# COMET Phase-I Technical Design Report

## TL;DR

The COMET Phase-I experiment aims to detect neutrinoless muon-to-electron conversion with significantly improved sensitivity, utilizing advanced detectors and simulations to achieve low background levels at J-PARC.

## Contribution

This paper presents the detailed technical design of the COMET Phase-I experiment, including detector setup, sensitivity goals, and background estimation methods.

## Key findings

- Sensitivity goal of 3.1×10⁻¹⁵ for muon-electron conversion
- Expected background of 0.032 events
- Simulation results support feasibility of the experiment

## Abstract

The Technical Design for the COMET Phase-I experiment is presented in this paper. COMET is an experiment at J-PARC, Japan, which will search for neutrinoless conversion of muons into electrons in the field of an aluminium nucleus ($\mu-e$ conversion, $\mu^- N \to e^- N$); a lepton flavor violating process. The experimental sensitivity goal for this process in the Phase-I experiment is $3.1\times10^{-15}$, or 90 % upper limit of branching ratio of $7\times 10^{-15}$, which is a factor of 100 improvement over the existing limit. The expected number of background events is 0.032. To achieve the target sensitivity and background level, the 3.2 kW 8 GeV proton beam from J-PARC will be used. Two types of detectors, CyDet and StrECAL, will be used for detecting the \mue conversion events, and for measuring the beam-related background events in view of the Phase-II experiment, respectively. Results from simulation on signal and background estimations are also described.