CMS PAPER CFT-09-010 CMS Paper arXiv:0911.4045v2 [physics.ins-det] 5 Jan 2010 2009/12/29 Performance Study of the CMS Barrel Resistive Plate Chambers with Cosmic Rays The CMS Collaboration∗ Abstract In October and November 2008, the CMS collaboration conducted a programme of cosmic ray data taking, which has recorded about 270 million events. The Resistive Plate Chamber system, which is part of the CMS muon detection system, was successfully operated in the full barrel. More than 98 % of the channels were operational during the exercise with typical detection efficiency of 90 %. In this paper, the performance of the detector during these dedicated runs is reported. ∗ 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 collisions between protons delivered by the Large Hadron Collider (LHC) [2]. The Resistive Plate Chamber (RPC) system [3] is part of the muon detection system and is used for triggering purposes. RPCs have been chosen because of their good time resolution (about 2 ns) and high granularity, which permit a fast and efficient triggering of muons over large areas. During October-November 2008, the CMS Collaboration conducted a month-long data-taking exercise known as the Cosmic Run At Four Tesla (CRAFT), with the goal of commissioning the experiment for extended operation [4]. With all installed detector systems participating, CMS recorded 270 million cosmic-ray-triggered events with the solenoid at a central flux density of 3.8 T. The muon system is composed of a central barrel (in the pseudo-rapidity window |η | < 1.04) and two closing endcaps (1.04 < |η | < 2.4). The RPCs participated in the CRAFT data taking with the full barrel and half of the endcaps in operation. Part of the endcaps was not operational because the readout electronics was not yet available. For the RPC system, the CRAFT 2008 exercise has permitted the check of the full data taking chain, from the detector up to the data acquisition boards, and the confirmation of the detector performance established during the quality control phase [5], also in presence of the CMS magnetic field. The exercise was also a useful benchmark to complete the commissioning of the endcap part of the RPC system. This paper is focused on the barrel RPC system performance. Sections 2 and 3 describe the RPC system layout, and the operation and monitoring procedures during the CRAFT exercise, respectively. In Section 4, the readout electronics is presented and the synchronization procedure is described. Section 5 deals with the barrel RPC performance, in terms of cluster size, position resolution and detection efficiency. 2 RPC system layout The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter. The silicon pixel and strip tracker, the crystal electromagnetic calorimeter (ECAL) and the brass-scintillator hadronic calorimeter (HCAL) are located within the solenoidal field volume. Muons are measured in gas ionization detectors embedded in the steel return yoke. CMS uses a right-handed coordinate system, with the origin at the nominal collision point, the x-axis pointing to the centre 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, the azimuthal angle, φ, is measured in the x-y plane. The RPC detectors are employed in CMS as a dedicated trigger system in both the barrel and in the endcap regions. They complement the muon tracking system: drift tubes (DT) [6] in the barrel and cathode strip chambers (CSC) [7] in the endcaps. From the geometrical point of view, the muon system is divided into five wheels in the barrel and three disks in each endcap. Each barrel wheel is divided in 12 sectors, covering the full azimuthal dimension (see Fig. 1). Each sector consists of four layers of DTs and six layers of RPCs, with a total of 480 RPC stations of average area of 12 m2 . The two innermost DT layers are sandwiched between RPC layers (RB1in and RB1out for the innermost DT layer, RB2in and 2 2 RPC system layout RB2out for the second one). The third and fourth DT layers are complemented with a single RPC layer, placed on their inner side (RB3 and RB4). A detailed description of the muon system geometry can be found in Ref. [1]. Figure 1: Transverse view of the muon system layout in the barrel region, showing the positions of the DT and RPC stations. Each barrel RPC station is mechanically composed of two or three adjacent RPC units, called “rolls”, making a total of 1020 rolls for the barrel RPC system. Figure 2 shows a schematic layout of a RPC station composed by two rolls. The CMS RPC rolls are double RPC units, where each unit is composed of two bakelite electrodes, each 2 mm thick, and a 2 mm wide gas gap. Readout strips, which are oriented along the beam direction, are placed between the two RPC units, with an independent electronic channel for each