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Search for Heavy Stable Charged Particles in pp collisions at sqrt(s)=7 TeV

CMS Collaboration

TL;DR

This work reports a search for Heavy Stable Charged Particles (HSCPs) produced in $pp$ collisions at $\\sqrt{s}=7$ TeV with the CMS detector. Two complementary analyses are employed: a tracker-only approach using high $dE/dx$ and $p_T$, and a tracker-plus-muon approach requiring muon-system compatibility, with HSCP mass inferred from $p$ and $dE/dx$ via a harmonic estimator $I_h$ and the relation $I_h=K\,m^2/p^2+C$. No HSCP signal is observed, and 95% C.L. upper limits are set on gluino and stop pair production under conventional and charge-suppression hadronization scenarios, yielding gluino mass limits up to about 398 GeV/$c^2$ (0.1 fraction) and 311 GeV/$c^2$ (complete charge suppression), with a stop limit around 202 GeV/$c^2$. These are among the most stringent HSCP bounds at the time and inform R-hadron phenomenology and complementary stopped-particle searches.

Abstract

The result of a search at the LHC for heavy stable charged particles produced in pp collisions at sqrt(s) = 7 TeV is described. The data sample was collected with the CMS detector and corresponds to an integrated luminosity of 3.1 inverse picobarns. Momentum and ionization-energy-loss measurements in the inner tracker detector are used to identify tracks compatible with heavy slow-moving particles. Additionally, tracks passing muon identification requirements are also analyzed for the same signature. In each case, no candidate passes the selection, with an expected background of less than 0.1 events. A lower limit at the 95% confidence level on the mass of a stable gluino is set at 398 GeV/c^2, using a conventional model of nuclear interactions that allows charged hadrons containing this particle to reach the muon detectors. A lower limit of 311 GeV/c^2 is also set for a stable gluino in a conservative scenario of complete charge suppression, where any hadron containing this particle becomes neutral before reaching the muon detectors.

Search for Heavy Stable Charged Particles in pp collisions at sqrt(s)=7 TeV

TL;DR

This work reports a search for Heavy Stable Charged Particles (HSCPs) produced in collisions at TeV with the CMS detector. Two complementary analyses are employed: a tracker-only approach using high and , and a tracker-plus-muon approach requiring muon-system compatibility, with HSCP mass inferred from and via a harmonic estimator and the relation . No HSCP signal is observed, and 95% C.L. upper limits are set on gluino and stop pair production under conventional and charge-suppression hadronization scenarios, yielding gluino mass limits up to about 398 GeV/ (0.1 fraction) and 311 GeV/ (complete charge suppression), with a stop limit around 202 GeV/. These are among the most stringent HSCP bounds at the time and inform R-hadron phenomenology and complementary stopped-particle searches.

Abstract

The result of a search at the LHC for heavy stable charged particles produced in pp collisions at sqrt(s) = 7 TeV is described. The data sample was collected with the CMS detector and corresponds to an integrated luminosity of 3.1 inverse picobarns. Momentum and ionization-energy-loss measurements in the inner tracker detector are used to identify tracks compatible with heavy slow-moving particles. Additionally, tracks passing muon identification requirements are also analyzed for the same signature. In each case, no candidate passes the selection, with an expected background of less than 0.1 events. A lower limit at the 95% confidence level on the mass of a stable gluino is set at 398 GeV/c^2, using a conventional model of nuclear interactions that allows charged hadrons containing this particle to reach the muon detectors. A lower limit of 311 GeV/c^2 is also set for a stable gluino in a conservative scenario of complete charge suppression, where any hadron containing this particle becomes neutral before reaching the muon detectors.

Paper Structure

This paper contains 7 sections, 3 equations, 3 figures, 3 tables.

Table of Contents

  1. Introduction
  2. The CMS Detector
  3. Candidate Selection and Background Estimation
  4. Results
  5. Conclusions
  6. Acknowledgements
  7. The CMS Collaboration

Figures (3)

  • Figure 1: Normalized distributions of $p_{\mathrm{T}}$ (left) and $I_{as}$ (right) in data and two MC samples, for candidates passing the tracker-only pre-selection. The two MC samples contain events from QCD processes and from pair-production of $\mathrm{\widetilde{g}}$ with a mass of 200 GeV/$c^2$, respectively.
  • Figure 2: Mass spectrum for the loose selection defined in Table \ref{['tab:selectioneff']} for the tracker-plus-muon (left) and tracker-only (right) candidates. Shown are: observed spectrum (black dots with the error bars), data-based predicted background spectrum (red triangles) with its uncertainty (green band) and the spectrum predicted by MC for a signal of pair-produced stable $\mathrm{\widetilde{g}}$ with a mass of 400 (left) and 300 (right) GeV/$c^2$ (blue histogram).
  • Figure 3: Predicted theoretical cross section and observed 95% C.L. upper limits on the cross section for the different combinations of models and scenarios considered: pair production of supersymmetric stop and gluinos; different fractions, $f$, of $R$-gluonball states produced after hadronization and charge suppression ("ch. suppr.") scenarios. Only the results obtained with the most sensitive selection are reported: tracker-only for the charge suppression scenarios and tracker-plus-muon for all other cases. The bands represent the theoretical uncertainties on the cross section values.