C. Carrillo

The upgrade of the CMS RPC system during the first LHC long shutdown

The CMS muon system includes in both the barrel and endcap region Resistive Plate Chambers (RPC). They mainly serve as trigger detectors and also improve the reconstruction of muon parameters. Over the years, the instantaneous luminosity of the Large Hadron Collider gradually increases. During the LHC Phase 1 ( ~ first 10 years of operation) an ultimate luminosity is expected above its design value of 1034 cm−2s−1 at 14 TeV. To prepare the machine and also the experiments for this, two long shutdown periods are scheduled for 2013-2014 and 2018-2019. The CMS Collaboration is planning several detector upgrades during these long shutdowns. In particular, the muon detection system should be able to maintain a low-pT threshold for an efficient Level-1 Muon Trigger at high particle rates. One of the measures to ensure this, is to extend the present RPC system with the addition of a 4th layer in both endcap regions. During the first long shutdown, these two new stations will be equipped in the region |η| < 1.6 with 144 High Pressure Laminate (HPL) double-layer RPCs operating in avalanche mode, with a similar design as the existing CMS endcap chambers. Here, we present the upgrade plans for the CMS RPC system for the fist long shutdown, including trigger simulation studies for the extended system, and details on the new HPL production, the chamber assembly and the quality control procedures.

Uniformity and Stability of the CMS RPC Detector at the LHC

The Resistive Plate Chambers (RPCs) are employed in the CMS experiment at the LHC as dedicated trigger system both in the barrel and in the endcap. This note presents results of the RPC detector uniformity and stability during the 2011 data taking period, and preliminary results obtained with 2012 data. The detector uniformity has been ensured with a dedicated High Voltage scan with LHC collisions, in order to determine the optimal operating working voltage of each individual RPC chamber installed in CMS. Emphasis is given on the procedures and results of the High Voltage calibration. Moreover, an increased detector stability has been obtained by automatically taking into account temperature and atmospheric pressure variations in the CMS cavern.

Tests of multigap RPCs for high-η triggers in CMS

In this paper, we report a systematic study of multigap Resistive Plate Chambers (RPCs) for high-η triggers in CMS. Prototype RPC modules with four- and six-gap structures have been constructed with phenolic high-pressure-laminated (HPL) plates and tested with cosmic muons and gamma rays irradiated from a 200-mCi 137Cs source. The detector characteristics of the prototype multigap RPCs were compared with those of the double-gap RPCs currently used in the CMS experiment at LHC. The mean values for detector charges of cosmic-muon signals drawn in the four- and six-gap RPCs for the efficiency values in the middle of the plateau were about 1.5 and 0.9 pC, respectively, when digitized with charge thresholds of 150 and 100 fC, respectively. They were respectively about one third and one fifth of that drawn in the current CMS double-gap RPC with a charge threshold of 200 fC. We concluded from the current R&D that use of the current phenolic-HPL multigap RPCs is advantageous to the high-η triggers in CMS in virtue of the smaller detector pulses.

THE CMS RPC SYSTEM OVERVIEW

The Muon System of the CMS experiment at CERN employees three different detector technologies—Drift Tube Chambers (DT) in the barrel part, Cathode Strip Chambers (CSC) in the endcaps and Resistive Plate Chambers (RPC) both in the barrel and the endcaps. TDs and CSCs serve as precise muon trajectory measurement devices. The RPCs are responsible for the bunch crossing identification and for a fast muon transverse momentum measurement. The total number of RPCs is 480 in the barrel and 756 in the endcaps, covering an area of about 3500 square meters. A brief overview of the system will be presented as well as some recent results about the system stability and performance.

Simulation of the CMS Resistive Plate Chambers

The Resistive Plate Chamber (RPC) muon subsystem contributes significantly to the formation of the trigger decision and reconstruction of the muon trajectory parameters. Simulation of the RPC response is a crucial part of the entire CMS Monte Carlo software and directly influences the final physical results. An algorithm based on the parametrization of RPC efficiency, noise, cluster size and timing for every strip has been developed. Experimental data obtained from cosmic and proton-proton collisions at ?s = 7 TeV have been used for determination of the parameters. A dedicated validation procedure has been developed. A good agreement between the simulated and experimental data has been achieved.