strip. The total readout system of the barrel RPC detector consists of 68 136 channels. The strip location defines a point in the local reference frame of the RPC with a precision given by the strip width, ranging from 2.3 cm, for the innermost RB1in layer, to 4.1 cm, for the RB4 layer (see Table 1). The strip signals are discriminated and shaped into 100 ns digital pulses by front-end boards with programmable discriminator thresholds. The RPC detectors, which work in saturated avalanche mode, use a three-component, nonflammable gas mixture composed of 96.2 % C2 H2 F4 (R134a), 3.5 % isobutane (C4 H10 ) and 0.3 % SF6 . Water vapour is added to obtain a mixture with a relative humidity of 40–50 %, in order to maintain a constant bakelite resistivity and, thus, avoid a degradation of RPC performance under high background conditions. The large volume of the total RPC system (18 m3 ) and the use of a rather expensive gas mixture impose the use of a gas recirculation system. This system consists of the following modules: the primary supply, the mixer, the humidifier, the closedloop circulators, the gas distributors to the chambers, the purifiers, and the pump. The purifier 3 Figure 2: Schematic layout of a RPC station composed of two rolls. system is made of a set of filters designed to remove contaminants from the gas mixture. The system operates with a fraction of fresh gas mixture in the range from 10 % to 2 %. This is the first time that such a large RPC system is operated with a closed loop gas system. 3 Detector operation and monitoring The effective working voltage, Veff , relevant for the charge avalanche production inside the RPC, depends on environmental parameters such as gas temperature (T) and pressure (P), according to Eq. 1 [8] Veff = V × P0 T × P T0 , (1) where Veff is the effective voltage, V is the applied power voltage, and P0 = 1010 mbar and T0 = 293 K are the reference pressure and temperature, respectively. Only the effective voltage is relevant when comparing detector performance in different sites and run conditions. The CMS RPCs have been extensively tested at the production sites and their physics performance was studied [3, 5]. During 2006, a small fraction of the RPC system was calibrated and operated [9]. In both cases, it was found that 95 % of the maximum plateau efficiency is reached at an effective voltage of 9.6 kV, corresponding to an average applied voltage of 9.2 kV for the pressure conditions in the CMS cavern. For the CRAFT 2008 exercise, the operating voltage was set to 9.2 kV and the electronic thresholds of the readout system were set to 230 mV, corresponding to an induced charge of 180 fC. These operating conditions are conservative and do not permit the detector to reach its maximum efficiency. This approach was chosen to maintain low noise levels and safe operating conditions, since this was the first time that the full system was operated. Following extensive past studies [10], the working conditions were maintained within strict ranges: temperature lower than 24 ◦ C, humidity in the range 40–50 % and fraction of O2 below 300 ppm. These parameters were monitored and controlled by the Detector Control System (DCS) [11]. Their values were stored in a database and used, offline, to study the system stability. 4 3.1 3 Detector operation and monitoring Temperature Entries 40 35 310 Mean 21.72 RMS 0.701 30 CMS 2008 25 temperature [°C] # of chambers/ 0.2 °C Out of the 480 RPC stations, 310 are equipped with a temperature probe installed inside the mechanical frame. Figure 3 shows in the left plot the temperature distribution of those barrel stations at the end of the CRAFT period (averaged over one day) and on the right plot its average vs. time. The system temperature was maintained below 24 ◦ C during the full CRAFT period, in order to guarantee proper RPC operation. Clear variations are observed when the electronics of CMS is switched on or off. The steep increase seen at the start of the CRAFT exercise, when all the detectors were fully operating, is a consequence of the non optimized cooling of the system. A special effort was dedicated to increase the cooling circuit capability after the end of the CRAFT exercise. The temperature of the input cooling water has been reduced by one degree in order to guarantee a constant stable temperature lower than 24 ◦ C, as confirmed in 2009, during long cosmic rays data taking periods. 30 28 24 20 22 15 20 10 18 5 0 15 CMS 2008 26 16 16 17 18 19 20 21 22 23 24 25 temperature [°C] 16.10.08 23.10.08 30.10.08 06.11.08 date Figure 3: RPC temperature, as measured by the probes installed inside the stations. Left side: distribution of RPC temperature taken at the end of the CRAFT period and averaged over one full day of data taking. Right side: Average RPC temperature as a function of time. Each point represents the temperature averaged over 4 hours and over all barrel stations. The increase and the variations of the temperature are triggered by the start of the CMS electronics. 