P. Vitulo

A facility for the test of large-area muon chambers at high rates

Abstract Operation of large-area muon detectors at the future Large Hadron Collider (LHC) will be characterized by large sustained hit rates over the whole area, reaching the range of kHz cm −2 . We describe a dedicated test zone built at CERN to test the performance and the aging of the muon chambers currently under development. A radioactive source delivers photons causing the sustained rate of random hits, while a narrow beam of high-energy muons is used to directly calibrate the detector performance. A system of remotely controlled lead filters serves to vary the rate of photons over four orders of magnitude, to allow the study of performance as a function of rate.

The simulation of resistive plate chambers in avalanche mode: Charge spectra and efficiency

A model to simulate the avalanche formation process and the induced signal in a Resistive Plate Chamber is presented. A first investigation of the effects of various parameters on the performance of this detector is reported.

RESISTIVE PLATE CHAMBERS IN AVALANCHE MODE : A COMPARISON BETWEEN MODEL PREDICTIONS AND EXPERIMENTAL RESULTS

Abstract In this paper a model simulating the main aspects of avalanche growth and signal development in Resistive Plate Chambers (RPCs) is presented. The model has been used to compute the performances, in particular, charge distribution and efficiency of single- double- and multi-gap RPCs, and to compare them with the available experimental results. This model could be used to optimize the characteristics of this type of detector with a view to its use in the future large experiments at LHC: ATLAS and CMS.

Properties of C2H2F4-based gas mixture for avalanche mode operation of resistive plate chambers

Abstract Some properties of a 90% C 2 H 2 F 4 gas mixture, used to operate resistive plate chambers in the avalanche mode, are determined by comparing the experimental results with the prediction of simple analytical calculations. The fast charge distribution of the signal induced on pick-up electrodes is reproduced by means of a Monte Carlo simulation of the avalanche development. In addition, predictions for a gas mixture with poor content of C 2 H 2 F 4 are given for comparison.

Effect of the linseed oil surface treatment on the performance of resistive plate chambers

Abstract Results on the behaviour of several bakelite Resistive Plate Chambers (RPCs) without the linseed oil treatment of the internal electrodes will be presented. Efficiency, collected charge and cluster size distributions will be compared to the ones of a standard oiled RPC. Currents and single rate are the quantities most affected by the surface treatment of the electrodes beyond the optical/mechanical properties. A factor 4 less in currents and at least a factor 10 less in single rate is achieved using standard oiled RPCs operated in streamer mode.

Resistive plate chamber neutron and gamma sensitivity measurement with a 252Cf source

A bakelite double gap Resistive Plate Chamber (RPC), operating in avalanche mode, has been exposed to the radiation emitted from a 252Cf source to measure its neutron and gamma sensitivity. One of the two gaps underwent the traditional electrodes surface coating with linseed oil. RPC signals were triggered by fission events detected using BaF2 scintillators. A Monte Carlo code, inside the GEANT 3.21 framework with MICAP interface, has been used to identify the gamma and neutron contributions to the total number of collected RPC signals. A neutron sensitivity of (0.63±0.02)×10−3 (average energy 2 MeV) and a gamma sensitivity of (14.0±0.5)×10−3 (average energy 1.5 MeV) have been measured in double gap mode. Measurements done in single gap mode have shown that both neutron and gamma sensitivity are independent of the oiling treatment.

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.

An RPC-based Technical Trigger for the CMS Experiment

In the CMS experiment, sub-detectors may send special trigger signals, called “Technical Triggers”, for purposes like test and calibration. The Resistive Plate Chambers are part of the Muon Trigger System of the experiment, but might also produce a cosmic muon trigger to be used during the commissioning of the detectors, the CMS Magnet Test-Cosmic Challenge and the later running of CMS. The proposed implementation is based on the development of a new board, the RPC Balcony Collector (RBC); the test results on prototypes and their performance during the recent CMS Cosmic Challenge are presented.

First results on RB2 muon barrel RPC detector for CMS

The first CMS MB2 station, with one RPC and one DT module, has been tested with a muon beam under a high intensity photon flux at the CERN Gamma Irradiation Facility during the Autumn 2001 test. Results on efficiency, rate capability, cluster size and spatial resolution, for the RPC detector, are reported here. Studies with a small percentage of SF6 in the gas mixture, in order to decrease the noise rate, have also been carried out.

The RPC system for the CMS experiment at the LHC

The CMS detector at the LHC has a redundant muon system. Two independent muon systems are used in the L1 trigger. One of them is based on wire chambers, the other on RPC detectors. Properly combining the answers of the two systems results in a highly efficient L1 trigger with high flexibility from the point of view of rate control. Simulation results show, however, that the RPC system suffers from false triggers caused by coincidence of spurious hits. System improvements, which could avoid oiling the chambers, are possible. RPCs have also proved to be very useful for muon track reconstruction.