas-ionization detectors embedded in the steel return yoke. In
addition to the barrel and endcap detectors, CMS has extensive forward calorimetry. A detailed
description of the CMS experiment can be found in Ref. [1].
CMS uses a right-handed coordinate system, with the origin at the nominal collision point,
the x-axis pointing to the center of the LHC, the y-axis pointing up (perpendicular to the LHC
plane), and the z-axis along the anticlockwise-beam direction. The polar angle, θ, is measured
from the positive z-axis and the azimuthal angle, φ, is measured in the x-y plane.
The CMS experiment has a two-level trigger system: the Level-1 Trigger and the High Level
Trigger. The Level-1 Trigger is composed of custom hardware processors and it uses information from the calorimeters and muon detectors to select the events with a constant latency of
about 3.5 µs. The High Level Trigger processor farm further decreases the event rate from a
maximum input rate of 100 kHz to an event recording rate of approximately 100 Hz [4, 5].
The muon detection system covers the pseudorapidity range |η | < 2.4 with detection planes
based on three different technologies: drift tubes (DT), cathode strip chambers (CSC), and resistive plate chambers (RPC) [6]. The DT system is located in the barrel part of the detector,
extending over the range |η | < 1.3, whereas CSCs are used in the endcaps, in the region
0.8 < |η | < 2.4. The RPC system covers the region |η | < 1.6. Combining the measured
2
2
The Experimental Apparatus
Figure 1: Left: schematic view of one of the five wheels of the muon barrel system of the CMS
experiment, in the x-y plane. Right: the five wheels are visible in the longitudinal view of the
CMS detector.
tracks from charged particles in the muon system with those measured in the silicon tracker
results in a transverse momentum resolution between 1 and 5 % for transverse momenta up
to 1 TeV/c [7]. The muon detector also provides a highly efficient muon trigger. The usage
of RPCs and DTs in the barrel, and RPCs and CSCs in the endcaps, makes the system robust
and redundant. Both the DT and CSC detectors perform muon tracking and participate in the
Level-1 muon trigger, independently of the RPCs.
2.1
The Drift-Tube Muon System
The DT system consists of 240 muon chambers. Figure 1 shows how the muon chambers are
arranged in 12 sectors with four station types in each of the five wheels of the CMS barrel. The
four station types are called MB1, MB2, MB3, and MB4 from inside to outside, where MB stands
for Muon Barrel. Although the chambers of station type MB4 in sectors 4 and 10 are physically
divided in two parts, in this paper they are considered as a single unit. In each chamber eight
layers of DT cells with wires parallel to the beam direction are arranged in two ”superlayers”
of four layers each, devoted to trigger and position measurements in the x-y plane. With the
exception of type MB4, all chambers are equipped with an extra ”superlayer” of four layers
to perform measurements along the z coordinate using DT cells with wires orthogonal to the
beam direction.
Chambers are equipped with Time to Digital Converter (TDC) units, which measure the drift
time in each cell, as well as with dedicated electronics to perform the Level-1 trigger algorithm.
For tracking purposes, the signals recorded by the TDC units are converted to position coordinates (called “hits”) using the space-time relation determined with the knowledge of the drift
velocity. In each chamber, track segments are reconstructed using a linear fit to the hits, and are
used for the offline reconstruction of the muon tracks [8]. For triggering purposes, the DT Local Trigger algorithm searches for aligned hits, called trigger segments, in each chamber, using
dedicated electronics and algorithms that are independent of the TDC track fitting.
3
2.2 The Drift-Tube Local Trigger
2.2
The Drift-Tube Local Trigger
The DT Local Trigger system and its performance are described in detail in Refs. [4, 9, 10].
Dedicated adjustments to the configuration of the DT trigger were needed to provide high
efficiency for cosmic ray muons, which have a different origin, direction, and timing compared
to muons from proton-proton collisions [11]. In this section, only the main functionalities and
characteristics are summarized. The trigger segments are found separately in the transverse
plane x-y (called φ view) and in the plane that contains the z direction (called θ view).
The maximum drift time in the DT system is almost 400 ns, which is much longer than the 25 ns
interval that separates two consecutive collisions. Therefore, the trigger system must first associate each trigger segment to the correct bunch crossing (BX). For each BX the trigger system
provides up to two trigger segments per chamber in the φ view, and one in the θ view. In the φ
view, each trigger segment is associated with the following quantities: the BX, at which the corresponding muon candidate was produced; the position and direction in the local coordinate
system of the chamber; a quality word describing how many aligned DT hits were found; and
a bit flagging the segment as a first or second candidate, ordered according to their assigned
quality, for that BX. One set of such quantities is called a “trigger primitive”.
BTI
m
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Figure 2: The main components of the DT Local Trigger in the φ view of a muon chamber. The
BTIs detect hit alignments within each superlayer, the TRACOs search for a proper matching
between superlayers, and the Trigger Server selects the best two candidates in the chamber and
applies a ghost-suppression algorithm.
Trigger segments in the θ view are issued if there are three or four aligned hits in the corresponding superlayer. The θ trigger primitive includes the assigned BX, a word defining the
4
2
The Experimental Apparatus
location in the chamber, and its quality word. During LHC operation, the system in the θ
view will be configured to accept only trigger segments pointing to the interaction region. This
condition was not applied for data taking with cosmic rays.
The trigger algorithm that provides the trigger primitives in the φ view works in three logical
steps that are sketched in Fig. 2. For every BX, the Bunch and Track Identifiers (BTIs) search
for track segment candidates made of three or four aligned DT hits within a superlayer. Each
candidate is processed by the Track Correlators (TRACOs), which search for a proper angular
matching between the candidates from the two superlayers in each chamber. TRACO candidates are then sent to the Trigger Server, which performs a ghost-suppression mechanism and
then selects for each BX the two trigger primitives with highest quality. The quality is defined
according to the number of aligned hits in the trigger segment. An alignment of hits in a superlayer is labeled “High” (H) or “Low” (L) if it includes four or three DT hits, respectively. The
quality of a trigger segment in the φ view is labeled HH, HL, or LL if a matching (correlation),
both in angle and BX, is found between the segments of the two superlayers. In this case the
trigger segments are called “correlated”. If no correlation is found, and four aligned hits are
detected in the inner (outer) superlayer of the chamber (where inner and outer are defined according to their distance from the center of the CMS detector), the segment quality is labeled
as HI (HO).
The DT Local trigger is designed for triggering on particles produced synchronously with the
bunch crossing signal. One of the effects of the random arrival time of the cosmic muons is the
production of spurious uncorrelated trigger segments with wrong bunch crossing assignment.
Therefore, to reduce the rate of such spurious triggers, the DT Local Trigger was configured
such that the presence of a θ trigger segment was required to accept uncorrelated H-quality
triggers in the φ view. At the LHC, where muons are synchronously produced with the bunch
crossing signal, spurious triggers will be largely suppressed, so that the trigger configuration
will be relaxed to accept also uncorrelated L-quality triggers.
The ghost-suppression mechanism is performed to discard additional trigger candidates attributable to false signals (“ghosts”). The false trigger segments mostly arise from the fact that
adjacent TRACO units share a common group of DT cells, and a hit alignment can be found
twice. The segment selection and ghost-suppression algorithms are flexible and can be configured to match various experimental conditions, such as the presence of groups of noisy or
disconnected DT cells in a chamber.
The position and angle parameters of the trigger segment, named Φ and Φb respectively, are
illustrated in Fig. 3, together with the angle ψ that defines the inclination of the trigger segment
with respect to the direction perpendicular to the chamber plane. The parameter Φ is determined by the position of the trigger segment with respect to the center of the chamber, whereas
the quantity Φb is the angle between the direction of the trigger segment and the straight line
from the interaction point to the segment position.
The data from the four Trigger Server units of every muon sector are sent to the Regional Trigger [12], which independently performs the matching between trigger segments in the φ and θ
views, using two different systems: the Phi Track Finder and the Eta Track Finder, respectively.
In the data analysed for this study the Eta Track Finder was not yet operational. The matching
of segments between chambers is performed by the Phi Track Finder using configurable lookup tables, which define the range, in terms of position and angle, where a valid extrapolation
of a trigger segment from one chamber to another is expected. The Phi Track Finder extrapolation mechanism was not used during the data taking with cosmic ray muons in order to
maximize the geometrical acceptance. The Phi Track Finder processed data within one sector
2.3 The Event Selection
5
Figure 3: Definition of the Φ and Φb parameters provided by the DT Local Trigger, shown for
the outermost muon chamber. The angle ψ represents the inclination of the trigger segment
with respect to the direction perpendicular to the chamber plane. The angle Φ is defined with
respect to the center of the chamber.
or two neighboring sectors, by searching for a signal coincidence in at least two chambers. Up
to four candidates, ordered according to their transverse momenta, are selected and forwarded
to the Global Muon Trigger, where they are combined with muon-trigger candidates from RPCs
and CSCs [4]. During data taking with cosmic rays, a Level-1 trigger rate of about 240 Hz was
passed from the Phi Track Finder to the Global Muon Trigger.
The DT Local Trigger signals from the various chambers must arrive synchronously at the Regional Trigger, and a dedicated synchronization procedure was developed for triggering with
cosmic rays. The time taken by the particles traversing the detector from top to bottom depends
on the track incident angle, and is approximately 50 ns for cosmic muons traversing both sectors 4 and 10. To synchronize the DT trigger system, the latency of the trigger signals of the
chambers in the upper sectors was increased up to a maximum delay time of 50 ns, which corresponds to two bunch crossings. The delays for each individual chamber were obtained with
data from dedicated synchronization runs by examining the bunch crossing distribution of the
trigger segments from different detector regions with respect to a reference sector. This allowed
the synchronization of all chambers to be within a fraction of a bunch crossing, regardless of
the direction and the position of the incoming particle.
2.3
The Event Selection
Unless explicitly mentioned, the results shown in this paper are obtained using data collected
with the CMS solenoid operating at 3.8 T. The data were collected in periods of stable DT
operation. No requirements on the status of the other CMS detectors and their participation
in the data taking are applied to the event selection, except when explicitly mentioned. The
sample used for the analysis corresponds to approximately 10 million events. This is large
enough to make statistical uncertainties negligible for the measurements performed.
The trigger and data acquisition are synchronized with a 40 MHz signal replicating the LHC BX
6
3
Performance of the DT Local Trigger
frequency. The Level-1 Trigger signal requires the coincidence, at the same BX, of at least two
trigger primitives from two chambers of the same sector or of two adjacent sectors. To avoid
any bias in the event selection, it is required that at least two chambers distinct from the one
under investigation have provided trigger primitives. This guarantees that the event is selected
by the Level-1 Trigger independently of the chamber under investigation. To measure the trigger efficiency in a chamber, the presence of a local track segment reconstructed with at least 7
out of 8 TDC hits in the φ view is also required. The radial angle of the track segment must be
in the range |ψ| < 30◦ , to stay within the TRACO angular acceptance. To remove events with
two or more muon tracks in the same chamber, at most 12 TDC hits are allowed in the φ view
of the chamber under investigation. The efficiency of the DT Local Trigger in the chamber is
defined as the fraction of the selected events that have an associated trigger primitive in the
chamber, in the same or in any of the two adjacent BXs. This definition of efficiency allows the
measurement of the effective net trigger capability, excluding the geometrical acceptance and
the DT cell efficiency. This event selection is employed for the analysis described in this paper,
except where explicitly stated otherwise.
3 Performance of the DT Local Trigger
Muons produced in LHC collisions will cross each DT chamber at a well defined time with
respect to the signal of the BX clock, with a jitter of a few nanoseconds, due to the different
path lengths in the magnetic field. The BTI electronics will be properly synchronized with the
arrival time of the particles to perform the best hit alignment [13, 14]. However, cosmic ray
muons traverse the detector at arbitrary times with respect to the 40 MHz signal that simulates
the BX clock. Taking the signal of the BX clock as a time reference, the BTI is configured to detect
hit alignments in the most efficient way in a time range that is about 10 ns wide. Therefore, only
muons arriving within the 10 ns time window will be correctly identified by the trigger, while
outside this time window the efficiency of the BTI to find aligned hits is degraded.