3.2 Currents The currents drawn by the RPCs, I, are strongly affected by variations of the environmental conditions. A sudden current increase could also indicate a malfunctioning of the detector. Therefore, a careful and continuous monitoring of the currents is performed. Each RPC station is powered by a separate high voltage supply. The current drawn in each RPC station is read out and stored through the DCS. Figure 4 shows in the left plot the I distribution at an operating voltage of 9.2 kV, for the 480 barrel stations, at the end of the CRAFT period. Only for 11 stations the value of I is larger than 3 µA. During the CRAFT exercise, ten units out of 2040 were disconnected because of problems with the high voltage connections, leaving the corresponding rolls working in single gap mode. Figure 4 right plot shows that the average current drawn by the stations was around 1 µA and stable in time. No correlation is observed between the mean current values and the temperature variations, in the operating range. 3.3 Counting rates The RPC noise rate is carefully monitored, since abnormal values in some parts of the detector can result in high fake muon trigger rates. At the beginning of each run, dedicated calibration data were taken and analysed to identify and mask noisy readout channels with rates above 5 Entries 90 80 480 Mean 0.9323 RMS 0.9803 70 60 50 current [µA] # of chambers/ 0.2 µA 3.4 Gas monitoring 3 2.5 CMS 2008 2 1.5 CMS 2008 40 1 30 20 0.5 10 0 0 1 2 3 4 5 6 7 8 9 10 current [µA] 0 16.10.08 23.10.08 30.10.08 06.11.08 date Figure 4: Distribution of the current drawn by the RPCs. Left plot shows the average over one full day of data taking at the end of the CRAFT period. The plot has no overflow. Right plot: average current as a function of time. Each point is the average current over 4 hours and over all barrel stations. The operating voltage is 9.2 kV. 100 Hz/cm2 . This value was chosen because it corresponds to the limit that the trigger system can sustain. The total number of masked and dead channels was stable during the CRAFT period, at about 1 % of the total number of channels in both cases. The average noise per second and per cm2 is computed for each roll by adding the contributions from all non-masked channels. The distribution of the number of rolls as a function of the average noise is shown in Fig. 5, for one specific run. Only 3 % of the rolls have an average noise rate greater than 1 Hz/cm2 . Although the average noise rate is very low, a problem related to events with correlated noise on several layers has been detected few times per day affecting about 10−3 of the total data taking time during the CRAFT exercise. A special effort has been made to understand the sensitivity of the RPCs to external noise sources. The detector grounding has been improved where possible, and further studies are in progress. Preliminary analyses have demonstrated that the fake trigger rate is reduced by two orders of magnitude when the LHC trigger algorithm is used instead of the dedicated cosmic ray trigger employed during the CRAFT exercise. The LHC trigger algorithm requires more stringent constraints on the incoming muon direction and is less sensitive to the detector noise. 3.4 Gas monitoring The mixture composition and its quality are monitored by two independent devices. The Gas Quality Monitor [12, 13] performs chemical analyses (mainly gas chromatography, pH and fluoride monitoring). The Gas Gain Monitor [14], is based on the monitoring of the performance of three sets of 50 × 50 cm2 single gap RPCs, each supplied with a different gas mixture (fresh gas, and gas from the recirculating system, before and after the purifiers). During the CRAFT exercise, the gas system was operated continuously with a fraction of 8 % of fresh mix. The lifetime of the purifiers before regeneration was about 36 hours between regenerations of first stage purifier, to remove water from gas mixture humidity, and one week between regenerations of second stage purifier, to remove air contamination. The full system was running smoothly during the operation. The downtime due to gas system stops was less than 1 %. 