The upgrade of endcap CMS muon system
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e Upgrade of Endcap CMS Muon System V. Yu. Karjavin* (for CMS collaboration) Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia *e-mail: [email protected] Abstract⎯The configuration and composition of the CMS muon system are presented. The paper is focused on cathode strip chambers (CSC) used as the endcap muon system detectors. The goals and objectives of the endcap muon system upgrade are formulated. The main results of works accomplished for the ME1/1 CSCs upgrade and the new ME4/2 muon station construction during the LHC Long Shutdown-1 (2013–2014) are presented. The improved performances of the endcap muon system are shown using experimental data obtained after the upgrade (Run2 data). DOI: 10.1134/S1063779618010197
INTRODUCTION Identification of muons in proton–proton interactions at the Large Hadron Collider (LHC) provides an opportunity to study a wide range of physical processes and is the primary goal of the muon system of the Compact Muon Solenoid (CMS) experimental setup. The CMS muon system consists of two independent units: barrel and endcap (Fig. 1). Each includes four layers of muon stations alternated with disks of return iron yoke of the magnet. The CMS muon system is based on detectors of three different production technologies: drift tubes (DT) mounted in the barrel part; resistive plate chambers (RPC) mounted in the barrel and endcap parts; and chambers reading information from cathode strips (CSC) located in the endcaps. This paper presents the goals and results of the upgrade of the CMS muon system endcap cathode strip chambers carried out during the LHC first longterm shutdown [1]. The cathode strip chambers register muons with high accuracy in the field of pseudorapidities 1.2 < |η| < 2.4; they operate in conditions of a nonhomogeneous magnetic field and high-level radiation background. The CMS endcap muon system is comprised of four muon stations (МЕ1/1-МЕ4), including 468 cathode strip chambers. Each chamber consists of seven laminated panels forming six gas gaps with anode wires stretched between two cathode planes. The voltage of 2.9–3.6 kV is applied to the anode wires. The track coordinates are determined by distribution of the charge induced onto strips and electronic signal from the anode wires. The information read from the cathode strips with width of 3–16 mm cut on the laminated panel surface determines the muon azimuthal coordinates, which are important for measuring its transverse momentum. Information obtained from the anode wires provides an opportunity to mea-
sure the muon radial coordinates and the exact time mark of registration of the muon local track by each of the six planes of the chamber. Three-dimensional segments produced by fitting the muon local coordinates at each of six planes of the chamber and termed charged tracks form the primitives for generating a trigger in the given area of interest. The ME1/1 forward muon station is the major detector of the forward endcap of the CMS setup [2]. The МЕ1/1 is located inside a solenoid of t
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