3.1
Trigger Efficiency
To illustrate the effect of the random arrival time of the cosmic rays on the performance measurements presented in this paper, Fig. 4 shows the DT Local Trigger efficiency as a function
of the arrival time of the muon with respect to the global time reference tTrig . The quantity
tTrig represents the value to be subtracted from the time measured by the TDC (called tDigi ) to
correct for the trigger latency and for differences in the propagation time of the signals in the
system. The determination of tTrig is described in Ref. [15], and it is performed by fitting the
position of the rising edge of the tDigi distribution separately in each superlayer. The arrival
time with respect to tTrig is individually computed for every muon and event, by performing
a linear fit to the TDC hits in the chamber. The arrival time is a free parameter of the fit, and
it is determined, event-by-event, as the time shift to be added to tTrig giving the best spatial
resolution for every event by achieving the best track-segment fit [16]. This shift represents the
time offset at which the muon traversed the chamber with respect to the reference time tTrig ,
which is the mean arrival time averaged over many events.
Figure 4 shows that the DT Local Trigger efficiency is not constant as a function of the arrival
time of the particle, in particular for trigger segments of HH quality, but it is maximal and flat
in a region approximately 10 ns wide. To first order, the efficiency has a periodicity of 25 ns,
which is the time difference between two consecutive BXs. As the events selection requires the
time coincidence of trigger segments in at least two chambers, uncertainties in their relative
synchronization, which was typically of the order of a fraction of a BX during the period of
7
Efficiency
3.1 Trigger Efficiency
CMS 2008
1
0.8
0.6
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Any Quality
Correlated
HH
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Figure 4: Efficiency of the DT Local Trigger as a function of the muon arrival time in the chamber, defined with respect to the tTrig time reference. Results for a chamber of type MB1 are
shown as an example, for various types of trigger quality.
data taking, can bias the measured arrival time of the muons, thus resulting in an imperfect
periodicity of the efficiency curve. The time dependence of the efficiency reflects the fact that
the trigger system is optimized for muons arriving in the time range corresponding to the flattop region of Fig. 4. For LHC operation, the trigger timing will be adjusted so that muons
from collisions will traverse the detector within this time range. For the tests with cosmic ray
muons, however, this results in an overall degradation of the average performance of the DT
Local Trigger compared to the expectations for the LHC and the results with bunched-beam
tests, in terms of efficiency, quality of the trigger primitives, and BX identification.
In the 10 ns flat-top region, where the trigger system is well synchronized with the incoming
particles, the DT Local Trigger efficiency is approximately 0.60 for triggers of HH quality, 0.90
for correlated triggers, and 0.97 for any trigger quality. These values are consistent with previous measurements at bunched-beam tests [9, 10], as well as with the technical specifications
required for efficient triggering with particle collisions [4].
The average DT Local Trigger efficiencies obtained using all cosmic ray muons, regardless of
their arrival time with respect to the reference time tTrig , are 0.95 for triggers of any quality, 0.80
for correlated triggers, and 0.48 for triggers of HH quality. These values are lower than the
values reached in the plateau of maximum efficiency shown in Fig. 4, where the performance
of the system is optimal. They have a spread of 0.02 among the chambers, mostly caused by the
different angles of incidence of the cosmic rays on the chambers and by a few malfunctioning
trigger devices. The few chambers with major hardware or read-out problems are not taken
into account in the computation. These problems were fixed during the detector shutdown at
the end of 2008.
The results on the DT Local Trigger efficiency are cross-checked using an independent event
selection that does not explicitly require the presence of DT hits in the chamber under study.
For this purpose, events triggered by the RPCs are selected. In such events, muon tracks are
subsequently reconstructed using the DT hits in the muon barrel and CSC hits in the endcaps.
The tracks are extrapolated along the detector, and required to cross the chamber under study
in its active region, without any requirement on the presence of DT hits in that chamber. The
8
Number of entries
3
Performance of the DT Local Trigger
45
40
CMS 2008
35
30
25
Any Quality
Correlated
MB4 station
20
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Efficiency
Figure 5: Distribution of the DT Local Trigger efficiency in the φ view of the muon chambers,
for events selected by the RPC trigger. Each entry corresponds to one barrel chamber. Results
for any trigger quality and for correlated triggers are shown. The shaded histogram represents
the results for station type MB4, for which only correlated triggers are provided.
chamber is considered efficient if there is a trigger segment in the φ view, in the same or in any
of the two adjacent BXs. In order to remain within the geometrical acceptance of the trigger,
only tracks with an angle of incidence |ψ| < 30◦ were considered. Figure 5 shows the distribution of the DT Local Trigger efficiency measured for these events. Each entry represents one
muon chamber. Results are shown for any trigger quality and for correlated triggers. Results
for station type MB4, for which only correlated triggers are provided, are shown separately.
In contrast to the previously described measurement, this definition of the DT Local Trigger
efficiency includes effects of geometrical acceptance at the edges of the chambers, cell inefficiency, dead channels, and hardware failures. Therefore, the measured values are on average a
few percent lower than the ones previously reported. For triggers of any quality the efficiency
distribution has a maximum at 95 %. Values below 70 % are due to read-out or hardware problems, which have been fixed during the detector shutdown at the end of 2008. For correlated
triggers, the efficiencies below 70 % are related to chambers oriented vertically in the detector
(sectors 1 and 7). In this case, given the angular distribution of cosmic rays, there is a high
probability to fail the correlation between superlayers near the edges of the chambers. In this
detector region the low efficiency is partially recovered if trigger segments of any quality are
accepted, and in this case it reaches values between 80 % and 90 %.
The DT Local Trigger efficiency as a function of the incidence angle |ψ| is also measured, for
trigger segments of any quality. In this case the requirement on the incidence angle of the
track, |ψ| < 30◦ , is removed, and the efficiency value is averaged over all chambers, with the
exclusion of sectors 1 and 7. The results, reported in Fig. 6, are in agreement with previous test
beam measurements [9] and show that the trigger efficiency has a constant plateau for tracks
with inclination up to about 35◦ , and it decreases by a factor of 2 at the maximum BTI angular
acceptance of 45◦ . This corresponds, in the case of LHC collisions, to full trigger efficiency for
tracks with transverse momenta exceeding 3 GeV/c.
9
Efficiency
3.2 Bunch Crossing Identification
1
0.8
0.6
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CMS 2008
0.2
0
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Figure 6: Average DT Local Trigger efficiency in the φ view of the muon chambers for trigger
segments of any quality, as a function of the angle of incidence |ψ| of the muon tracks.
3.2
Bunch Crossing Identification
CMS 2008
H Triggers
10-1
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CMS 2008
LL+HL Triggers
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Fraction of triggers
Fraction of triggers
The performance of the BX identification is measured by comparing the assigned bunch crossing in the chamber under study, called “trigger BX”, with respect to the BX defined by the
coincidence of the other two trigger segments in the same sector, called “expected BX”. The
difference between the “expected BX” and the “trigger BX” is shown in Fig. 7 for different trigger qualities. The data from a chamber of type MB1 in sector 4 are used as an example. The
results are similar for the other chambers in the detector. The events for which the difference
between the “expected BX” and the “trigger BX” is zero have a correct BX identification. The
distributions, normalized to unity, show that, even in the difficult environment of cosmic rays,
triggers of HH quality provide correct BX identification in 82 % of the cases. The distribution
is affected by imperfect synchronization between the chambers during data taking. The distribution is wider for poorer trigger quality. Because of a feature of the BTI system, the events
with badly identified BX mainly populate the left-most part of the distribution for low-quality
triggers, as they are trigger segments with wrong hit alignments that are typically produced
later with respect to the correct BX. Such triggers are significantly suppressed in the case of
quality type HH.
1
CMS 2008
HH Triggers
10-1
10-2
10-3
-4
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Expected BX -Trigger BX
10-4
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Figure 7: Distribution of the difference between the “expected BX” and the observed BX ( “trigger BX”) of the trigger segment, in one chamber of type MB1 in sector 4, for different trigger
qualities. The distributions are normalized to unity.
10
3
Performance of the DT Local Trigger
CMS 2008
Any quality
1600
1400
1200
Number of events
Number of events
In bunched-beam tests the BX identification for trigger segments of quality HH was close to
100 % [9, 10]. In the present analysis, the degraded performance of the BX identification is
explained by the timing characteristics of the cosmic rays already discussed. Events selected
with the optimal arrival time of the muon tracks (as discussed in section 3.1) show that the
BX identification capability for triggers of HH quality approaches 100 %, thus matching the
design expectations for proton-proton collisions. This can be seen in Fig. 8, which shows the
distribution of the arrival time of the muon tracks (in the same chamber used for Fig. 4), for
events with a trigger segment of any quality (left) and for quality type HH (right). The distributions for trigger segments with correct BX assignment (“expected BX” equal to “trigger
BX”) and wrong BX assignment are shown separately. In the region approximately ± 5 ns wide
around zero, where the timing of the trigger system is optimized (as discussed for the results
of Fig. 4), the wrongly timed triggers of any quality contribute only marginally, and they can
be completely neglected in the case of trigger segments of HH quality.
CMS 2008
HH
1000
800
Good BX
Good BX
1000
600
Wrong BX
Wrong BX
800
400
600
400
200
200
0
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0
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Figure 8: Left: distribution of the muon arrival time, for trigger segments of any quality. Right:
distribution of the muon arrival time for trigger segments of HH quality. Events with correct
and wrong BX identification are shown separately. Results for a chamber of type MB1 in sector
4 are shown as an example.
3.3
False Dimuon Trigger Rate
The DT Local Trigger provides up to two trigger segments for any BX in the φ view of each
chamber. This feature was introduced to maximize the trigger efficiency for nearby muons. On
the other hand, a ghost suppression mechanism is implemented to reject false trigger pairs that
originate from a single muon crossing the detector. As the dimuon production rate above any
given transverse momentum threshold is expected to be approximately 1 % of the single muon
rate at the LHC [4], the rate of false Level-1 dimuon triggers must be well below 1 %. With
cosmic rays the fraction of double triggers over single triggers provided in a single chamber
at the same BX, averaged over all the chambers of type MB1, MB2, and MB3, is 0.03 ± 0.01.
The DT Local Trigger in station type MB4 provides a lower fraction of double triggers, namely
0.012 ± 0.005, since only correlated trigger segments are provided by this station type. The
uncertainty reflects the observed spread of values among the various chambers, due to systematic effects like noisy channels, or different angles of incidence of the cosmic rays. The results
are consistent with test beam measurements [9, 10]. The false dimuon Level-1 trigger rate in
11
3.4 Position and Angular Resolution
0.22
R.M.S. = 0.8 mm
CMS 2008
0.2
0.18
0.16
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Fraction of Triggers
Fraction of Triggers
the barrel region is further suppressed, as the matching of at least two segments in two different chambers is required to form a trigger candidate, and as a further selection is applied by
the Global Muon Trigger. The measured false dimuon trigger rate per chamber is significantly
smaller compared to the assumptions made in Ref. [4]. Hence, the false dimuon Level-1 rate in
the barrel region is estimated to be below the 0.1 % reported in Ref. [4], which is at least one
order of magnitude smaller than the real dimuon rate and can, therefore, be neglected.
0.06
R.M.S. = 4 mrad
CMS 2008
0.05
0.04
0.12
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0.1
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0.02
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0
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-20
-10
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10
20
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Incidence angle difference [mrad]
Figure 9: Left: distribution of the difference between the position of the local track segment and
the trigger segment. Right: distribution of the difference between the incidence angle measured
by the local track segment and the trigger segment. Results are shown for a chamber of type
MB1.
