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Accurate mass determinations in decay chains with missing energy: II

Hsin-Chia Cheng, John F. Gunion, Zhenyu Han, and Bob McElrath
Phys. Rev. D 80, 035020 – Published 25 August 2009
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  • INTRODUCTION
  • CONSTRAINTS COUNTING
  • BASIC EQUATIONS FOR THE TOPOLOGY OF FIG…
  • APPLICATIONS
  • COMPARISON OF SUSY AND UED
  • DISCUSSION AND CONCLUSIONS
  • ACKNOWLEDGEMENTS
  • APPENDICES
    • References

    Abstract

    We discuss kinematic methods for determining the masses of the particles in events at a hadron collider in which a pair of identical particles is produced with each decaying via a series of on shell intermediate beyond-the-standard model (BSM) particles to visible standard model (SM) particles and an invisible particle (schematically, pp→ZZ+jets with Z→Aa→Bba→Ccba→…→cba…+N where a,b,c,… are visible SM particles or groups of SM particles, A,B,C,… are on shell BSM particles, and N is invisible). This topology arises in many models including supersymmetry (SUSY) processes such as squark and gluino pair production and decay. We present the detailed procedure for the case of Z→3  visible particles+N and demonstrate that the masses obtained from the kinematic procedure are independent of the model by comparing SUSY to universal extra dimensions.

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    • Received 20 May 2009

    DOI:https://doi.org/10.1103/PhysRevD.80.035020

    ©2009 American Physical Society

    Authors & Affiliations

    Hsin-Chia Cheng1, John F. Gunion1, Zhenyu Han1, and Bob McElrath2

    • 1Department of Physics, University of California, Davis, California 95616, USA
    • 2CERN, Geneva 23, Switzerland

    See Also

    Accurate Mass Determinations in Decay Chains with Missing Energy

    Hsin-Chia Cheng, Dalit Engelhardt, John F. Gunion, Zhenyu Han, and Bob McElrath
    Phys. Rev. Lett. 100, 252001 (2008)

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    Vol. 80, Iss. 3 — 1 August 2009

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    Images

    • Figure 1
      Figure 1
      A decay chain in SUSY.Reuse & Permissions
    • Figure 2
      Figure 2
      The event topology we consider.Reuse & Permissions
    • Figure 3
      Figure 3
      We plot the number of mass solutions (in 1 GeV bins—the same binning is used for the other plots) vs mass in the ideal case. All possible pairs for 100 events are included. Signal events only.Reuse & Permissions
    • Figure 4
      Figure 4
      Number of mass solutions vs mass after including all combination pairings for 100 events. Signal events only, with only combinatoric ambiguities included.Reuse & Permissions
    • Figure 5
      Figure 5
      Mass solutions with all effects 1–7 included and after cuts I–III for the SPS1a SUSY model and L=300  fb−1. All effects incorporated, including backgrounds.Reuse & Permissions
    • Figure 6
      Figure 6
      For each event, i, and each combination, c, associated with that event, we count the number, Npair(c,i), of events that can pair with it and give at least one solution. The plot shows the frequency of occurrence of different values of Npair(c,i). All effects are incorporated, including backgrounds. The plot is for the SPS1a case (for which the total number of signal+background events is 620 for L=300  fb−1). In the bias-reduction procedure, any choices of c, i yielding Npair(c,i) to the left of the red (dashed) line (corresponding to 75% of the total number of events) are discarded.Reuse & Permissions
    • Figure 7
      Figure 7
      SPS1a, L=300  fb−1 mass difference distributions. All effects incorporated, including backgrounds.Reuse & Permissions
    • Figure 8
      Figure 8
      Final mass distributions after the bias-reduction procedure for the SPS1a SUSY model and L=300  fb−1. All effects incorporated, including backgrounds.Reuse & Permissions
    • Figure 9
      Figure 9
      Mass distributions for 50 events for SPS1a.Reuse & Permissions
    • Figure 10
      Figure 10
      Error bars for mN as a function of the number of background+signal events for SPS1a. All effects and procedures included.Reuse & Permissions
    • Figure 11
      Figure 11
      Final mass distributions before the bias-reduction procedure for the point no. 1 SUSY model and L=100  fb−1. All effects incorporated, including backgrounds.Reuse & Permissions
    • Figure 12
      Figure 12
      Final mass distributions after the bias-reduction procedure for the point no. 1 SUSY model and L=100  fb−1. All effects incorporated, including backgrounds.Reuse & Permissions
    • Figure 13
      Figure 13
      We plot the number of events as a function of mℓ+ℓ− for 600 SPS1a events in 5 GeV bins (after PGS smearing and general cuts, but before the bias-reduction procedure). Only events containing two muons and two electrons with opposite charges are used to avoid ambiguity, each of which contributes two entries to the histogram. The edge at 80 GeV is apparent.Reuse & Permissions
    • Figure 14
      Figure 14
      Dilepton invariant mass distribution for 600 SPS1a events together with 600 point no. 1 events (after PGS smearing and general cuts, but before the bias-reduction procedure). Only events containing two muons and two electrons of opposite charge are used to avoid ambiguity. The two edges at 80 GeV and 157 GeV correspond to SPS1a and point no. 1, respectively.Reuse & Permissions
    • Figure 15
      Figure 15
      The measured mN as a function of the number of background events. The number of signal (SPS1a) events is fixed to 600. In both cases, these are the event numbers after general cuts but before the bias-reduction procedure.Reuse & Permissions
    • Figure 16
      Figure 16
      Final mass distributions for signal events only after employing the bias-reduction procedure for the SPS1a mass choices in the context of the SUSY model and using 400 signal events after PGS smearing and general cuts but before bias reduction. All combinations and solutions are included, but backgrounds associated with the SUSY model are not included.Reuse & Permissions
    • Figure 17
      Figure 17
      Final mass distributions for signal events only after the bias-reduction procedure for the SPS1a mass choices, but in the case of the UED model. The UED event sample is scaled so that there are 400 signal events after PGS smearing and general cuts, but before bias reduction. All combinatorics and solutions are included, but backgrounds associated with the UED model are not included.Reuse & Permissions
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