A study to suppress a sneaking cosmic muon background in the COMET experiment

TL;DR

This paper presents a method to significantly reduce cosmic muon background in the COMET experiment by using track-fitting quality to discriminate muon directions, enhancing the experiment's sensitivity.

Contribution

The study introduces a novel track-fitting quality technique to suppress sneaking cosmic muons, improving background rejection in muon-to-electron conversion searches.

Findings

Background reduced by an order of magnitude.

Method validated through Monte Carlo simulations.

Enhanced sensitivity for muon-to-electron conversion detection.

Abstract

The COMET experiment, conducted at J-PARC, aims to search for muon-to-electron conversion with an unprecedentedly high sensitivity. One of the severest backgrounds in the Phase-I experiment originates from cosmic-ray muons. A cosmic muon sneaks into a detector solenoid magnet from a loophole, scattered and leaving a track in a cylindrical drift chamber. Among them, a positive muon track with reverse direction may mimic a signal electron of 105 MeV/$c$. In order to suppress the sneaking cosmic positive muon background, we developed a method to discriminate the track direction by using track-fitting quality. We demonstrated that the positive muon background can be reduced by an order of magnitude. In this paper, we will report the methodology, a Monte Carlo simulation and results with prospects.