3.4
Position and Angular Resolution
The track segments obtained by fitting the TDC information in each chamber and used for
offline muon reconstruction provide an accurate determination of the position and the incidence angle of the muon in the chamber independent of the trigger output. These quantities
are compared with the corresponding information assigned by the DT Local Trigger to the trigger segments, Φ and Φb . Figure 9 (left) shows the distribution of the difference between the
position computed by the reconstructed track segment and by the trigger segment for a chamber of type MB1 taken as an example. The RMS of the distribution is 0.8 mm. This provides an
estimate of the position resolution of the trigger segment, which is the same for every station
type. This measurement is in agreement with previous test beam results [9]. The uncertainty
related to the track position measurement is neglected.
A similar study is performed on the track incidence angle ψ. Figure 9 (right) shows the distribution of the difference between the incidence angle of the reconstructed track and the trigger
segment. The RMS of the distribution is 4 mrad. Taking into account the slight reduction of the
angular resolution arising from the timing characteristics of the cosmic rays, the resolution is in
agreement with the value of 3 mrad obtained in previous test beam measurements [9]. The result guarantees that the expected performance in terms of position and transverse momentum
resolution at the output of the Level-1 trigger will be achieved for collision data taking [4].
12
3.5
3
Performance of the DT Local Trigger
Effect of the Magnetic Field
In station type MB1 of the wheels +2 and −2, the magnetic field is expected to affect the driftpath lengths such that the maximum drift time is increased by O (10 ns) [17]. A variation of
the maximum drift time, which corresponds to an apparent change of the drift velocity, could
degrade the DT Local Trigger performance, affecting in particular the BX identification. A
sample of approximately 5 million events collected with no magnetic field is used to study this
effect. The means of the BX distributions determined by the DT Local Trigger in a chamber
(obtained as in Fig. 7) are compared for data taken with and without the magnetic field.
Some corrections are applied to compare the results obtained from the two data sets. As muons
are bent by the magnetic field, the timing of the trigger signals between the various chambers
and sectors is slightly affected because of the different path length, especially for low momentum particles. In addition, some further adjustments in the synchronization between the various sectors were performed between the two data taking periods. Therefore, a direct comparison of the means of the BX distributions obtained in the two conditions is biased by these
systematic effects. As in station type MB4 the effect of the magnetic field on the drift velocity
is expected to be negligible, it is assumed that in this case any deviation from zero observed in
the difference of the BX distributions is entirely due to the systematic effects. Results for station
type MB4 are then set to zero, separately in each sector, and the results for the other stations
are shifted by the same amount to correct for the systematic effects.
Figure 10 shows the difference between the means of the BX distributions, with and without
the magnetic field, as a function of the wheel number for different station types, after the correction procedure described above. The results are averaged over the various sectors, and only
statistical uncertainties are shown in the figure. Small deviations from zero are observed in all
stations and wheels, and they are partially due to the aforementioned systematic uncertainties, which could not be completely suppressed. The largest deviation from zero is observed
in MB1, at the wheels +2 and −2, where the magnetic field is indeed expected to have the
largest effect on BX identification. Comparing results with and without the magnetic field, the
maximum average BX displacement is 0.1 units of a BX, corresponding to about 3 ns. This shift
is much smaller than 25 ns, which is the time between two consecutive BXs, and thus it cannot
significantly affect the performance of the trigger [17].
A study of the BX displacement as a function of the position of the trigger candidate along
the z coordinate shows that the BX assignment is fairly constant across the muon chambers,
increasing at the edges with the maximum value of 5 ns, which is sufficiently small compared
to 25 ns. Consequently it is possible to configure the BTIs with the same value of the driftvelocity parameter in each chamber, regardless of its location in the detector or the magnetic
field.
The comparison between events recorded with and without the magnetic field is used to study
the effect of the field on the position and angular resolution of the trigger segments. The results
show that the position and direction determination by the DT Local Trigger is not affected
by the presence of the magnetic field. The comparison of data taken with and without the
magnetic field also shows that the magnetic field does not affect the trigger efficiency, except in
station MB1 of the wheels +2 and −2 where the fraction of correlated triggers is decreased by
less than 2 %.
BX mean (B = 3.8 T) - BX mean (B = 0)
13
0.4
CMS 2008
0.3
0.2
0.1
0
MB1
-0.1
MB2
MB3
-0.2
-0.3
-2
-1
0
1
2
Wheel
Figure 10: Difference between the means of the BX distributions determined by the DT Local
Trigger with and without magnetic field, in units of BX, as a function of the wheel number, for
MB1, MB2 and MB3 station types.
4 Comparison with the Emulator
A detailed simulation of the DT Local Trigger selection algorithm is implemented in the CMS
software framework, and is part of the emulator program that reproduces the output of the
entire Level-1 trigger. The emulator processes the signals from the drift cells: for each cell the
difference tDigi − tTrig is computed and sent as input to the emulator. The quantity received
as input by the trigger electronics is not exactly the same as tDigi − tTrig , although its physical
meaning is the same. In fact, the BTIs are directly linked to the wires of the DT chamber, receiving discriminated signals on the on-board electronics, while the quantity tDigi and the pedestal
parameter tTrig are determined by the TDCs (which have a different hardware connection to the
DT cells with respect to the BTIs) and by an offline analysis, respectively. This makes the exact
data-emulator agreement impossible by design. Discrepancies between data and emulation,
on an event-by-event comparison, are mostly observed in the quality of the trigger primitives.
Even considering this intrinsic limitation, an event-by-event comparison shows that, among all
the trigger primitives provided by the trigger electronics, more than 90 % are perfectly reproduced by the emulator in all their characteristics. If the comparison between data and emulator
is performed on a statistical basis rather than event-by-event, the differences between data and
emulator largely compensate, and the agreement approaches 100 %. This can be seen in Fig. 11,
which shows the comparison of the distribution of the trigger quality for station types MB1
and MB4.
The emulator program assumes a perfectly working trigger system, so that any significant discrepancy with the data is an indication either of malfunctioning electronics or mis-configuration.
On the other hand, dead cells, high-voltage problems, noisy cells, or any other malfunctions
affecting the presence of the digitized information from the TDCs, but not related to the trigger
devices, are always reproduced by the emulation, resulting in a very good matching with the
data. Therefore, the emulator is a very powerful tool for use during data taking for diagnosing
problems that are related to the trigger system.
14
0.7
CMS 2008
MB 1
0.6
0.5
0.4
Trigger Data
Emulator
0.3
Fraction of triggers
Fraction of triggers
5
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.1
HI
HO
LL
HL
HH
Trigger quality
CMS 2008
MB 4
0.2
0
Conclusions
0
Trigger Data
Emulator
HI
HO
LL
HL
HH
Trigger quality
Figure 11: Distribution of the quality of the trigger segments, for data and emulation, for station
types MB1 (left) and MB4 (right).
5 Conclusions
The muon Local Trigger based on the drift-tube detector of the CMS experiment has been extensively tested during the commissioning of the apparatus using cosmic rays. Cosmic rays
traverse the detector at arbitrary times and with different directions compared to particles produced in LHC collisions, for which the muon trigger was designed. Therefore, the system
performance is degraded with respect to the expectations for the LHC, or if compared with
measurements previously performed with bunched beams. Nevertheless, the device operated
in a very efficient and reliable way. An overall efficiency of 95 % is obtained, and 48 % of the
trigger segments are of the best possible quality. An accurate measurement of the trigger efficiency as a function of the timing of the system shows that, in the time window where the
trigger electronics is properly synchronized with the arriving muon, as it will be the case for
particles produced at LHC collisions, the DT Local trigger efficiency is 97 % for any trigger
quality. The performance of the BX identification reaches 100 % when a correction for the arbitrary arrival time of cosmic ray muons is performed. The rate of false double triggers for single
muons is about 1.5–3.0 % of the single muon triggers in one chamber. As the coincidence of trigger segments in at least two chambers is needed by the Phi Track Finder to reconstruct a trigger
candidate, and as a further selection is applied by the Regional and the Global Muon Trigger,
the false dimuon trigger rate is expected to be at least one order of magnitude smaller than
the real dimuon rate expected from LHC collisions at any transverse momentum threshold.
The position and angular resolution of the trigger segments is 0.8 mm and 4 mrad, respectively.
This performance allows the trigger system to achieve the position and transverse momentum
resolution needed for efficient operation with collisions. The magnetic field has a negligible
impact on the bunch crossing identification, on the position and angular resolution, and on the
trigger efficiency, even in the detector regions where the effect should be largest. Trigger data
were also successfully cross-checked with the emulator. Although a perfect event-by-event
agreement with the data is impossible by design, more than 90 % of the trigger primitives are
perfectly reproduced by the emulator in all their characteristics. This makes the emulator a
powerful tool for diagnosing problems related to the trigger system during data taking.