6 number of rolls/0.01 Hz/cm2 4 Entries Mean RMS 102 Synchronization of RPC data 1020 0.72 5 CMS 2008 10 1 10-2 10-1 1 102 10 noise rate (Hz/cm2) Figure 5: Example distribution of the number of rolls as a function of the average noise in the roll, for a given data taking run. Channels exceeding 100 Hz/cm2 are masked and do not contribute to the average noise. The operating voltage is 9.2 kV. 4 Synchronization of RPC data Muon signals detected by the RPC chambers and transmitted by the readout electronics must arrive in dedicated electronic boards at a specified time, in order to correctly contribute to the trigger decisions. In addition, RPC data sent to the CMS Data Acquisition system (DAQ) and RPC trigger information must be associated to the right LHC bunch crossing (BX: 25 ns time interval). The different steps of data transmission in the RPC system are described in detail in Ref. [15]. After pulse discrimination in the front end boards, the data are transmitted asynchronously to the Link Boards situated on the CMS detector, where zero-suppression is performed. The data are then sent through optical fibres to the CMS counting room, in the underground cavern, where RPC muon trigger objects are identified, as part of the CMS Level-1 trigger system, and sent to the Global Muon Trigger. In parallel, the data are sent to the CMS DAQ system. To ensure integration with CMS, the RPC readout and trigger systems work in synchronous mode using the CMS Timing, Trigger and Control (TTC) system [16]. The TTC signals (including clock and reference bunch crossing identification) are distributed to the Link Boards, where the signals from the detector are synchronized with the LHC clock. The data are assigned to the proper bunch crossing according to a time window determined by the length of the TTC fibres, the muon time of flight, and the signal propagation and transmission times along the strips, cables and electronics. The RPC readout [17] is designed to send data from up to 8 consecutive bunch crossings (BXs) to the DAQ system: the trigger BX plus 3 pre- and 4 post-trigger BXs. During the CRAFT exercise, only 7 BXs were transmitted to the DAQ (±3 BXs around the triggered event). The timing setups of the system are different for the LHC beam mode and for the cosmic ray 7 runs. In beam mode the synchronization is driven by beam collisions, which are fixed in phase with respect to the LHC clock, while in the cosmic mode this phase is arbitrary: cosmic rays arrive randomly with respect to the LHC clock. The synchronizations of the upper and lower parts of the detector differ significantly in the two modes, due to the asymmetric phi distribution of the cosmic rays. In order to optimize the data synchronization, initial delays were estimated, based on the length of cables and fibres. The bottom-central part of the detector was chosen as a reference, and delays of data from other parts of the detector were fine-tuned to optimize the data alignment in time. The same timing was kept for the full CRAFT period. As an illustration of the RPC synchronization during the CRAFT exercise, Fig. 6 presents a typical example of the time distribution of the data coming from individual RPCs. The time is counted with respect to the bunch crossing assigned by the RPC Level-1 global trigger logic, based on the coincidence of at least 3 chambers along a muon trajectory. The peak in the central bin corresponds to data which are synchronous with the RPC Level-1 trigger. The spread to the two neighbouring bins is caused mainly by the arbitrary choice of the synchronization phase, relevant only for cosmic ray runs. The spread over the other bins is due to the non-perfect synchronization of contributing triggers, and to a background caused by Link Boards connected to the most noisy electronic channels. ×10 entries 3 450 Cosmic data 400 Contribution from most noisy channels 350 300 CMS 2008 250 200 150 100 50 0 -3 -2 -1 0 1 2 3 bunch crossing (25 ns units) Figure 6: Typical time distribution (in bunch crossing units of 25 ns) of the data coming from individual RPCs with respect to the RPC global trigger time. The dashed line shows the background caused by the 10 over 1020 Link Boards connected to the most noisy channels. In view of the good quality of the present data, much better synchronization is expected for LHC runs. 5 Detector performance The performance of the RPC system has been studied by making use of the local DT hit reconstruction [6]. The three innermost DT layers are able to locally reconstruct three dimensional muon track segments with up to eight hits in the rφ plane and up to four hits in the rz plane. 