The performance of the CMS muon detector in proton-proton collisions at √s= 7 TeV at the LHC

Abstract

The performance of all subsystems of the CMS muon detector has been studied by using a sample of proton-proton collision data at √ s = 7 TeV collected at the LHC in 2010 that corresponds to an integrated luminosity of approximately 40 pb −1 . The measured distributions of the major operational parameters of the drift tube (DT), cathode strip chamber (CSC), and resistive plate chamber (RPC) systems met the design specifications. The spatial resolution per chamber was 80-120 µm in the DTs, 40-150 µm in the CSCs, and 0.8-1.2 cm in the RPCs. The time resolution achievable was 3 ns or better per chamber for all 3 systems. The efficiency for reconstructing hits and track segments originating from muons traversing the muon chambers was in the range 95-98%. The CSC and DT systems provided muon track segments for the CMS trigger with over 96% efficiency, and identified the correct triggering bunch crossing in over 99.5% of such events. The measured performance is well reproduced by Monte Carlo simulation of the muon system down to the level of individual channel response. The results confirm the high efficiency of the muon system, the robustness of the design against hardware failures, and its effectiveness in the discrimination of backgrounds. Overview of the muon system Overview of the muon systemThe basic detector process utilized in the CMS muon systems is gas ionization. For all the different technologies-drift tubes, cathode strip proportional planes, and resistive platesthe basic physical modules are called "chambers". The chambers are independently-operating units, which are assembled into the overall muon detector system of CMS. The chambers form part of a spectrometer in which the analyzing magnet is the central solenoid together with the flux return yoke of CMS. To match the cylindrical geometry of the solenoid, the barrel region is instrumented with drift tube chambers, and the 2 endcap regions with cathode strip chambers. Resistive plate chambers are interspersed in both the barrel and endcap regions. The muon chambers must detect the traversing track at several points along the track path to utilize the magnet to measure the deflection of muons as they pass through its field. In the barrel region, this requires chambers to be positioned at several different values of the radial distance R from the beam line, and in the endcap region at several different values of distance along the beam direction z. A "station" is an assembly of chambers around a fixed value of R (in the barrel) or z (in the endcap). There are 4 stations in the barrel and in each endcap (Fig. 1), labeled MB1-MB4 and ME1-ME4, respectively. Along z, the drift tubes and resistive plate chambers in the barrel are divided into 5 "wheels", with Wheel 0 centered at z = 0 and wheels W+1 and W+2 in the +z direction and W-1 and W-2 in the −z direction. Similarly in the R direction in the endcaps, there are "rings" of endcap resistive plate chambers and cathode strip chambers. The latter are labeled ME1/n-ME4/n, where integer n increases with the radia...

Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at √s=13 TeV

“…If no sign is specified, the performance of the + and − stations are combined. The inner ring of the CSC chambers in station 1 has a structure that is different from the other rings; the primary difference is an additional division of ME1/1 into two η partitions called a and b [1]. An overview of the number of chambers per chamber type, number of readout channels, and number of active channels in 2016 is given in Table 1.…”

“…To benefit from this fact, alternate layers in a CSC are staggered by half a strip width, except in the ME1/1 chambers where the strips are narrower and the effect is small. Resolutions are measured separately for the central half of a strip width (σ C ) and the quarter strip-width at each edge (σ E ) [1]. The layer measurements are combined to give an overall resolution σ per CSC station by 1/σ 2 station = 6/σ 2 layer (ME1/1 chambers) and 1/σ 2 station = 3/σ 2 C + 3/σ 2 E (chambers other than ME1/1).…”

Searching in CMS open data for dimuon resonances with substantial transverse momentum

“…Our analysis is based on the DoubleMu primary data set from CMS Run 2011A [13], hereafter referred to as "CMS11a", and benefits from the excellent performance of the CMS muon system [53,54]. We select events that pass the HLT Mu13 Mu8 (µ13µ8) high-level dimuon trigger, which nominally requires p T of 13 (8) GeV for the leading (subleading) muon.…”

Search for resonances in the mass spectrum of muon pairs produced in association with b quark jets in proton-proton collisions at $$ \sqrt{s}=8 $$ and 13 TeV

“…Muons are reconstructed using a simultaneous global fit performed with the hits in the silicon tracker and the muon system. They are required to pass standard identification criteria [54,55] based on the minimum number of hits in each detector, quality of the fit, and the consistency with the primary vertex, by requiring the longitudinal and transverse impact parameters to be less than 0.5 and 0.2 cm, respectively. The efficiency to reconstruct and identify muons is greater than 96%.…”