Search

Several small single gap Resistive Plate Chambers and two RB1 CMS final stations have been exposed during the last year at the CERN Gamma Irradiation Facility to study possible long-term ageing effects. Up to now, an integrated charge of about 0.05 C / ( cm 2 gap ) and 0.025 C/(cm 2 gap) has been accumulated for the small RPCs and the large RB1 stations, respectively. Current, rate, fast charge and efficiency have been continuously monitored with muon beam or cosmics. Results concerning operation with a moisty mixture are also reported.

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.

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.

All the CMS muon stations will be equipped with Resistive Plate Chambers (RPCs). They will be exposed to high neutron background environment during the LHC running. In order to verify the safe operation of these detectors, an irradiation test has been carried out with two RPCs at high neutron flux (about ), integrating values of dose and fluence equivalent to 10 LHC-years. Before and after the irradiation, the performance of the detectors was studied with cosmic muons, showing no relevant aging effects. Moreover, no indication of damage or chemical changes were observed on the electrode surfaces.

In this paper, we describe a dedicated test to study possible long-term aging effects on Resistive Plate Chambers (RPCs). A double gap detector was operated under gamma irradiation for a period approximately equal to 10 years of LHC in the CMS-barrel region: an integrated dose of about and a total charge of about gap were accumulated on the chamber. The results show no relevant aging effect. Also the RPC sensitivity to gamma energies is measured.

The Resistive Plate Chambers [M. Abbrescia, et al., Nucl. Instr. and Meth. A 550 (2005) 116] are used in the CMS experiment [CMS Collaboration, The CMS experiment at the CERN LHC 2008, J. Inst. 3 (2008) S08004] as a dedicated muon trigger both in barrel and endcap system. About 4000m2 of double gap RPCs have been produced and have been installed in the experiment since more than one and half Years. The full barrel system and a fraction of the endcaps have been monitored to study dark current behaviour and system stability, and have been extensively commissioned with Cosmic Rays collected by the full CMS experiment.

A full-size prototype of the second barrel RPC station (RB2) for the CMS detector has been tested under high-irradiation flux at the CERN Gamma Irradiation Facility (GIF) during the 1999 beam test. The main requirements of RPCs as trigger detector have been studied: cluster size, time resolution, efficiency and rate capability. The timing features of a new front-end electronics were also investigated. Only the results obtained with the detector working in single-gap mode are reported here.

Two large double-gap resistive plate chambers, with 2 and 3 mm gap widths, were tested to study their response uniformity when operated in avalanche mode. The effects of mechanical tolerances and the presence of the spacers is thoroughly examined. Results on efficiency and time resolution are presented. We find that average performance and response uniformity over the whole chamber surface are fully adequate to the requirements of future collider experiments.

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.

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.

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.

The performance at low pressure of 2 mm gap bakelite Resistive Plate Chambers, operated in streamer mode with a gas mixture of 58% Ar, 40% n-butane and 2% CF3Br, have been studied. Efficiency, time resolution and strip multiplicity appear satisfactory up to pressures of about 600 mbar, corresponding to altitudes around 4000m a.s.l.

A 2 mm gas gap Resistive Plate Chamber with bakelite plates has been operated in avalanche mode with a 137 Cs source. We report measurements of the efficiency for a cosmic ray detection and the charge developed in the gap, performed for two different gas mixtures: the first containing a high percentage of environmental friendly “freon” C 2 H 2 F 4 ; the second one having a high percentage of argon. We show that the freon-based mixture exhibits a wide full-efficiency plateau with low streamer probability, while the argon-based mixture allows a reduction in the detector power consumption.

The performance of the Resistive Plate Chambers-based muon trigger of the CMS detector has been studied by means of a full simulation of the system under realistic operating conditions. Requirements on the performance of the chambers are deduced.

The Resistive Plate Chambers (RPCs) sensitivity to neutrons has been simulated using GEANT code with MICAP and FLUKA interfaces. The calculations have been performed as a function of the neutrons energy in the range 0.02 eV–1 GeV. To evaluate the response of the detector in the LHC background environment, the neutron energy spectrum expected in the CMS muon barrel has been taken into account; a hit rate due to neutrons of about 0.6 Hz cm−2 has been estimated for a RPC in the RB1 station

A general purpose shower parametrization algorithm for sampling calorimeters, which reproduces realistic fluctuations of the signal, is described. It makes use of multivariate statistical analysis to infer a limited number of significant factors from the data correlation matrix. Showers can be generated on the basis of those factors via a simple analytical model. Limited data samples from experiment or Monte Carlo may be equivalently used as input, allowing either the generation of experimental-like showers or the production with a negligible computer time of a large Monte Carlo-like sample.

The strip readout system of the Aleph streamer tubes hadron calorimeter is described. The system is based on a Fastbus module named ASTROS (Aleph STrip ReadOut Scanner) which performs data reduction and formatting.

The response to pions of an ALEPH electromagnetic calorimeter petal combined with the ALEPH hadron calorimeter prototype has been studied in the energy range between 2 and 30 GeV. The resolution of the combined calorimeters was found to be lower than that for the hadron calorimeter alone at low energies and approached this value at higher energies.