Abstract

A search is presented for long-lived charged particles that decay within the CMS detector and produce the signature of a disappearing track. A disappearing track is an isolated track with missing hits in the outer layers of the silicon tracker, little or no energy in associated calorimeter deposits, and no associated hits in the muon detectors. This search uses data collected with the CMS detector in 2015 and 2016 from proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC, corresponding to an integrated luminosity of 38.4 fb−1. The results of the search are interpreted in the context of the anomaly-mediated supersymmetry breaking model. The data are consistent with the background-only hypothesis. Limits are set on the product of the cross section for direct production of charginos and their branching fraction to a neutralino and a pion, as a function of the chargino mass and lifetime. At 95% confidence level, charginos with masses below 715 (695) GeV are excluded for a lifetime of 3 (7) ns, as are charginos with lifetimes from 0.5 to 60 ns for a mass of 505 GeV. These are the most stringent limits using a disappearing track signature on this signal model for chargino lifetimes above ≈0.7 ns.

Highlights

  • Background estimation5.1 Charged leptonsThe dominant source of high-pT, isolated tracks from standard model (SM) processes arises from charged leptons from the decay of W or Z bosons or virtual photons

  • A search is presented for long-lived charged particles that decay within the CMS detector and produce the signature of a disappearing track

  • A disappearing track is an isolated track with missing hits in the outer layers of the silicon tracker, little or no energy in associated calorimeter deposits, and no associated hits in the muon detectors

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Summary

The CMS detector

The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter. The silicon tracker measures charged particles within the pseudorapidity range |η| < 2.5 It consists of 1440 silicon pixel and 15 148 silicon strip detector modules and is located in the 3.8 T field of the solenoid. For particles that are not explicitly required to be isolated from other event activity, and that have transverse momentum 1 < pT < 10 GeV and |η| < 1.4, the track resolutions are typically 1.5% in pT and 25–90 (45–150) μm in the transverse (longitudinal) impact parameter. These particles represent the bulk of those produced in collisions. A more detailed description of the CMS detector, together with a definition of the coordinate system used and the relevant kinematic variables, can be found in ref. [19]

Data sets
Event reconstruction and selection
Charged leptons
Spurious tracks
Background estimates
Signal efficiencies
Results
Summary
Full Text
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