The time response of glass Resistive Plate Chambers to heavily ionizing particles

Abstract

The HARP system of resistive plate chambers (RPCs) was designed to perform particle identification by the measurement of the difference in the time-of-flight of different particles. In previous papers an apparent discrepancy was shown between the response of the RPCs to minimum ionizing pions and heavily ionizing protons. Using the kinematics of elastic scattering off a hydrogen target a controlled beam of low momentum recoil protons was directed onto the RPC chambers. With this method the trajectory and momentum, and hence the time-of-flight of the protons can be precisely predicted without need for a measurement of momentum of the protons. It is demonstrated that the measurement of the time-of-arrival of particles by the thin gas-gap glass RPC system of the HARP experiment depends on the primary ionization deposited by the particle in the detector.-1 -

Cross-sections of large-angle hadron production in proton- and pion-nucleus interactions I: beryllium nuclei and beam momenta of +8.9 GeV/c and −8.0 GeV/c

“…As discussed in Refs. [3] and [4], and succinctly summarized in this paper's Appendix, our calibrations disagree with calibrations published by the 'HARP Collaboration' [5][6][7][8]. Conclusions of independent review bodies on the discrepancies between our results and those from the HARP Collaboration can be found in Refs.…”

“…The p T resolution of tracks can be significantly improved by the use of the beam point 7) as an additional point to the trajectory in the TPC. The transverse coordinates of the beam point are known from the extrapolation of the trajectory of the incoming beam particle.…”

Comments on TPC and RPC calibrations reported by the HARP collaboration

“…Figure 5 shows that HARP's time advance of protons (black points; data from ref. [2]) is satisfactorily explained by a simulation of the time advance that results from a bias…”

“…This ion cloud emanates from the TPC's sense wires and drifts across its active volume toward the high-voltage membrane. 2 These dynamic track distortions increase approximately linearly with time in the spill. Their size in the r·φ coordinate typically reaches 15 mm, at small radius, at the end of the spill.…”

Latest results from HARP

“…Calibrations and corrections for the TPC and RPCs are now complete. Benchmarking of momentum reconstruction and track efficiency has been provided by the study of elastic scatting in the liquid H 2 target, in which the large angle particle is completely determined by the measurement of the angles of the forward low angle scatter [12][13] [14]. The measurement of pion yields in p--Ta interactions, in view of its importance for the neutrino factory [15] design, was the first large angle analysis produced [11].…”