MEG II liquid xenon scintillation calorimeter to detect 52.8 MeV [formula omitted] with large area VUV-sensitive MPPCs

Abstract

The MEG II experiment will search for new physics like SUSY-GUT/SUSY-seesaw through the lepton flavor violating μ+→e+γ decay with ten times better sensitivity than the MEG experiment. The MEG experiment published the result of B(μ+→e+γ)<4.2×10−13 at 90% C.L. in 2016, which was thirty times better result than the previous limit. Because the sensitivity of the MEG experiment was already limited by accidental backgrounds, the MEG detector must be upgraded to reach one order of magnitude better sensitivity.The MEG experiment utilized 846 2 inch PMTs to detect scintillation light in a 900 L liquid xenon gamma calorimeter. On the γ incident face, 216 2 inch PMTs will be replaced with 4092 12 × 12 mm2 MPPCs to improve the energy and position resolution for γ events which interact near the incident face due to finer granularity and better uniformity of the scintillation light collection efficiency. We are now constructing the MEG II liquid xenon calorimeter. The detector calibration, purification, monitoring, and commissioning are in progress. Here the detector status will be described together with the expected detector performance.