15
Acknowledgements
We thank the technical and administrative staff at CERN and other CMS Institutes, and acknowledge support from: FMSR (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ
and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST and NSFC (China); COLCIENCIAS
(Colombia); MSES (Croatia); RPF (Cyprus); Academy of Sciences and NICPB (Estonia); ME,
HIP and Academy of Finland (Finland); CEA and CNRS/IN2P3 (France); BMBF and DESY
(Germany); BMBF, DFG and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary);
DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF (Korea); LAS (Lithuania);
CINVESTAV, CONACYT, SEP and UASLP-FAI (Mexico); PAEC (Pakistan); SCSR (Poland); FCT
(Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MST and MAE (Russia);
MSTDS (Serbia); MCINN and CPAN (Spain); Swiss Funding Agencies (Switzerland); NSC
(Taipei); TUBITAK and TAEK (Turkey); STFC (United Kingdom); DOE and NSF (USA). Individuals have received support from the Marie-Curie IEF program (European Union); the
Leventis Foundation; the A. P. Sloan Foundation; and the Alexander von Humboldt Foundation
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17
A
The CMS Collaboration
Yerevan Physics Institute, Yerevan, Armenia
S. Chatrchyan, V. Khachatryan, A.M. Sirunyan
Institut für Hochenergiephysik der OeAW, Wien, Austria
W. Adam, B. Arnold, H. Bergauer, T. Bergauer, M. Dragicevic, M. Eichberger, J. Erö, M. Friedl,
R. Frühwirth, V.M. Ghete, J. Hammer1 , S. Hänsel, M. Hoch, N. Hörmann, J. Hrubec, M. Jeitler,
G. Kasieczka, K. Kastner, M. Krammer, D. Liko, I. Magrans de Abril, I. Mikulec, F. Mittermayr,
B. Neuherz, M. Oberegger, M. Padrta, M. Pernicka, H. Rohringer, S. Schmid, R. Schöfbeck,
T. Schreiner, R. Stark, H. Steininger, J. Strauss, A. Taurok, F. Teischinger, T. Themel, D. Uhl,
P. Wagner, W. Waltenberger, G. Walzel, E. Widl, C.-E. Wulz
National Centre for Particle and High Energy Physics, Minsk, Belarus
V. Chekhovsky, O. Dvornikov, I. Emeliantchik, A. Litomin, V. Makarenko, I. Marfin,
V. Mossolov, N. Shumeiko, A. Solin, R. Stefanovitch, J. Suarez Gonzalez, A. Tikhonov
Research Institute for Nuclear Problems, Minsk, Belarus
A. Fedorov, A. Karneyeu, M. Korzhik, V. Panov, R. Zuyeuski
Research Institute of Applied Physical Problems, Minsk, Belarus
P. Kuchinsky
Universiteit Antwerpen, Antwerpen, Belgium
W. Beaumont, L. Benucci, M. Cardaci, E.A. De Wolf, E. Delmeire, D. Druzhkin, M. Hashemi,
X. Janssen, T. Maes, L. Mucibello, S. Ochesanu, R. Rougny, M. Selvaggi, H. Van Haevermaet,
P. Van Mechelen, N. Van Remortel
Vrije Universiteit Brussel, Brussel, Belgium
V. Adler, S. Beauceron, S. Blyweert, J. D’Hondt, S. De Weirdt, O. Devroede, J. Heyninck, A. Kalogeropoulos, J. Maes, M. Maes, M.U. Mozer, S. Tavernier, W. Van Doninck1 , P. Van Mulders,
I. Villella
Université Libre de Bruxelles, Bruxelles, Belgium
O. Bouhali, E.C. Chabert, O. Charaf, B. Clerbaux, G. De Lentdecker, V. Dero, S. Elgammal,
A.P.R. Gay, G.H. Hammad, P.E. Marage, S. Rugovac, C. Vander Velde, P. Vanlaer, J. Wickens
Ghent University, Ghent, Belgium
M. Grunewald, B. Klein, A. Marinov, D. Ryckbosch, F. Thyssen, M. Tytgat, L. Vanelderen,
P. Verwilligen
Université Catholique de Louvain, Louvain-la-Neuve, Belgium
S. Basegmez, G. Bruno, J. Caudron, C. Delaere, P. Demin, D. Favart, A. Giammanco,
G. Grégoire, V. Lemaitre, O. Militaru, S. Ovyn, K. Piotrzkowski1 , L. Quertenmont, N. Schul
Université de Mons, Mons, Belgium
N. Beliy, E. Daubie
Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, Brazil
G.A. Alves, M.E. Pol, M.H.G. Souza
Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil
W. Carvalho, D. De Jesus Damiao, C. De Oliveira Martins, S. Fonseca De Souza, L. Mundim,
V. Oguri, A. Santoro, S.M. Silva Do Amaral, A. Sznajder
Instituto de Fisica Teorica, Universidade Estadual Paulista, Sao Paulo, Brazil
18
A The CMS Collaboration
T.R. Fernandez Perez Tomei, M.A. Ferreira Dias, E. M. Gregores2 , S.F. Novaes
Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria
K. Abadjiev1 , T. Anguelov, J. Damgov, N. Darmenov1 , L. Dimitrov, V. Genchev1 , P. Iaydjiev,
S. Piperov, S. Stoykova, G. Sultanov, R. Trayanov, I. Vankov
University of Sofia, Sofia, Bulgaria
A. Dimitrov, M. Dyulendarova, V. Kozhuharov, L. Litov, E. Marinova, M. Mateev, B. Pavlov,
P. Petkov, Z. Toteva1
Institute of High Energy Physics, Beijing, China
G.M. Chen, H.S. Chen, W. Guan, C.H. Jiang, D. Liang, B. Liu, X. Meng, J. Tao, J. Wang, Z. Wang,
Z. Xue, Z. Zhang
State Key Lab. of Nucl. Phys. and Tech., Peking University, Beijing, China
Y. Ban, J. Cai, Y. Ge, S. Guo, Z. Hu, Y. Mao, S.J. Qian, H. Teng, B. Zhu
Universidad de Los Andes, Bogota, Colombia
C. Avila, M. Baquero Ruiz, C.A. Carrillo Montoya, A. Gomez, B. Gomez Moreno, A.A. Ocampo
Rios, A.F. Osorio Oliveros, D. Reyes Romero, J.C. Sanabria
Technical University of Split, Split, Croatia
N. Godinovic, K. Lelas, R. Plestina, D. Polic, I. Puljak
University of Split, Split, Croatia
Z. Antunovic, M. Dzelalija
Institute Rudjer Boskovic, Zagreb, Croatia
V. Brigljevic, S. Duric, K. Kadija, S. Morovic
University of Cyprus, Nicosia, Cyprus
R. Fereos, M. Galanti, J. Mousa, A. Papadakis, F. Ptochos, P.A. Razis, D. Tsiakkouri, Z. Zinonos
National Institute of Chemical Physics and Biophysics, Tallinn, Estonia
A. Hektor, M. Kadastik, K. Kannike, M. Müntel, M. Raidal, L. Rebane
Helsinki Institute of Physics, Helsinki, Finland
E. Anttila, S. Czellar, J. Härkönen, A. Heikkinen, V. Karimäki, R. Kinnunen, J. Klem, M.J. Kortelainen, T. Lampén, K. Lassila-Perini, S. Lehti, T. Lindén, P. Luukka, T. Mäenpää, J. Nysten,
E. Tuominen, J. Tuominiemi, D. Ungaro, L. Wendland
Lappeenranta University of Technology, Lappeenranta, Finland
K. Banzuzi, A. Korpela, T. Tuuva
Laboratoire d’Annecy-le-Vieux de Physique des Particules, IN2P3-CNRS, Annecy-le-Vieux,
France
P. Nedelec, D. Sillou
DSM/IRFU, CEA/Saclay, Gif-sur-Yvette, France
M. Besancon, R. Chipaux, M. Dejardin, D. Denegri, J. Descamps, B. Fabbro, J.L. Faure, F. Ferri,
S. Ganjour, F.X. Gentit, A. Givernaud, P. Gras, G. Hamel de Monchenault, P. Jarry, M.C. Lemaire,
E. Locci, J. Malcles, M. Marionneau, L. Millischer, J. Rander, A. Rosowsky, D. Rousseau,
M. Titov, P. Verrecchia
Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France
S. Baffioni, L. Bianchini, M. Bluj3 , P. Busson, C. Charlot, L. Dobrzynski, R. Granier de Cassagnac, M. Haguenauer, P. Miné, P. Paganini, Y. Sirois, C. Thiebaux, A. Zabi
19
Institut Pluridisciplinaire Hubert Curien, Université de Strasbourg, Université de Haute
Alsace Mulhouse, CNRS/IN2P3, Strasbourg, France
J.-L. Agram4 , A. Besson, D. Bloch, D. Bodin, J.-M. Brom, E. Conte4 , F. Drouhin4 , J.-C. Fontaine4 ,
D. Gelé, U. Goerlach, L. Gross, P. Juillot, A.-C. Le Bihan, Y. Patois, J. Speck, P. Van Hove
Université de Lyon, Université Claude Bernard Lyon 1, CNRS-IN2P3, Institut de Physique
Nucléaire de Lyon, Villeurbanne, France
C. Baty, M. Bedjidian, J. Blaha, G. Boudoul, H. Brun, N. Chanon, R. Chierici, D. Contardo,
P. Depasse, T. Dupasquier, H. El Mamouni, F. Fassi5 , J. Fay, S. Gascon, B. Ille, T. Kurca, T. Le
Grand, M. Lethuillier, N. Lumb, L. Mirabito, S. Perries, M. Vander Donckt, P. Verdier
E. Andronikashvili Institute of Physics, Academy of Science, Tbilisi, Georgia
N. Djaoshvili, N. Roinishvili, V. Roinishvili
Institute of High Energy Physics and Informatization, Tbilisi State University, Tbilisi,
Georgia
N. Amaglobeli
RWTH Aachen University, I. Physikalisches Institut, Aachen, Germany
R. Adolphi, G. Anagnostou, R. Brauer, W. Braunschweig, M. Edelhoff, H. Esser, L. Feld,
W. Karpinski, A. Khomich, K. Klein, N. Mohr, A. Ostaptchouk, D. Pandoulas, G. Pierschel,
F. Raupach, S. Schael, A. Schultz von Dratzig, G. Schwering, D. Sprenger, M. Thomas, M. Weber,
B. Wittmer, M. Wlochal
RWTH Aachen University, III. Physikalisches Institut A, Aachen, Germany
O. Actis, G. Altenhöfer, W. Bender, P. Biallass, M. Erdmann, G. Fetchenhauer1 , J. Frangenheim,
T. Hebbeker, G. Hilgers, A. Hinzmann, K. Hoepfner, C. Hof, M. Kirsch, T. Klimkovich,
P. Kreuzer1 , D. Lanske† , M. Merschmeyer, A. Meyer, B. Philipps, H. Pieta, H. Reithler,
S.A. Schmitz, L. Sonnenschein, M. Sowa, J. Steggemann, H. Szczesny, D. Teyssier, C. Zeidler
RWTH Aachen University, III. Physikalisches Institut B, Aachen, Germany
M. Bontenackels, M. Davids, M. Duda, G. Flügge, H. Geenen, M. Giffels, W. Haj Ahmad, T. Hermanns, D. Heydhausen, S. Kalinin, T. Kress, A. Linn, A. Nowack, L. Perchalla, M. Poettgens,
O. Pooth, P. Sauerland, A. Stahl, D. Tornier, M.H. Zoeller
Deutsches Elektronen-Synchrotron, Hamburg, Germany
M. Aldaya Martin, U. Behrens, K. Borras, A. Campbell, E. Castro, D. Dammann, G. Eckerlin,
A. Flossdorf, G. Flucke, A. Geiser, D. Hatton, J. Hauk, H. Jung, M. Kasemann, I. Katkov,
