Pion contamination in the MICE muon beam

TL;DR

This paper reports on the measurement of pion contamination in the MICE muon beam, demonstrating it meets the strict purity requirements essential for studying ionization cooling of muons.

Contribution

It provides the first upper limit measurement of pion contamination in the MICE muon beam, confirming contamination is below 1.4% at 90% confidence level.

Findings

Pion contamination in the MICE muon beam is less than 1.4% at 90% CL.

The beam's purity meets the requirements for ionization cooling experiments.

The particle-identification system effectively distinguishes muons from pions.

Abstract

The international Muon Ionization Cooling Experiment (MICE) will perform a systematic investigation of ionization cooling with muon beams of momentum between 140 and 240\,MeV/c at the Rutherford Appleton Laboratory ISIS facility. The measurement of ionization cooling in MICE relies on the selection of a pure sample of muons that traverse the experiment. To make this selection, the MICE Muon Beam is designed to deliver a beam of muons with less than $\sim$1\% contamination. To make the final muon selection, MICE employs a particle-identification (PID) system upstream and downstream of the cooling cell. The PID system includes time-of-flight hodoscopes, threshold-Cherenkov counters and calorimetry. The upper limit for the pion contamination measured in this paper is $f_\pi < 1.4\%$ at 90\% C.L., including systematic uncertainties. Therefore, the MICE Muon Beam is able to meet the stringent pion-contamination requirements of the study of ionization cooling.