# The laser-based time calibration system for the MEG II pixelated Timing Counter

## TL;DR

This paper introduces a novel laser-based calibration system for the MEG II pixelated Timing Counter, achieving high precision timing alignment for highly segmented scintillator detectors using SiPMs.

## Contribution

A new laser calibration method tailored for highly segmented scintillator counters with SiPMs, overcoming limitations of previous methods for large-scale detectors.

## Key findings

- System demonstrated stability and sensitivity to ~10 ps timing changes.
- Achieved 48 ps uncertainty in time offset determination.
- Successfully implemented and tested in real experimental conditions.

## Abstract

We have developed a new laser-based time calibration system for highly segmented scintillator counters like the MEG II pixelated Timing Counter (pTC), consisting of 512-centimeter scale scintillator counters read out by silicon photomultipliers (SiPMs). It is difficult to apply previous laser-based calibration methods for conventional meter-scale Time-Of-Flight detectors to the MEG II pTC from the implementation and the accuracy points of view. This paper presents a new laser-based time calibration system which can overcome such difficulties. A laser pulse is split into each scintillator counter via several optical components so that we can directly measure the time offset of each counter relative to the laser-emitted time. We carefully tested all the components and procedures prior to the actual operation. The laser system was installed into the pTC and thoroughly tested under the real experimental condition. The system showed good stability and being sensitive to any change of timing larger than ~10 ps. Moreover, it showed an uncertainty of 48 ps in the determination of the time offsets, which meets our requirements. The new method provides an example of the implementation of a precise timing alignment for the new type of detectors enabled by the advance of SiPM technology.