C. Kleinwort, H. Kluge, A. Knutsson, E. Kuznetsova, W. Lange, W. Lohmann, R. Mankel1 ,
M. Marienfeld, A.B. Meyer, S. Miglioranzi, J. Mnich, M. Ohlerich, J. Olzem, A. Parenti,
C. Rosemann, R. Schmidt, T. Schoerner-Sadenius, D. Volyanskyy, C. Wissing, W.D. Zeuner1
University of Hamburg, Hamburg, Germany
C. Autermann, F. Bechtel, J. Draeger, D. Eckstein, U. Gebbert, K. Kaschube, G. Kaussen,
R. Klanner, B. Mura, S. Naumann-Emme, F. Nowak, U. Pein, C. Sander, P. Schleper, T. Schum,
H. Stadie, G. Steinbrück, J. Thomsen, R. Wolf
Institut für Experimentelle Kernphysik, Karlsruhe, Germany
J. Bauer, P. Blüm, V. Buege, A. Cakir, T. Chwalek, W. De Boer, A. Dierlamm, G. Dirkes,
M. Feindt, U. Felzmann, M. Frey, A. Furgeri, J. Gruschke, C. Hackstein, F. Hartmann1 ,
S. Heier, M. Heinrich, H. Held, D. Hirschbuehl, K.H. Hoffmann, S. Honc, C. Jung, T. Kuhr,
T. Liamsuwan, D. Martschei, S. Mueller, Th. Müller, M.B. Neuland, M. Niegel, O. Oberst,
A. Oehler, J. Ott, T. Peiffer, D. Piparo, G. Quast, K. Rabbertz, F. Ratnikov, N. Ratnikova, M. Renz,
C. Saout1 , G. Sartisohn, A. Scheurer, P. Schieferdecker, F.-P. Schilling, G. Schott, H.J. Simonis,
20
A The CMS Collaboration
F.M. Stober, P. Sturm, D. Troendle, A. Trunov, W. Wagner, J. Wagner-Kuhr, M. Zeise, V. Zhukov6 ,
E.B. Ziebarth
Institute of Nuclear Physics ”Demokritos”, Aghia Paraskevi, Greece
G. Daskalakis, T. Geralis, K. Karafasoulis, A. Kyriakis, D. Loukas, A. Markou, C. Markou,
C. Mavrommatis, E. Petrakou, A. Zachariadou
University of Athens, Athens, Greece
L. Gouskos, P. Katsas, A. Panagiotou1
University of Ioánnina, Ioánnina, Greece
I. Evangelou, P. Kokkas, N. Manthos, I. Papadopoulos, V. Patras, F.A. Triantis
KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary
G. Bencze1 , L. Boldizsar, G. Debreczeni, C. Hajdu1 , S. Hernath, P. Hidas, D. Horvath7 , K. Krajczar, A. Laszlo, G. Patay, F. Sikler, N. Toth, G. Vesztergombi
Institute of Nuclear Research ATOMKI, Debrecen, Hungary
N. Beni, G. Christian, J. Imrek, J. Molnar, D. Novak, J. Palinkas, G. Szekely, Z. Szillasi1 ,
K. Tokesi, V. Veszpremi
University of Debrecen, Debrecen, Hungary
A. Kapusi, G. Marian, P. Raics, Z. Szabo, Z.L. Trocsanyi, B. Ujvari, G. Zilizi
Panjab University, Chandigarh, India
S. Bansal, H.S. Bawa, S.B. Beri, V. Bhatnagar, M. Jindal, M. Kaur, R. Kaur, J.M. Kohli,
M.Z. Mehta, N. Nishu, L.K. Saini, A. Sharma, A. Singh, J.B. Singh, S.P. Singh
University of Delhi, Delhi, India
S. Ahuja, S. Arora, S. Bhattacharya8 , S. Chauhan, B.C. Choudhary, P. Gupta, S. Jain, S. Jain,
M. Jha, A. Kumar, K. Ranjan, R.K. Shivpuri, A.K. Srivastava
Bhabha Atomic Research Centre, Mumbai, India
R.K. Choudhury, D. Dutta, S. Kailas, S.K. Kataria, A.K. Mohanty, L.M. Pant, P. Shukla, A. Topkar
Tata Institute of Fundamental Research - EHEP, Mumbai, India
T. Aziz, M. Guchait9 , A. Gurtu, M. Maity10 , D. Majumder, G. Majumder, K. Mazumdar,
A. Nayak, A. Saha, K. Sudhakar
Tata Institute of Fundamental Research - HECR, Mumbai, India
S. Banerjee, S. Dugad, N.K. Mondal
Institute for Studies in Theoretical Physics & Mathematics (IPM), Tehran, Iran
H. Arfaei, H. Bakhshiansohi, A. Fahim, A. Jafari, M. Mohammadi Najafabadi, A. Moshaii,
S. Paktinat Mehdiabadi, S. Rouhani, B. Safarzadeh, M. Zeinali
University College Dublin, Dublin, Ireland
M. Felcini
INFN Sezione di Bari a , Università di Bari b , Politecnico di Bari c , Bari, Italy
M. Abbresciaa,b , L. Barbonea , F. Chiumaruloa , A. Clementea , A. Colaleoa , D. Creanzaa,c ,
G. Cuscelaa , N. De Filippisa , M. De Palmaa,b , G. De Robertisa , G. Donvitoa , F. Fedelea , L. Fiorea ,
M. Francoa , G. Iasellia,c , N. Lacalamitaa , F. Loddoa , L. Lusitoa,b , G. Maggia,c , M. Maggia ,
N. Mannaa,b , B. Marangellia,b , S. Mya,c , S. Natalia,b , S. Nuzzoa,b , G. Papagnia , S. Piccolomoa ,
G.A. Pierroa , C. Pintoa , A. Pompilia,b , G. Pugliesea,c , R. Rajana , A. Ranieria , F. Romanoa,c ,
21
G. Rosellia,b , G. Selvaggia,b , Y. Shindea , L. Silvestrisa , S. Tupputia,b , G. Zitoa
INFN Sezione di Bologna a , Universita di Bologna b , Bologna, Italy
G. Abbiendia , W. Bacchia,b , A.C. Benvenutia , M. Boldinia , D. Bonacorsia , S. BraibantGiacomellia,b , V.D. Cafaroa , S.S. Caiazzaa , P. Capiluppia,b , A. Castroa,b , F.R. Cavalloa ,
G. Codispotia,b , M. Cuffiania,b , I. D’Antonea , G.M. Dallavallea,1 , F. Fabbria , A. Fanfania,b ,
D. Fasanellaa , P. Giacomellia , V. Giordanoa , M. Giuntaa,1 , C. Grandia , M. Guerzonia ,
S. Marcellinia , G. Masettia,b , A. Montanaria , F.L. Navarriaa,b , F. Odoricia , G. Pellegrinia ,
A. Perrottaa , A.M. Rossia,b , T. Rovellia,b , G. Sirolia,b , G. Torromeoa , R. Travaglinia,b
INFN Sezione di Catania a , Universita di Catania b , Catania, Italy
S. Albergoa,b , S. Costaa,b , R. Potenzaa,b , A. Tricomia,b , C. Tuvea
INFN Sezione di Firenze a , Universita di Firenze b , Firenze, Italy
G. Barbaglia , G. Broccoloa,b , V. Ciullia,b , C. Civininia , R. D’Alessandroa,b , E. Focardia,b ,
S. Frosalia,b , E. Galloa , C. Gentaa,b , G. Landia,b , P. Lenzia,b,1 , M. Meschinia , S. Paolettia ,
G. Sguazzonia , A. Tropianoa
INFN Laboratori Nazionali di Frascati, Frascati, Italy
L. Benussi, M. Bertani, S. Bianco, S. Colafranceschi11 , D. Colonna11 , F. Fabbri, M. Giardoni,
L. Passamonti, D. Piccolo, D. Pierluigi, B. Ponzio, A. Russo
INFN Sezione di Genova, Genova, Italy
P. Fabbricatore, R. Musenich
INFN Sezione di Milano-Biccoca a , Universita di Milano-Bicocca b , Milano, Italy
A. Benagliaa , M. Callonia , G.B. Ceratia,b,1 , P. D’Angeloa , F. De Guioa , F.M. Farinaa , A. Ghezzia ,
P. Govonia,b , M. Malbertia,b,1 , S. Malvezzia , A. Martellia , D. Menascea , V. Miccioa,b , L. Moronia ,
P. Negria,b , M. Paganonia,b , D. Pedrinia , A. Pulliaa,b , S. Ragazzia,b , N. Redaellia , S. Salaa ,
R. Salernoa,b , T. Tabarelli de Fatisa,b , V. Tancinia,b , S. Taronia,b
INFN Sezione di Napoli a , Universita di Napoli ”Federico II” b , Napoli, Italy
S. Buontempoa , N. Cavalloa , A. Cimminoa,b,1 , M. De Gruttolaa,b,1 , F. Fabozzia,12 , A.O.M. Iorioa ,
L. Listaa , D. Lomidzea , P. Nolia,b , P. Paoluccia , C. Sciaccaa,b
INFN Sezione di Padova a , Università di Padova b , Padova, Italy
P. Azzia,1 , N. Bacchettaa , L. Barcellana , P. Bellana,b,1 , M. Bellatoa , M. Benettonia , M. Biasottoa,13 ,
D. Biselloa,b , E. Borsatoa,b , A. Brancaa , R. Carlina,b , L. Castellania , P. Checchiaa , E. Contia ,
F. Dal Corsoa , M. De Mattiaa,b , T. Dorigoa , U. Dossellia , F. Fanzagoa , F. Gasparinia,b ,
U. Gasparinia,b , P. Giubilatoa,b , F. Gonellaa , A. Greselea,14 , M. Gulminia,13 , A. Kaminskiya,b ,
S. Lacapraraa,13 , I. Lazzizzeraa,14 , M. Margonia,b , G. Marona,13 , S. Mattiazzoa,b , M. Mazzucatoa ,
M. Meneghellia , A.T. Meneguzzoa,b , M. Michelottoa , F. Montecassianoa , M. Nespoloa ,
M. Passaseoa , M. Pegoraroa , L. Perrozzia , N. Pozzobona,b , P. Ronchesea,b , F. Simonettoa,b ,
N. Tonioloa , E. Torassaa , M. Tosia,b , A. Triossia , S. Vaninia,b , S. Venturaa , P. Zottoa,b ,
G. Zumerlea,b
INFN Sezione di Pavia a , Universita di Pavia b , Pavia, Italy
P. Baessoa,b , U. Berzanoa , S. Bricolaa , M.M. Necchia,b , D. Paganoa,b , S.P. Rattia,b , C. Riccardia,b ,
P. Torrea,b , A. Vicinia , P. Vituloa,b , C. Viviania,b
INFN Sezione di Perugia a , Universita di Perugia b , Perugia, Italy
D. Aisaa , S. Aisaa , E. Babuccia , M. Biasinia,b , G.M. Bileia , B. Caponeria,b , B. Checcuccia , N. Dinua ,
L. Fanòa , L. Farnesinia , P. Laricciaa,b , A. Lucaronia,b , G. Mantovania,b , A. Nappia,b , A. Pilusoa ,
V. Postolachea , A. Santocchiaa,b , L. Servolia , D. Tonoiua , A. Vedaeea , R. Volpea,b
22
A The CMS Collaboration
INFN Sezione di Pisa a , Universita di Pisa b , Scuola Normale Superiore di Pisa c , Pisa, Italy
P. Azzurria,c , G. Bagliesia , J. Bernardinia,b , L. Berrettaa , T. Boccalia , A. Boccia,c , L. Borrelloa,c ,
F. Bosia , F. Calzolaria , R. Castaldia , R. Dell’Orsoa , F. Fioria,b , L. Foàa,c , S. Gennaia,c , A. Giassia ,
A. Kraana , F. Ligabuea,c , T. Lomtadzea , F. Mariania , L. Martinia , M. Massaa , A. Messineoa,b ,
A. Moggia , F. Pallaa , F. Palmonaria , G. Petragnania , G. Petrucciania,c , F. Raffaellia , S. Sarkara ,
G. Segneria , A.T. Serbana , P. Spagnoloa,1 , R. Tenchinia,1 , S. Tolainia , G. Tonellia,b,1 , A. Venturia ,
P.G. Verdinia
INFN Sezione di Roma a , Universita di Roma ”La Sapienza” b , Roma, Italy
S. Baccaroa,15 , L. Baronea,b , A. Bartolonia , F. Cavallaria,1 , I. Dafineia , D. Del Rea,b , E. Di
Marcoa,b , M. Diemoza , D. Francia,b , E. Longoa,b , G. Organtinia,b , A. Palmaa,b , F. Pandolfia,b ,
R. Paramattia,1 , F. Pellegrinoa , S. Rahatloua,b , C. Rovellia
INFN Sezione di Torino a , Università di Torino b , Università del Piemonte Orientale (Novara) c , Torino, Italy