8 5 Detector performance The outermost DT layer provides a segment in the rφ plane. The extrapolation of a DT track segment onto an RPC plane allows the study of the local RPC performance, by searching for RPC channels over threshold in a small region around the impact point. Previous studies [9] have shown that a range of ± 2 strips between the extrapolated impact point and the closest firing strip is adequate. In addition, the CRAFT exercise led to the identification of 15 swapped readout cables out of a total of 4720, and a few cases of RPC to DT misalignments at the level of more than 1 cm. In the following sub-sections the results on cluster size, position resolution and detection efficiency are reported for the whole barrel system. The RPC cluster size and the position resolution are studied separately for layers with different strip pitches. No special selection is applied to the DT track segments used for the extrapolation, except for the requirement that no other segment is reconstructed in the DT station. This condition is imposed to reject multiple muon events and other possible ambiguous topologies. Moreover, only pointing segments in the rφ plane have been used in these analyses. A pointing track segment in the rφ plane is defined as a segment within an angle of ± 20 degrees around the normal to the RPC layer, in the plane perpendicular to the strip direction. All the figures have been produced by analysing a run of about 2 million events, representative of the full CRAFT period. 5.1 Cluster size A cluster is defined as a consecutive set of strips, each of them collecting an induced charge above the discrimination threshold of 180 fC. The number of strips in the cluster is called the cluster size. The cluster size depends on the RPC strip pitch, on the impact point position with respect to the strip, and on the track crossing angle. Figure 7 shows the cluster size distribution for the RB1in layers, for pointing muons. The different strip pitches and the average cluster sizes are given for all layers in Table 1. The fractions of events having cluster sizes corresponding to 1, 2, 3 or more than 3 strips are shown for different layers in Fig. 8. Table 1: Strip pitch and average cluster size, counted as the number of strips, for pointing track segments, with operating voltage of 9.2 kV. RPC layer strip pitch (cm) average cluster size RB1in 2.3 1.52 RB1out 2.5 1.46 RB2in 2.8 1.41 RB2out 3.0 1.38 RB3 3.5 1.31 RB4 4.1 1.25 The number of firing strips for a crossing muon is a function of the local impact point position with respect to the RPC strip. The distribution in Fig. 9 shows the deviation, ∆, measured in strip pitch units, between the impact point and the cluster centre for the RB1in layer, in a local reference frame. In this local frame the fired strip is between 0 and 1 for events with cluster size of 1, the two fired strips are between −1 and 1 for events with cluster size of 2, and the three fired strips are between −1 and 2 for events with cluster size of 3. The three distributions, normalized to the same area, are overlayed. Events with cluster size of 1 are more frequent for tracks crossing the RPC layer close to the middle of a strip, while the fraction of events with a cluster size of 2 increases for muons close to the edge between two adjacent strips. 9 fraction 5.1 Cluster size Entries 3319060 0.6 Mean 1.52 RMS 0.843 0.5 CMS 2008 0.4 0.3 0.2 0.1 0 1 2 3 4 5 6 7 8 9 10 cluster size fraction Figure 7: Normalized distribution of the cluster size for the RB1in layer, for pointing track segments. cluster size 1 cluster size 2 cluster size 3 cluster size >3 1 0.8 CMS 2008 0.6 0.4 0.2 0 RB1 in (2.3 RB1 RB2 RB2 RB4 RB3 (4.1 (3.5 ou ( in (2. 8 cm out (3.0 c cm) cm) cm) t 2.5 cm m ) ) ) RPC layer Figure 8: Relative population of reconstructed clusters with size equal to 1, 2, 3 and more than 3 strips, for each RPC layer. 10 5 Detector performance In addition, the cluster size depends on the muon incident angle with respect to the RPC surface, in the plane orthogonal to the strip direction. This is visible in Fig. 10, which presents the dependence of the average cluster size on the absolute value of the tangent of the angle α, defined as the angle between the muon direction and the normal to the RPC surface in the plane perpendicular to the strip direction, for the RB1in layer. This dependence is due both to the increased path length in the crossed gas gap and to the RPC double gap structure where two independent avalanches develop in the two gas gaps, 6 mm apart, which may induce signals on different strips, increasing the cluster size. arbitrary units It should be noted that, because of the bending of muon trajectories due to the magnetic field, low momentum muons coming from the interaction point, during LHC runs, may cross the RPC detectors with relatively large angles. Cosmic muons are very useful to study these topologies since they cross the detector at all possible angles, depending on the sector. cluster size 1 cluster size 2 cluster size 3 0.025 CMS 2008 CMS 2008 0.02 0.015 0.01 0.005 0 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 segment impact point (strip pitch) strip cluster size 1 strips cluster size 2 strips cluster size 3 Figure 9: Distribution of the track impact point for the RB1in layer in a local