Dynamic Distortions in the HARP TPC: observations, measurements, modelling and corrections

TL;DR

This paper investigates the dynamic distortions in the HARP TPC caused by ion charge build-up, develops a correction method through modeling and experimental validation, and demonstrates improved data accuracy after correction.

Contribution

It introduces a comprehensive model and correction procedure for time-dependent distortions in the HARP TPC, validated through experimental benchmarks.

Findings

Corrected data matches distortion-free data performance.

Model accurately describes ion cloud dynamics and electrostatics.

Correction procedure effectively mitigates dynamic distortions.

Abstract

The HARP experiment was designed to study hadron production in proton- nucleus collisions in the energy range of 1.5 GeV/c-15 GeV/c. The experiment was made of two spectrometers, a forward dipole spectrometer and a large-angle solenoid spectrometer. In the large-angle spectrometer the main tracking and particle identification is performed by a cylindrical Time Projection Chamber (TPC) which suffered a number of shortcomings later addressed in the analysis. In this paper we discuss the effects of time-dependent (dynamic) distortions of the position measurements in the TPC which are due to a build-up of ion charges in the chamber during the accelerator spill. These phenomena have been studied both theoretically and experimentally, and a correction procedure has been developed. First, the dynamics of the positive ion cloud and of the full electrostatics of the field-cage system have been modelled with a phenomenological approach and a general correction procedure has been developed and applied to all data settings. Then, the correction procedure has been benchmarked experimentally by means of recoil protons in elastic scattering reactions, where the track coordinates are precisely predictable from simple kinematical considerations. After application of the corrections for dynamic distortions the corrected data have a performance equal to data where the dynamic distortions are absent. We describe the theoretical model, the comparison with the measurements, the distortion correction method and the results obtained with experimental data.