G. Alampia , N. Amapanea,b , R. Arcidiaconoa,b , S. Argiroa,b , M. Arneodoa,c , C. Biinoa ,
M.A. Borgiaa,b , C. Bottaa,b , N. Cartigliaa , R. Castelloa,b , G. Cerminaraa,b , M. Costaa,b ,
D. Dattolaa , G. Dellacasaa , N. Demariaa , G. Dugheraa , F. Dumitrachea , A. Grazianoa,b ,
C. Mariottia , M. Maronea,b , S. Masellia , E. Migliorea,b , G. Milaa,b , V. Monacoa,b , M. Musicha,b ,
M. Nervoa,b , M.M. Obertinoa,c , S. Oggeroa,b , R. Paneroa , N. Pastronea , M. Pelliccionia,b ,
A. Romeroa,b , M. Ruspaa,c , R. Sacchia,b , A. Solanoa,b , A. Staianoa , P.P. Trapania,b,1 , D. Trocinoa,b ,
A. Vilela Pereiraa,b , L. Viscaa,b , A. Zampieria
INFN Sezione di Trieste a , Universita di Trieste b , Trieste, Italy
F. Ambroglinia,b , S. Belfortea , F. Cossuttia , G. Della Riccaa,b , B. Gobboa , A. Penzoa
Kyungpook National University, Daegu, Korea
S. Chang, J. Chung, D.H. Kim, G.N. Kim, D.J. Kong, H. Park, D.C. Son
Wonkwang University, Iksan, Korea
S.Y. Bahk
Chonnam National University, Kwangju, Korea
S. Song
Konkuk University, Seoul, Korea
S.Y. Jung
Korea University, Seoul, Korea
B. Hong, H. Kim, J.H. Kim, K.S. Lee, D.H. Moon, S.K. Park, H.B. Rhee, K.S. Sim
Seoul National University, Seoul, Korea
J. Kim
University of Seoul, Seoul, Korea
M. Choi, G. Hahn, I.C. Park
Sungkyunkwan University, Suwon, Korea
S. Choi, Y. Choi, J. Goh, H. Jeong, T.J. Kim, J. Lee, S. Lee
Vilnius University, Vilnius, Lithuania
M. Janulis, D. Martisiute, P. Petrov, T. Sabonis
Centro de Investigacion y de Estudios Avanzados del IPN, Mexico City, Mexico
H. Castilla Valdez1 , A. Sánchez Hernández
23
Universidad Iberoamericana, Mexico City, Mexico
S. Carrillo Moreno
Universidad Autónoma de San Luis Potosı́, San Luis Potosı́, Mexico
A. Morelos Pineda
University of Auckland, Auckland, New Zealand
P. Allfrey, R.N.C. Gray, D. Krofcheck
University of Canterbury, Christchurch, New Zealand
N. Bernardino Rodrigues, P.H. Butler, T. Signal, J.C. Williams
National Centre for Physics, Quaid-I-Azam University, Islamabad, Pakistan
M. Ahmad, I. Ahmed, W. Ahmed, M.I. Asghar, M.I.M. Awan, H.R. Hoorani, I. Hussain,
W.A. Khan, T. Khurshid, S. Muhammad, S. Qazi, H. Shahzad
Institute of Experimental Physics, Warsaw, Poland
M. Cwiok, R. Dabrowski, W. Dominik, K. Doroba, M. Konecki, J. Krolikowski, K. Pozniak16 ,
R. Romaniuk, W. Zabolotny16 , P. Zych
Soltan Institute for Nuclear Studies, Warsaw, Poland
T. Frueboes, R. Gokieli, L. Goscilo, M. Górski, M. Kazana, K. Nawrocki, M. Szleper, G. Wrochna,
P. Zalewski
Laboratório de Instrumentação e Fı́sica Experimental de Partı́culas, Lisboa, Portugal
N. Almeida, L. Antunes Pedro, P. Bargassa, A. David, P. Faccioli, P.G. Ferreira Parracho,
M. Freitas Ferreira, M. Gallinaro, M. Guerra Jordao, P. Martins, G. Mini, P. Musella, J. Pela,
L. Raposo, P.Q. Ribeiro, S. Sampaio, J. Seixas, J. Silva, P. Silva, D. Soares, M. Sousa, J. Varela,
H.K. Wöhri
Joint Institute for Nuclear Research, Dubna, Russia
I. Altsybeev, I. Belotelov, P. Bunin, Y. Ershov, I. Filozova, M. Finger, M. Finger Jr., A. Golunov,
I. Golutvin, N. Gorbounov, V. Kalagin, A. Kamenev, V. Karjavin, V. Konoplyanikov, V. Korenkov, G. Kozlov, A. Kurenkov, A. Lanev, A. Makankin, V.V. Mitsyn, P. Moisenz, E. Nikonov,
D. Oleynik, V. Palichik, V. Perelygin, A. Petrosyan, R. Semenov, S. Shmatov, V. Smirnov,
D. Smolin, E. Tikhonenko, S. Vasil’ev, A. Vishnevskiy, A. Volodko, A. Zarubin, V. Zhiltsov
Petersburg Nuclear Physics Institute, Gatchina (St Petersburg), Russia
N. Bondar, L. Chtchipounov, A. Denisov, Y. Gavrikov, G. Gavrilov, V. Golovtsov, Y. Ivanov,
V. Kim, V. Kozlov, P. Levchenko, G. Obrant, E. Orishchin, A. Petrunin, Y. Shcheglov, A. Shchetkovskiy, V. Sknar, I. Smirnov, V. Sulimov, V. Tarakanov, L. Uvarov, S. Vavilov, G. Velichko,
S. Volkov, A. Vorobyev
Institute for Nuclear Research, Moscow, Russia
Yu. Andreev, A. Anisimov, P. Antipov, A. Dermenev, S. Gninenko, N. Golubev, M. Kirsanov,
N. Krasnikov, V. Matveev, A. Pashenkov, V.E. Postoev, A. Solovey, A. Solovey, A. Toropin,
S. Troitsky
Institute for Theoretical and Experimental Physics, Moscow, Russia
A. Baud, V. Epshteyn, V. Gavrilov, N. Ilina, V. Kaftanov† , V. Kolosov, M. Kossov1 , A. Krokhotin,
S. Kuleshov, A. Oulianov, G. Safronov, S. Semenov, I. Shreyber, V. Stolin, E. Vlasov, A. Zhokin
Moscow State University, Moscow, Russia
E. Boos, M. Dubinin17 , L. Dudko, A. Ershov, A. Gribushin, V. Klyukhin, O. Kodolova, I. Lokhtin,
S. Petrushanko, L. Sarycheva, V. Savrin, A. Snigirev, I. Vardanyan
24
A The CMS Collaboration
P.N. Lebedev Physical Institute, Moscow, Russia
I. Dremin, M. Kirakosyan, N. Konovalova, S.V. Rusakov, A. Vinogradov
State Research Center of Russian Federation, Institute for High Energy Physics, Protvino,
Russia
S. Akimenko, A. Artamonov, I. Azhgirey, S. Bitioukov, V. Burtovoy, V. Grishin1 , V. Kachanov,
D. Konstantinov, V. Krychkine, A. Levine, I. Lobov, V. Lukanin, Y. Mel’nik, V. Petrov, R. Ryutin,
S. Slabospitsky, A. Sobol, A. Sytine, L. Tourtchanovitch, S. Troshin, N. Tyurin, A. Uzunian,
A. Volkov
Vinca Institute of Nuclear Sciences, Belgrade, Serbia
P. Adzic, M. Djordjevic, D. Jovanovic18 , D. Krpic18 , D. Maletic, J. Puzovic18 , N. Smiljkovic
Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT),
Madrid, Spain
M. Aguilar-Benitez, J. Alberdi, J. Alcaraz Maestre, P. Arce, J.M. Barcala, C. Battilana, C. Burgos
Lazaro, J. Caballero Bejar, E. Calvo, M. Cardenas Montes, M. Cepeda, M. Cerrada, M. Chamizo
Llatas, F. Clemente, N. Colino, M. Daniel, B. De La Cruz, A. Delgado Peris, C. Diez Pardos,
C. Fernandez Bedoya, J.P. Fernández Ramos, A. Ferrando, J. Flix, M.C. Fouz, P. Garcia-Abia,
A.C. Garcia-Bonilla, O. Gonzalez Lopez, S. Goy Lopez, J.M. Hernandez, M.I. Josa, J. Marin,
G. Merino, J. Molina, A. Molinero, J.J. Navarrete, J.C. Oller, J. Puerta Pelayo, L. Romero,
J. Santaolalla, C. Villanueva Munoz, C. Willmott, C. Yuste
Universidad Autónoma de Madrid, Madrid, Spain
C. Albajar, M. Blanco Otano, J.F. de Trocóniz, A. Garcia Raboso, J.O. Lopez Berengueres
Universidad de Oviedo, Oviedo, Spain
J. Cuevas, J. Fernandez Menendez, I. Gonzalez Caballero, L. Lloret Iglesias, H. Naves Sordo,
J.M. Vizan Garcia
Instituto de Fı́sica de Cantabria (IFCA), CSIC-Universidad de Cantabria, Santander, Spain
I.J. Cabrillo, A. Calderon, S.H. Chuang, I. Diaz Merino, C. Diez Gonzalez, J. Duarte Campderros, M. Fernandez, G. Gomez, J. Gonzalez Sanchez, R. Gonzalez Suarez, C. Jorda, P. Lobelle
Pardo, A. Lopez Virto, J. Marco, R. Marco, C. Martinez Rivero, P. Martinez Ruiz del Arbol,
F. Matorras, T. Rodrigo, A. Ruiz Jimeno, L. Scodellaro, M. Sobron Sanudo, I. Vila, R. Vilar
Cortabitarte
CERN, European Organization for Nuclear Research, Geneva, Switzerland
D. Abbaneo, E. Albert, M. Alidra, S. Ashby, E. Auffray, J. Baechler, P. Baillon, A.H. Ball,
S.L. Bally, D. Barney, F. Beaudette19 , R. Bellan, D. Benedetti, G. Benelli, C. Bernet, P. Bloch,
S. Bolognesi, M. Bona, J. Bos, N. Bourgeois, T. Bourrel, H. Breuker, K. Bunkowski, D. Campi,
T. Camporesi, E. Cano, A. Cattai, J.P. Chatelain, M. Chauvey, T. Christiansen, J.A. Coarasa
Perez, A. Conde Garcia, R. Covarelli, B. Curé, A. De Roeck, V. Delachenal, D. Deyrail, S. Di
Vincenzo20 , S. Dos Santos, T. Dupont, L.M. Edera, A. Elliott-Peisert, M. Eppard, M. Favre,
N. Frank, W. Funk, A. Gaddi, M. Gastal, M. Gateau, H. Gerwig, D. Gigi, K. Gill, D. Giordano,
J.P. Girod, F. Glege, R. Gomez-Reino Garrido, R. Goudard, S. Gowdy, R. Guida, L. Guiducci,
J. Gutleber, M. Hansen, C. Hartl, J. Harvey, B. Hegner, H.F. Hoffmann, A. Holzner, A. Honma,
M. Huhtinen, V. Innocente, P. Janot, G. Le Godec, P. Lecoq, C. Leonidopoulos, R. Loos,
C. Lourenço, A. Lyonnet, A. Macpherson, N. Magini, J.D. Maillefaud, G. Maire, T. Mäki,
L. Malgeri, M. Mannelli, L. Masetti, F. Meijers, P. Meridiani, S. Mersi, E. Meschi, A. Meynet
Cordonnier, R. Moser, M. Mulders, J. Mulon, M. Noy, A. Oh, G. Olesen, A. Onnela, T. Orimoto,
L. Orsini, E. Perez, G. Perinic, J.F. Pernot, P. Petagna, P. Petiot, A. Petrilli, A. Pfeiffer, M. Pierini,
M. Pimiä, R. Pintus, B. Pirollet, H. Postema, A. Racz, S. Ravat, S.B. Rew, J. Rodrigues Antunes,
25
G. Rolandi21 , M. Rovere, V. Ryjov, H. Sakulin, D. Samyn, H. Sauce, C. Schäfer, W.D. Schlatter,
M. Schröder, C. Schwick, A. Sciaba, I. Segoni, A. Sharma, N. Siegrist, P. Siegrist, N. Sinanis,
T. Sobrier, P. Sphicas22 , D. Spiga, M. Spiropulu17 , F. Stöckli, P. Traczyk, P. Tropea, J. Troska,
A. Tsirou, L. Veillet, G.I. Veres, M. Voutilainen, P. Wertelaers, M. Zanetti
Paul Scherrer Institut, Villigen, Switzerland
W. Bertl, K. Deiters, W. Erdmann, K. Gabathuler, R. Horisberger, Q. Ingram, H.C. Kaestli,
S. König, D. Kotlinski, U. Langenegger, F. Meier, D. Renker, T. Rohe, J. Sibille23 ,
A. Starodumov24
Institute for Particle Physics, ETH Zurich, Zurich, Switzerland
