Speaker
Description
The MEG II experiment at PSI searches for the charged lepton flavor violating decay, $\mu\to e\gamma$. The physics run commenced in 2021 and is planned to continue until the end of 2026, aiming at a target sensitivity on the branching ratio of $6\times 10^{−14}$. Based on data from 2021 and 2022, we have set the most stringent upper limit to date on the branching ratio at BR($\mu\to e\gamma$) < 1.5 × 10$^{-13}$ at a 90% confidence level.
Positron timing is measured by pixelated Timing Counter (pTC), a detector consisting of 512 plastic scintillator tiles, each with an intrinsic time resolution of 80 - 120 ps. By combining signals from multiple hits, the pTC achieves an excellent average time resolution of 43 ps.
While the pTC performance during the 2021-2022 run was robust, a bias in the measurement of time difference between photon and positron, dependent on the number of hit tiles in the pTC, was observed. This presentation will report on the calibration of the pTC using 2023-2024 dataset and detail the investigation into the origin of the hit-dependent timing bias found in the earlier data.
