The Search for $\mu^+\to e^+ \gamma$ with 10$^{-14}$ Sensitivity: the Upgrade of the MEG Experiment

TL;DR

The paper discusses the upgrade of the MEG experiment to improve sensitivity in detecting the rare muon decay ${ m oldsymbol{ extmu}^+ ightarrow ext{f e}^+ oldsymbol{ extgamma}}$, aiming for a sensitivity of 6×10⁻¹⁴, enhancing the search for lepton flavor violation.

Contribution

This work presents the design, implementation, and commissioning status of the upgraded MEG II detector to achieve higher sensitivity in lepton flavor violation searches.

Findings

Successful upgrade of detector components for higher rate capability.

Improved resolutions in measurements while maintaining detector concept.

Preparation and commissioning of MEG II for future data collection.

Abstract

The MEG experiment took data at the Paul Scherrer Institute in the years 2009--2013 to test the violation of the lepton flavour conservation law, which originates from an accidental symmetry that the Standard Model of elementary particle physics has, and published the most stringent limit on the charged lepton flavour violating decay ${\mu}^+ \rightarrow {\rm e}^+ \gamma$: BR(${\mu}^+ \rightarrow {\rm e}^+ \gamma$) $<4.2 \times 10^{-13}$ at 90% confidence level. The MEG detector has been upgraded in order to reach a sensitivity of $6\times10^{-14}$. The basic principle of MEG II is to achieve the highest possible sensitivity using the full muon beam intensity at the Paul Scherrer Institute ($7\times10^{7}$ muons/s) with an upgraded detector. The main improvements are better rate capability of all sub-detectors and improved resolutions while keeping the same detector concept. In this paper, we present the current status of the preparation, integration and commissioning of the MEG II detector in the recent engineering runs.