B. Betev, L. Caminada25 , Z. Chen, S. Cittolin, D.R. Da Silva Di Calafiori, S. Dambach25 ,
G. Dissertori, M. Dittmar, C. Eggel25 , J. Eugster, G. Faber, K. Freudenreich, C. Grab, A. Hervé,
W. Hintz, P. Lecomte, P.D. Luckey, W. Lustermann, C. Marchica25 , P. Milenovic26 , F. Moortgat, A. Nardulli, F. Nessi-Tedaldi, L. Pape, F. Pauss, T. Punz, A. Rizzi, F.J. Ronga, L. Sala,
A.K. Sanchez, M.-C. Sawley, V. Sordini, B. Stieger, L. Tauscher† , A. Thea, K. Theofilatos,
D. Treille, P. Trüb25 , M. Weber, L. Wehrli, J. Weng, S. Zelepoukine27
Universität Zürich, Zurich, Switzerland
C. Amsler, V. Chiochia, S. De Visscher, C. Regenfus, P. Robmann, T. Rommerskirchen,
A. Schmidt, D. Tsirigkas, L. Wilke
National Central University, Chung-Li, Taiwan
Y.H. Chang, E.A. Chen, W.T. Chen, A. Go, C.M. Kuo, S.W. Li, W. Lin
National Taiwan University (NTU), Taipei, Taiwan
P. Bartalini, P. Chang, Y. Chao, K.F. Chen, W.-S. Hou, Y. Hsiung, Y.J. Lei, S.W. Lin, R.-S. Lu,
J. Schümann, J.G. Shiu, Y.M. Tzeng, K. Ueno, Y. Velikzhanin, C.C. Wang, M. Wang
Cukurova University, Adana, Turkey
A. Adiguzel, A. Ayhan, A. Azman Gokce, M.N. Bakirci, S. Cerci, I. Dumanoglu, E. Eskut,
S. Girgis, E. Gurpinar, I. Hos, T. Karaman, T. Karaman, A. Kayis Topaksu, P. Kurt, G. Önengüt,
G. Önengüt Gökbulut, K. Ozdemir, S. Ozturk, A. Polatöz, K. Sogut28 , B. Tali, H. Topakli,
D. Uzun, L.N. Vergili, M. Vergili
Middle East Technical University, Physics Department, Ankara, Turkey
I.V. Akin, T. Aliev, S. Bilmis, M. Deniz, H. Gamsizkan, A.M. Guler, K. Öcalan, M. Serin, R. Sever,
U.E. Surat, M. Zeyrek
Bogaziçi University, Department of Physics, Istanbul, Turkey
M. Deliomeroglu, D. Demir29 , E. Gülmez, A. Halu, B. Isildak, M. Kaya30 , O. Kaya30 , S. Ozkorucuklu31 , N. Sonmez32
National Scientific Center, Kharkov Institute of Physics and Technology, Kharkov, Ukraine
L. Levchuk, S. Lukyanenko, D. Soroka, S. Zub
University of Bristol, Bristol, United Kingdom
F. Bostock, J.J. Brooke, T.L. Cheng, D. Cussans, R. Frazier, J. Goldstein, N. Grant,
M. Hansen, G.P. Heath, H.F. Heath, C. Hill, B. Huckvale, J. Jackson, C.K. Mackay, S. Metson,
D.M. Newbold33 , K. Nirunpong, V.J. Smith, J. Velthuis, R. Walton
Rutherford Appleton Laboratory, Didcot, United Kingdom
K.W. Bell, C. Brew, R.M. Brown, B. Camanzi, D.J.A. Cockerill, J.A. Coughlan, N.I. Geddes,
K. Harder, S. Harper, B.W. Kennedy, P. Murray, C.H. Shepherd-Themistocleous, I.R. Tomalin,
J.H. Williams† , W.J. Womersley, S.D. Worm
26
A The CMS Collaboration
Imperial College, University of London, London, United Kingdom
R. Bainbridge, G. Ball, J. Ballin, R. Beuselinck, O. Buchmuller, D. Colling, N. Cripps, G. Davies,
M. Della Negra, C. Foudas, J. Fulcher, D. Futyan, G. Hall, J. Hays, G. Iles, G. Karapostoli, B.C. MacEvoy, A.-M. Magnan, J. Marrouche, J. Nash, A. Nikitenko24 , A. Papageorgiou,
M. Pesaresi, K. Petridis, M. Pioppi34 , D.M. Raymond, N. Rompotis, A. Rose, M.J. Ryan,
C. Seez, P. Sharp, G. Sidiropoulos1 , M. Stettler, M. Stoye, M. Takahashi, A. Tapper, C. Timlin,
S. Tourneur, M. Vazquez Acosta, T. Virdee1 , S. Wakefield, D. Wardrope, T. Whyntie, M. Wingham
Brunel University, Uxbridge, United Kingdom
J.E. Cole, I. Goitom, P.R. Hobson, A. Khan, P. Kyberd, D. Leslie, C. Munro, I.D. Reid,
C. Siamitros, R. Taylor, L. Teodorescu, I. Yaselli
Boston University, Boston, USA
T. Bose, M. Carleton, E. Hazen, A.H. Heering, A. Heister, J. St. John, P. Lawson, D. Lazic,
D. Osborne, J. Rohlf, L. Sulak, S. Wu
Brown University, Providence, USA
J. Andrea, A. Avetisyan, S. Bhattacharya, J.P. Chou, D. Cutts, S. Esen, G. Kukartsev, G. Landsberg, M. Narain, D. Nguyen, T. Speer, K.V. Tsang
University of California, Davis, Davis, USA
R. Breedon, M. Calderon De La Barca Sanchez, M. Case, D. Cebra, M. Chertok, J. Conway,
P.T. Cox, J. Dolen, R. Erbacher, E. Friis, W. Ko, A. Kopecky, R. Lander, A. Lister, H. Liu,
S. Maruyama, T. Miceli, M. Nikolic, D. Pellett, J. Robles, M. Searle, J. Smith, M. Squires, J. Stilley,
M. Tripathi, R. Vasquez Sierra, C. Veelken
University of California, Los Angeles, Los Angeles, USA
V. Andreev, K. Arisaka, D. Cline, R. Cousins, S. Erhan1 , J. Hauser, M. Ignatenko, C. Jarvis,
J. Mumford, C. Plager, G. Rakness, P. Schlein† , J. Tucker, V. Valuev, R. Wallny, X. Yang
University of California, Riverside, Riverside, USA
J. Babb, M. Bose, A. Chandra, R. Clare, J.A. Ellison, J.W. Gary, G. Hanson, G.Y. Jeng, S.C. Kao,
F. Liu, H. Liu, A. Luthra, H. Nguyen, G. Pasztor35 , A. Satpathy, B.C. Shen† , R. Stringer, J. Sturdy,
V. Sytnik, R. Wilken, S. Wimpenny
University of California, San Diego, La Jolla, USA
J.G. Branson, E. Dusinberre, D. Evans, F. Golf, R. Kelley, M. Lebourgeois, J. Letts, E. Lipeles,
B. Mangano, J. Muelmenstaedt, M. Norman, S. Padhi, A. Petrucci, H. Pi, M. Pieri, R. Ranieri,
M. Sani, V. Sharma, S. Simon, F. Würthwein, A. Yagil
University of California, Santa Barbara, Santa Barbara, USA
C. Campagnari, M. D’Alfonso, T. Danielson, J. Garberson, J. Incandela, C. Justus, P. Kalavase,
S.A. Koay, D. Kovalskyi, V. Krutelyov, J. Lamb, S. Lowette, V. Pavlunin, F. Rebassoo, J. Ribnik,
J. Richman, R. Rossin, D. Stuart, W. To, J.R. Vlimant, M. Witherell
California Institute of Technology, Pasadena, USA
A. Apresyan, A. Bornheim, J. Bunn, M. Chiorboli, M. Gataullin, D. Kcira, V. Litvine, Y. Ma,
H.B. Newman, C. Rogan, V. Timciuc, J. Veverka, R. Wilkinson, Y. Yang, L. Zhang, K. Zhu,
R.Y. Zhu
Carnegie Mellon University, Pittsburgh, USA
B. Akgun, R. Carroll, T. Ferguson, D.W. Jang, S.Y. Jun, M. Paulini, J. Russ, N. Terentyev,
H. Vogel, I. Vorobiev
27
University of Colorado at Boulder, Boulder, USA
J.P. Cumalat, M.E. Dinardo, B.R. Drell, W.T. Ford, B. Heyburn, E. Luiggi Lopez, U. Nauenberg,
K. Stenson, K. Ulmer, S.R. Wagner, S.L. Zang
Cornell University, Ithaca, USA
L. Agostino, J. Alexander, F. Blekman, D. Cassel, A. Chatterjee, S. Das, L.K. Gibbons, B. Heltsley,
W. Hopkins, A. Khukhunaishvili, B. Kreis, V. Kuznetsov, J.R. Patterson, D. Puigh, A. Ryd, X. Shi,
S. Stroiney, W. Sun, W.D. Teo, J. Thom, J. Vaughan, Y. Weng, P. Wittich
Fairfield University, Fairfield, USA
C.P. Beetz, G. Cirino, C. Sanzeni, D. Winn
Fermi National Accelerator Laboratory, Batavia, USA
S. Abdullin, M.A. Afaq1 , M. Albrow, B. Ananthan, G. Apollinari, M. Atac, W. Badgett, L. Bagby,
J.A. Bakken, B. Baldin, S. Banerjee, K. Banicz, L.A.T. Bauerdick, A. Beretvas, J. Berryhill,
P.C. Bhat, K. Biery, M. Binkley, I. Bloch, F. Borcherding, A.M. Brett, K. Burkett, J.N. Butler,
V. Chetluru, H.W.K. Cheung, F. Chlebana, I. Churin, S. Cihangir, M. Crawford, W. Dagenhart,
M. Demarteau, G. Derylo, D. Dykstra, D.P. Eartly, J.E. Elias, V.D. Elvira, D. Evans, L. Feng,
M. Fischler, I. Fisk, S. Foulkes, J. Freeman, P. Gartung, E. Gottschalk, T. Grassi, D. Green,
Y. Guo, O. Gutsche, A. Hahn, J. Hanlon, R.M. Harris, B. Holzman, J. Howell, D. Hufnagel,
E. James, H. Jensen, M. Johnson, C.D. Jones, U. Joshi, E. Juska, J. Kaiser, B. Klima, S. Kossiakov,
K. Kousouris, S. Kwan, C.M. Lei, P. Limon, J.A. Lopez Perez, S. Los, L. Lueking, G. Lukhanin,
S. Lusin1 , J. Lykken, K. Maeshima, J.M. Marraffino, D. Mason, P. McBride, T. Miao, K. Mishra,
S. Moccia, R. Mommsen, S. Mrenna, A.S. Muhammad, C. Newman-Holmes, C. Noeding,
V. O’Dell, O. Prokofyev, R. Rivera, C.H. Rivetta, A. Ronzhin, P. Rossman, S. Ryu, V. Sekhri,
E. Sexton-Kennedy, I. Sfiligoi, S. Sharma, T.M. Shaw, D. Shpakov, E. Skup, R.P. Smith† , A. Soha,
W.J. Spalding, L. Spiegel, I. Suzuki, P. Tan, W. Tanenbaum, S. Tkaczyk1 , R. Trentadue1 , L. Uplegger, E.W. Vaandering, R. Vidal, J. Whitmore, E. Wicklund, W. Wu, J. Yarba, F. Yumiceva,
J.C. Yun
University of Florida, Gainesville, USA
D. Acosta, P. Avery, V. Barashko, D. Bourilkov, M. Chen, G.P. Di Giovanni, D. Dobur,
A. Drozdetskiy, R.D. Field, Y. Fu, I.K. Furic, J. Gartner, D. Holmes, B. Kim, S. Klimenko,
J. Konigsberg, A. Korytov, K. Kotov, A. Kropivnitskaya, T. Kypreos, A. Madorsky, K. Matchev,
G. Mitselmakher, Y. Pakhotin, J. Piedra Gomez, C. Prescott, V. Rapsevicius, R. Remington,
M. Schmitt, B. Scurlock, D. Wang, J. Yelton
Florida International University, Miami, USA
C. Ceron, V. Gaultney, L. Kramer, L.M. Lebolo, S. Linn, P. Markowitz, G. Martinez, J.L. Rodriguez
Florida State University, Tallahassee, USA
T. Adams, A. Askew, H. Baer, M. Bertoldi, J. Chen, W.G.D. Dharmaratna, S.V. Gleyzer, J. Haas,
S. Hagopian, V. Hagopian, M. Jenkins, K.F. Johnson, E. Prettner, H. Prosper, S. Sekmen
Florida Institute of Technology, Melbourne, USA
M.M. Baarmand, S. Guragain, M. Hohlmann, H. Kalakhety, H. Mermerkaya, R. Ralich, I. Vodopiyanov
University of Illinois at Chicago (UIC), Chicago, USA
B. Abelev, M.R. Adams, I.M. Anghel, L. Apanasevich, V.E. Bazterra, R.R. Betts, J. Callner,