reference frame, for events with cluster size of 1, 2 and 3, in units of strip pitch. The local frame, described by the drawing under the plot, is defined in such a way that the fired strip is between 0 and 1 for events with cluster size of 1, the two fired strips are between −1 and 1 for events with cluster size of 2, and the three fired strips are between −1 and 2 for events with cluster size of 3. The three distributions are normalized to the same unit area. 5.2 Position resolution The centre of a cluster provides a measurement of the position of the muon track crossing point, in the rφ plane. In order to study the RPC position resolution, the cluster centre is compared to the extrapolated point of the DT segment onto the RPC layer. The distribution of the off-set between the position of the track crossing point onto the surface separating the two gaps and the cluster centre, named residual, is computed for every roll, providing an estimate of the relative DT and RPC alignment. 11 average cluster size 5.3 Detection efficiency 2.8 2.6 CMS 2008 2.4 2.2 2 1.8 1.6 1.4 0 1 2 3 4 5 |tan α | Figure 10: Average cluster size as a function of the absolute value of the tangent of the angle α, defined as the angle between the track direction and the normal to the RPC surface in the plane perpendicular to the strip direction, for the RB1in layer and with an operating voltage of 9.2 kV. Figure 11 presents the distribution of the mean value of the residuals for all barrel rolls. The relative alignment is of a few millimetres, but two cases of a few centimetres have also been observed (not visible on the plot scale). The mean values extracted from the residual distributions have been used to correct the data offline, in order to improve the position resolution. Figure 12 shows the residual distribution in cm for the RB1in layer, after having applied the alignment corrections, for events with cluster size lower than four. The analysis of the RPC residuals has been performed for all layers, corresponding to different strip pitches as reported in Table 1, and for events with different cluster sizes. The RMS values of the residual distribution are presented in Fig. 13, as a function of the layer, for different cluster sizes. The trend reflects the variation of the strip pitch and the geometry of the different RPC layers. 5.3 Detection efficiency The most important parameter defining the RPC performance is the detection efficiency. The DT segment extrapolation, presented at the beginning of Section 5, is used to estimate the RPC efficiency, for a full roll. For each DT track segment extrapolated onto the RPC surface, a roll is considered efficient if at least one RPC strip is over threshold within ± 2 strips from the extrapolated impact point. Figure 14 shows the efficiency vs. the local impact point on the RPC surface. The pattern due to the spacers placed on a 10 × 10 cm2 grid is clearly visible. Moreover, a reduction of the overall efficiency is visible in the y coordinate (as defined in the figure) at about 55 cm, where only one gap is present. The roll efficiency distribution is shown in Fig. 15 for a typical run, taken at the operating volt- 12 number of rolls/0.1 cm 5 Entries 200 Detector performance 1020 Mean -0.0039 RMS 0.21 CMS 2008 150 100 50 0 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 residual mean value (cm) fraction/0.25 cm Figure 11: Normalized distribution of the mean value of the residuals in cm, for all the RPC rolls. Two entries are out of the range. Entries 3234989 0.09 0.08 Mean RMS CMS 2008 -0.007 0.89 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 -10 -8 -6 -4 -2 0 2 4 6 8 10 residual (cm) Figure 12: Normalized distribution of the residuals in cm, for the RB1in layer (events with cluster size larger than three are not included). RMS residuals (cm) 13 2 overall cluster size 1 cluster size 2 cluster size 3 1.8 1.6 CMS 2008 1.4 1.2 1 0.8 0.6 RB1 in (2.3 RB2 RB1 RB2 RB4 RB3 (4.1 (3.5 ou ( in (2. 8 cm out (3.0 c cm) c cm) t 2.5 cm m m) ) ) ) RPC layer Figure 13: RMS of the distributions of the residuals, for the different layers (corresponding to different strip pitches) and for different cluster sizes. age of 9.2 kV. The peak of the distribution is about 90 %, while the tail at lower efficiency values is due to now known swapped cables, chambers working in single gap mode and chambers with synchronization problems. After the end of the CRAFT exercise many improvements have been obtained and the operating conditions have been optimized. In 2009 the efficiency distribution was around 95 % at 9.4 kV. 6 Conclusions Data collected during the CRAFT 2008 period have been very useful for detector commissioning. About 98 % of the electronic channels were operational during the exercise. Hardware problems such