Abstract
A search for heavy long-lived multi-charged particles is performed using the ATLAS detector at the LHC. Data collected in 2012 at sqrt{s}=8 TeV from pp collisions corresponding to an integrated luminosity of 20.3 fb^{-1}are examined. Particles producing anomalously high ionisation, consistent with long-lived massive particles with electric charges from |q|=2e to |q|=6e are searched for. No signal candidate events are observed, and 95 % confidence level cross-section upper limits are interpreted as lower mass limits for a Drell–Yan production model. The mass limits range between 660 and 785 GeV.
Highlights
The ATLAS detectorThe ATLAS detector [10] covers nearly the entire solid angle around the collision point
Background estimationThe background contribution to the signal region is estimated using a method which employs sidebands of the two discrim- 362 Page 6 of 23S(MDT dE/dx) S(MDT dE/dx)40 35 30 s = 8 TeV 2520.3 fb-1 20 15 10 CData Mass 600 GeV, z=2 ATLAS D B5 10 15 20 25 30 S(TRT dE/dx)Data Mass 600 GeV, z=3 Mass 600 GeV, z=6 D B
The sub-detector system signatures are different for the two preselected samples, and the final signal regions are chosen differently. They are defined by S(MDT dE/dx) > 5 and S(TRT dE/dx) > 5 for candidates selected as z = 2 and by S(MDT dE/dx) > 7.2 and S(TRT dE/dx) > 6 for candidates selected as z ≥ 3
Summary
The ATLAS detector [10] covers nearly the entire solid angle around the collision point It consists of an inner tracking detector (ID) comprising a silicon pixel detector (pixel), a silicon microstrip detector (SCT) and a transition radiation tracker (TRT). The endcap and forward regions are instrumented with LAr calorimeters for electromagnetic and hadronic energy measurements. The MS is instrumented with tracking detectors designed to measure the momenta of muons that traverse the ATLAS calorimeters. Monitored drift tube (MDT) chambers provide typically 20–25 hits per crossing track in the pseudorapidity range |η| < 2.7, from which a high precision momentum measurement is derived. Chargedparticle trajectories are reconstructed using standard algorithms Since these assume particles have z = 1, the momenta of MCPs are underestimated by a factor z, as the track curvature is proportional to pT/z
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