The Ring Imaging Cherenkov detector of the AMS experiment: test beam results with a prototype

TL;DR

This paper reports on test beam results of a prototype RICH detector for the AMS experiment, demonstrating its capability to measure cosmic particle velocity and charge with high precision, confirming the design goals.

Contribution

It presents the first performance evaluation of a RICH detector prototype for AMS using test beam data, including radiator and mirror characterization.

Findings

Confirmed velocity resolution of ~0.1% for singly charged particles.

Validated radiator materials and mirror reflectivity meet design specifications.

Demonstrated effective charge separation up to iron.

Abstract

The Alpha Magnetic Spectrometer (AMS) to be installed on the International Space Station (ISS) will be equipped with a proximity Ring Imaging Cherenkov (RICH) detector for measuring the velocity and electric charge of the charged cosmic particles. This detector will contribute to the high level of redundancy required for AMS as well as to the rejection of albedo particles. Charge separation up to iron and a velocity resolution of the order of 0.1% for singly charged particles are expected. A RICH protoptype consisting of a detection matrix with 96 photomultiplier units, a segment of a conical mirror and samples of the radiator materials was built and its performance was evaluated. Results from the last test beam performed with ion fragments resulting from the collision of a 158 GeV/c/nucleon primary beam of indium ions (CERN SPS) on a lead target are reported. The large amount of collected data allowed to test and characterize different aerogel samples and the sodium fluoride radiator. In addition, the reflectivity of the mirror was evaluated. The data analysis confirms the design goals.