as swapped cables and electronic failures have been identified and fixed. The relative position of each RPC station with respect to the DT chambers has been measured in the rφ direction, and the position resolution of the RPC system has been determined. Software tools to monitor the system performance have been developed and tuned during the running period. The performance of the barrel system has been measured from data. The results show a good stability of the detector and an efficiency around 90 % at the operating voltage of 9.2 kV. Many improvements have been made after the CRAFT 2008 exercise. The temperature of the input cooling water has been reduced by one degree. Hardware failures have been fixed, the working voltage and the electronic threshold have been optimized, and the synchronization of the RPC barrel signals has been improved. Although more systematic studies are still in progress, the RPC barrel system is ready for LHC beam collisions. 14 6 Conclusions y (cm) y 12 x 24 spacers per roll every 10 cm X X (cm) Gas gap Gas gap Forward roll Gas gap Gas gap Single gap working region RPC Up RPC Down Backward roll Figure 14: Efficiency of an RB1in roll as a function of the x and y coordinates (as defined in the figure) of the extrapolated track impact point. The lower efficiency spots are due to the dead regions induced by spacers on a 10 × 10 cm2 grid. An efficiency reduction is also visible for the y coordinate at about 55 cm, where only a single gap is present. 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); Academy of Finland, ME, and HIP (Finland); CEA and CNRS/IN2P3 (France); 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); MICINN 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. number of rolls 15 250 200 Entries CMS 2008 1020 Mean 86.29 RMS 14.61 150 100 50 0 10 20 30 40 50 60 70 80 90 100 efficiency (%) Figure 15: Efficiency distribution for barrel rolls, at an operating voltage of 9.2 kV. The tail at lower efficiency values is due to now known swapped cables, chambers working in single gap mode and chambers with synchronization problems. References [1] CMS Collaboration, “The CMS experiment at the CERN LHC”, JINST 3 (2008) S08004. doi:10.1088/1748-0221/3/08/S08004. [2] L. Evans and P. Bryant (eds.), “LHC machine”, JINST 3 (2008) S08001. doi:10.1088/1748-0221/3/08/S08001. [3] M. Abbrescia et al., “Cosmic ray tests of double-gap resistive plate chambers for the CMS experiment”, Nucl. Instrum. Meth. A550 (2005) 116–126. doi:10.1016/j.nima.2005.06.074. [4] CMS Collaboration, “The CMS Cosmic Run at Four Tesla”, submitted to JINST (2009). [5] M. Abbrescia et al., “Production and quality control of the barrel RPC chambers of the CMS experiment”, Nucl. Phys. Proc. Suppl. 150 (2006) 290–294. doi:10.1016/j.nuclphysbps.2004.11.389. [6] CMS Collaboration, “Results On Local Muon Reconstruction in DT Chambers From Analysis of Cosmic Muon Data”, submitted to JINST (2009). [7] CMS Collaboration, “CSC performance”, submitted to JINST (2009). [8] M. Abbrescia et al., “Resistive plate chambers performances at cosmic rays fluxes”, Nucl. Instrum. Meth. A359 (1995) 603–609. doi:10.1016/0168-9002(94)01698-4. [9] A. Colaleo et al., “First measurements of the performance of the barrel RPC system in CMS”, Nucl. Instrum. Meth. A609 (2009) 114–121. doi:10.1016/j.nima.2009.07.099. 16 6 Conclusions [10] M. Abbrescia et al., “Long term performance of double gap resistive plate chambers under gamma irradiation”, Nucl. Instrum. Meth. A477 (2002) 293–298. doi:10.1016/S0168-9002(01)01860-5. [11] P. Paolucci and G. Polese, “The Detector Control Systems for the CMS Resistive Plate Chamber”, CMS NOTE 2008/036 (2008). [12] M. Abbrescia et al., “The gas monitoring system for the resistive plate chamber detector of the CMS experiment at LHC”, Nucl. Phys. Proc. Suppl. 177-178 (2008) 293–296. doi:10.1016/j.nuclphysbps.2007.11.133. [13] M. Abbrescia et al., “HF production in CMS-Resistive Plate Chambers”, Nucl. Phys. Proc. Suppl. 158 (2006) 30–34. doi:10.1016/j.nuclphysbps.2006.07.002. [14] L. Benussi et al., “The CMS RPC gas gain monitoring system: an overview and preliminary results”, Nucl. Instrum. Meth. A602 (2009) 805–808, arXiv:0812.1108. doi:10.1016/j.nima.2008.12.175. [15] K. Bunkowski et al., “Synchronization methods for the PAC RPC trigger system in the CMS experiment”, Measur. Sci. Tech. 18 (2007) 2446–2455. doi:10.1088/0957-0233/18/8/020. [16] CMS Trigger/DAQ Group, “CMS L1 Trigger Control system”, CMS NOTE 2002/033 (2002). [17] W. M. Zabolotny et al., “Implementation of the data acquisition system for the resistive plate chamber pattern comparator muon trigger in the CMS experiment”, Measur. Sci. Tech. 18 (2007) 2456–2464. doi:10.1088/0957-0233/18/8/021. 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