CMS-EXO-15-010

CMS-EXO-15-010 ; CERN-EP-2016-204
Search for long-lived charged particles in proton-proton collisions at $\sqrt{s}=$ 13 TeV
CMS Collaboration
27 September 2016
Phys. Rev. D 94 (2016) 112004
Abstract: Results are presented of a search for heavy stable charged particles produced in proton-proton collisions at $\sqrt{s} =$ 13 TeV using a data sample corresponding to an integrated luminosity of 2.5 fb$^{-1}$ collected in 2015 with the CMS detector at the CERN LHC. The search is conducted using signatures of anomalously high energy deposits in the silicon tracker and long time-of-flight measurements by the muon system. The data are consistent with the expected background, and upper limits are set on the cross sections for production of long-lived gluinos, top squarks, tau sleptons, and lepton-like long-lived fermions. These upper limits are equivalently expressed as lower limits on the masses of new states; the limits for gluinos, ranging up to 1610 GeV, are the most stringent to date. Limits on the cross sections for direct pair production of long-lived tau sleptons are also determined.
Links: e-print arXiv:1609.08382 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Distribution of the ${ {\mathrm {d}}E/ {\mathrm {d}}x}$ estimator, ${I_{\mathrm {h}}}$ (see Section 3.1), versus particle momentum for tracks in the 13 TeV data, and for simulation of HSCP for singly or multiply charged particles with masses of 400 and 1000 GeV. The vertical scale shows the density of entries for data only.
png pdf	Figure 2: Observed and predicted mass spectra for loose selection candidates in the tracker-only (left) and tracker+TOF (right) analyses. The expected distributions for representative signals are shown as histograms.
png pdf	Figure 2-a: Observed and predicted mass spectra for loose selection candidates in the tracker-only analysis. The expected distributions for representative signals are shown as histograms.
png pdf	Figure 2-b: Observed and predicted mass spectra for loose selection candidates in the tracker+TOF analysis. The expected distributions for representative signals are shown as histograms.
png pdf	Figure 3: Observed and predicted mass spectra for candidates passing the final selection in the tracker-only (left) and tracker+TOF (right) analyses. The expected distributions for representative signals are shown as histograms.
png pdf	Figure 3-a: Observed and predicted mass spectra for candidates passing the final selection in the tracker-only analysis. The expected distributions for representative signals are shown as histograms.
png pdf	Figure 3-b: Observed and predicted mass spectra for candidates passing the final selection in the tracker+TOF analysis. The expected distributions for representative signals are shown as histograms.
png pdf	Figure 4: Results of the HSCP search as the cross section upper limits at 95% CL for various signal models for the tracker-only analysis (left) and tracker+TOF analysis (right) at $\sqrt {s} =$ 13 TeV. In the legend, ``CS'' stands for charge-suppressed interaction model.
png pdf	Figure 4-a: Results of the HSCP search as the cross section upper limits at 95% CL for various signal models for the tracker-only analysis at $\sqrt {s} =$ 13 TeV. In the legend, ``CS'' stands for charge-suppressed interaction model.
png pdf	Figure 4-b: Results of the HSCP search as the cross section upper limits at 95% CL for various signal models for the tracker+TOF analysis at $\sqrt {s} =$ 13 TeV. In the legend, ``CS'' stands for charge-suppressed interaction model.

Tables
png pdf	Table 1: Selection criteria for the two analyses with the number of predicted and observed events. In the background prediction, the statistical and systematic uncertainties are added in quadrature.
png pdf	Table 2: Systematic uncertainties for the two HSCP searches. All values are relative uncertainties in the signal acceptance for the tracker-only and tracker+TOF analyses.
png pdf	Table 3: Summary of the search for long-lived gluinos: the $ {p_{\mathrm {T}}} $ (GeV), $ {I_{\mathrm {as}}} $, $ {1/\beta } $, and mass thresholds M (GeV) requirements, the predicted and observed yields passing these criteria, and the resulting expected (exp.) and observed (obs.) cross section limits. The signal efficiencies and theoretical (theo.) cross sections are also listed.
png pdf	Table 4: Summary of the search for long-lived top squarks: the $ {p_{\mathrm {T}}} $ (GeV), $ {I_{\mathrm {as}}} $, $ {1/\beta } $, and mass thresholds M (GeV) requirements, the predicted and observed yields passing these criteria, and the resulting expected (exp.) and observed (obs.) cross section limits. The signal efficiencies and theoretical (theo.) cross sections are also listed.
png pdf	Table 5: Summary of the search for long-lived tau sleptons: the $ {p_{\mathrm {T}}} $ (GeV), $ {I_{\mathrm {as}}} $, $ {1/\beta } $, and mass thresholds M (GeV) requirements, the predicted and observed yields passing these criteria, and the resulting expected (exp.) and observed (obs.) cross section limits. The signal efficiencies and theoretical (theo.) cross sections are also listed.
png pdf	Table 6: Summary of the search for long-lived particles from modified Drell-Yan models of various charge: the $ {p_{\mathrm {T}}} $ (GeV), $ {I_{\mathrm {as}}} $, $ {1/\beta } $, and mass thresholds M (GeV) requirements, the predicted and observed yields passing these criteria, and the resulting expected (exp.) and observed (obs.) cross section limits. The signal efficiencies and theoretical (theo.) cross sections are also listed.
png pdf	Table 7: Mass limits obtained at $\sqrt {s}=$ 13 TeV for various HSCP candidate models compared with earlier results for $\sqrt {s}= $ 7+8 TeV [26]. In the model name, ``CS'' stands for charged suppressed interaction model and ``DY'' for Drell-Yan. The limits for doubly charged particles are also compared to the earlier CMS results obtained with the `multiply charged' analysis, which was specifically designed to search for multiply charged particles.

Summary

A search for heavy stable charged particles produced in proton-proton collisions at $\sqrt{s}= $ 13 TeV using the CMS detector is presented. Two complementary analyses were performed: using only the tracker and using both the tracker and the muon system. The data are found to be compatible with the expected background. Mass limits for long-lived gluinos, top squarks, tau sleptons, and multiply charged particles are calculated. The models for $R$-hadron-like HSCPs include a varying fraction of $ \tilde{\gamma} $-gluon hadronization and two different interaction models leading to a variety of exotic experimental signatures. The limits are significantly improved over those from Run 1 of the LHC, and the limits on long-lived gluinos, ranging up to 1610 GeV, are the most stringent to date.

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