M.A. Castro, R. Cavanaugh, C. Dragoiu, E.J. Garcia-Solis, C.E. Gerber, D.J. Hofman, S. Khalatian, C. Mironov, E. Shabalina, A. Smoron, N. Varelas
28
A The CMS Collaboration
The University of Iowa, Iowa City, USA
U. Akgun, E.A. Albayrak, A.S. Ayan, B. Bilki, R. Briggs, K. Cankocak36 , K. Chung, W. Clarida,
P. Debbins, F. Duru, F.D. Ingram, C.K. Lae, E. McCliment, J.-P. Merlo, A. Mestvirishvili,
M.J. Miller, A. Moeller, J. Nachtman, C.R. Newsom, E. Norbeck, J. Olson, Y. Onel, F. Ozok,
J. Parsons, I. Schmidt, S. Sen, J. Wetzel, T. Yetkin, K. Yi
Johns Hopkins University, Baltimore, USA
B.A. Barnett, B. Blumenfeld, A. Bonato, C.Y. Chien, D. Fehling, G. Giurgiu, A.V. Gritsan,
Z.J. Guo, P. Maksimovic, S. Rappoccio, M. Swartz, N.V. Tran, Y. Zhang
The University of Kansas, Lawrence, USA
P. Baringer, A. Bean, O. Grachov, M. Murray, V. Radicci, S. Sanders, J.S. Wood, V. Zhukova
Kansas State University, Manhattan, USA
D. Bandurin, T. Bolton, K. Kaadze, A. Liu, Y. Maravin, D. Onoprienko, I. Svintradze, Z. Wan
Lawrence Livermore National Laboratory, Livermore, USA
J. Gronberg, J. Hollar, D. Lange, D. Wright
University of Maryland, College Park, USA
D. Baden, R. Bard, M. Boutemeur, S.C. Eno, D. Ferencek, N.J. Hadley, R.G. Kellogg, M. Kirn,
S. Kunori, K. Rossato, P. Rumerio, F. Santanastasio, A. Skuja, J. Temple, M.B. Tonjes, S.C. Tonwar, T. Toole, E. Twedt
Massachusetts Institute of Technology, Cambridge, USA
B. Alver, G. Bauer, J. Bendavid, W. Busza, E. Butz, I.A. Cali, M. Chan, D. D’Enterria, P. Everaerts,
G. Gomez Ceballos, K.A. Hahn, P. Harris, S. Jaditz, Y. Kim, M. Klute, Y.-J. Lee, W. Li, C. Loizides,
T. Ma, M. Miller, S. Nahn, C. Paus, C. Roland, G. Roland, M. Rudolph, G. Stephans, K. Sumorok,
K. Sung, S. Vaurynovich, E.A. Wenger, B. Wyslouch, S. Xie, Y. Yilmaz, A.S. Yoon
University of Minnesota, Minneapolis, USA
D. Bailleux, S.I. Cooper, P. Cushman, B. Dahmes, A. De Benedetti, A. Dolgopolov, P.R. Dudero,
R. Egeland, G. Franzoni, J. Haupt, A. Inyakin37 , K. Klapoetke, Y. Kubota, J. Mans, N. Mirman,
D. Petyt, V. Rekovic, R. Rusack, M. Schroeder, A. Singovsky, J. Zhang
University of Mississippi, University, USA
L.M. Cremaldi, R. Godang, R. Kroeger, L. Perera, R. Rahmat, D.A. Sanders, P. Sonnek, D. Summers
University of Nebraska-Lincoln, Lincoln, USA
K. Bloom, B. Bockelman, S. Bose, J. Butt, D.R. Claes, A. Dominguez, M. Eads, J. Keller, T. Kelly,
I. Kravchenko, J. Lazo-Flores, C. Lundstedt, H. Malbouisson, S. Malik, G.R. Snow
State University of New York at Buffalo, Buffalo, USA
U. Baur, I. Iashvili, A. Kharchilava, A. Kumar, K. Smith, M. Strang
Northeastern University, Boston, USA
G. Alverson, E. Barberis, O. Boeriu, G. Eulisse, G. Govi, T. McCauley, Y. Musienko38 , S. Muzaffar, I. Osborne, T. Paul, S. Reucroft, J. Swain, L. Taylor, L. Tuura
Northwestern University, Evanston, USA
A. Anastassov, B. Gobbi, A. Kubik, R.A. Ofierzynski, A. Pozdnyakov, M. Schmitt, S. Stoynev,
M. Velasco, S. Won
University of Notre Dame, Notre Dame, USA
L. Antonelli, D. Berry, M. Hildreth, C. Jessop, D.J. Karmgard, T. Kolberg, K. Lannon, S. Lynch,
29
N. Marinelli, D.M. Morse, R. Ruchti, J. Slaunwhite, J. Warchol, M. Wayne
The Ohio State University, Columbus, USA
B. Bylsma, L.S. Durkin, J. Gilmore39 , J. Gu, P. Killewald, T.Y. Ling, G. Williams
Princeton University, Princeton, USA
N. Adam, E. Berry, P. Elmer, A. Garmash, D. Gerbaudo, V. Halyo, A. Hunt, J. Jones, E. Laird,
D. Marlow, T. Medvedeva, M. Mooney, J. Olsen, P. Piroué, D. Stickland, C. Tully, J.S. Werner,
T. Wildish, Z. Xie, A. Zuranski
University of Puerto Rico, Mayaguez, USA
J.G. Acosta, M. Bonnett Del Alamo, X.T. Huang, A. Lopez, H. Mendez, S. Oliveros, J.E. Ramirez
Vargas, N. Santacruz, A. Zatzerklyany
Purdue University, West Lafayette, USA
E. Alagoz, E. Antillon, V.E. Barnes, G. Bolla, D. Bortoletto, A. Everett, A.F. Garfinkel, Z. Gecse,
L. Gutay, N. Ippolito, M. Jones, O. Koybasi, A.T. Laasanen, N. Leonardo, C. Liu, V. Maroussov,
P. Merkel, D.H. Miller, N. Neumeister, A. Sedov, I. Shipsey, H.D. Yoo, Y. Zheng
Purdue University Calumet, Hammond, USA
P. Jindal, N. Parashar
Rice University, Houston, USA
V. Cuplov, K.M. Ecklund, F.J.M. Geurts, J.H. Liu, D. Maronde, M. Matveev, B.P. Padley,
R. Redjimi, J. Roberts, L. Sabbatini, A. Tumanov
University of Rochester, Rochester, USA
B. Betchart, A. Bodek, H. Budd, Y.S. Chung, P. de Barbaro, R. Demina, H. Flacher, Y. Gotra,
A. Harel, S. Korjenevski, D.C. Miner, D. Orbaker, G. Petrillo, D. Vishnevskiy, M. Zielinski
The Rockefeller University, New York, USA
A. Bhatti, L. Demortier, K. Goulianos, K. Hatakeyama, G. Lungu, C. Mesropian, M. Yan
Rutgers, the State University of New Jersey, Piscataway, USA
O. Atramentov, E. Bartz, Y. Gershtein, E. Halkiadakis, D. Hits, A. Lath, K. Rose, S. Schnetzer,
S. Somalwar, R. Stone, S. Thomas, T.L. Watts
University of Tennessee, Knoxville, USA
G. Cerizza, M. Hollingsworth, S. Spanier, Z.C. Yang, A. York
Texas A&M University, College Station, USA
J. Asaadi, A. Aurisano, R. Eusebi, A. Golyash, A. Gurrola, T. Kamon, C.N. Nguyen, J. Pivarski,
A. Safonov, S. Sengupta, D. Toback, M. Weinberger
Texas Tech University, Lubbock, USA
N. Akchurin, L. Berntzon, K. Gumus, C. Jeong, H. Kim, S.W. Lee, S. Popescu, Y. Roh, A. Sill,
I. Volobouev, E. Washington, R. Wigmans, E. Yazgan
Vanderbilt University, Nashville, USA
D. Engh, C. Florez, W. Johns, S. Pathak, P. Sheldon
University of Virginia, Charlottesville, USA
D. Andelin, M.W. Arenton, M. Balazs, S. Boutle, M. Buehler, S. Conetti, B. Cox, R. Hirosky,
A. Ledovskoy, C. Neu, D. Phillips II, M. Ronquest, R. Yohay
Wayne State University, Detroit, USA
S. Gollapinni, K. Gunthoti, R. Harr, P.E. Karchin, M. Mattson, A. Sakharov
30
A The CMS Collaboration
University of Wisconsin, Madison, USA
M. Anderson, M. Bachtis, J.N. Bellinger, D. Carlsmith, I. Crotty1 , S. Dasu, S. Dutta, J. Efron,
F. Feyzi, K. Flood, L. Gray, K.S. Grogg, M. Grothe, R. Hall-Wilton1 , M. Jaworski, P. Klabbers,
J. Klukas, A. Lanaro, C. Lazaridis, J. Leonard, R. Loveless, M. Magrans de Abril, A. Mohapatra,
G. Ott, G. Polese, D. Reeder, A. Savin, W.H. Smith, A. Sourkov40 , J. Swanson, M. Weinberg,
D. Wenman, M. Wensveen, A. White
†: Deceased
1: Also at CERN, European Organization for Nuclear Research, Geneva, Switzerland
2: Also at Universidade Federal do ABC, Santo Andre, Brazil
3: Also at Soltan Institute for Nuclear Studies, Warsaw, Poland
4: Also at Université de Haute-Alsace, Mulhouse, France
5: Also at Centre de Calcul de l’Institut National de Physique Nucleaire et de Physique des
Particules (IN2P3), Villeurbanne, France
6: Also at Moscow State University, Moscow, Russia
7: Also at Institute of Nuclear Research ATOMKI, Debrecen, Hungary
8: Also at University of California, San Diego, La Jolla, USA
9: Also at Tata Institute of Fundamental Research - HECR, Mumbai, India
10: Also at University of Visva-Bharati, Santiniketan, India
11: Also at Facolta’ Ingegneria Universita’ di Roma ”La Sapienza”, Roma, Italy
12: Also at Università della Basilicata, Potenza, Italy
13: Also at Laboratori Nazionali di Legnaro dell’ INFN, Legnaro, Italy
14: Also at Università di Trento, Trento, Italy
15: Also at ENEA - Casaccia Research Center, S. Maria di Galeria, Italy
16: Also at Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland
17: Also at California Institute of Technology, Pasadena, USA
18: Also at Faculty of Physics of University of Belgrade, Belgrade, Serbia
19: Also at Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France
20: Also at Alstom Contracting, Geneve, Switzerland
21: Also at Scuola Normale e Sezione dell’ INFN, Pisa, Italy
22: Also at University of Athens, Athens, Greece
23: Also at The University of Kansas, Lawrence, USA
24: Also at Institute for Theoretical and Experimental Physics, Moscow, Russia
25: Also at Paul Scherrer Institut, Villigen, Switzerland
26: Also at Vinca Institute of Nuclear Sciences, Belgrade, Serbia
27: Also at University of Wisconsin, Madison, USA
28: Also at Mersin University, Mersin, Turkey
29: Also at Izmir Institute of Technology, Izmir, Turkey
30: Also at Kafkas University, Kars, Turkey
31: Also at Suleyman Demirel University, Isparta, Turkey
32: Also at Ege University, Izmir, Turkey
33: Also at Rutherford Appleton Laboratory, Didcot, United Kingdom
34: Also at INFN Sezione di Perugia; Universita di Perugia, Perugia, Italy
35: Also at KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary
36: Also at Istanbul Technical University, Istanbul, Turkey
37: Also at University of Minnesota, Minneapolis, USA
38: Also at Institute for Nuclear Research, Moscow, Russia
39: Also at Texas A&M University, College Station, USA
40: Also at State Research Center of Russian Federation, Institute for High Energy Physics,
Protvino, Russia
31