Physics Performance of the Barrel RPC System of the HARP Experiment

The physics performance of the barrel RPC system of the HARP experiment is described. In the barrel two sets of fifteen identical resistive plate chambers (RPCs) have been operated in 2001 and 2002 as a part of the HARP experiment at the CERN PS accelerator. For the first time under real experimental conditions RPCs have bean applied for particle identification (PID) by measuring the particle's time-of-flight (ToF). The procedure developed for the RPC calibration, based on reconstructed tracks in the HARP Time Projection Chamber (TPC), is described in detail. Intrinsic RPC time resolutions of 141 ps and a combined time resolution of the large angle TOF system of 180 ps are obtained. The effective resolution of the comparison of predicted and measured ToF is 305 ps in the region of interest for this experiment. The PID capabilities of the system are demonstrated. An average efficiency of the RPC counters of about 97% is measured

I. Introduction

The harp experiment [1], [2] has been designed to measure hadron production cross-sections on fixed targets with a precision of a few percent over almost the full solid angle. A set of solid and liquid targets spanning a large range in atomic number was exposed to beams of protons and pions with momenta between 1.5 GeV/c and 15 GeV/c. The elements used ranged from hydrogen to lead. HARP took 450 million physics triggers, collected data for about 300 different settings and recorded 30 TB of information from August 2001 to October 2002.