# The laser-based gain monitoring system of the calorimeters in the Muon $g-2$ experiment at Fermilab

## TL;DR

The paper describes the design, implementation, and performance of a highly precise laser calibration system for calorimeters in Fermilab's Muon g-2 experiment, crucial for reducing measurement errors and improving muon anomaly accuracy.

## Contribution

It introduces a novel laser calibration system achieving unprecedented short-term gain monitoring precision for particle physics calorimeters.

## Key findings

- Achieved 0.04% short-term gain monitoring precision
- Successfully monitored long-term gain variations below per mille level
- Met all experimental requirements for the Muon g-2 calorimeter calibration

## Abstract

The Muon $g-2$ experiment, E989, is currently taking data at Fermilab with the aim of reducing the experimental error on the muon anomaly by a factor of four and possibly clarifying the current discrepancy with the theoretical prediction. A central component of this four-fold improvement in precision is the laser calibration system of the calorimeters, which has to monitor the gain variations of the photo-sensors with a 0.04\% precision on the short-term ($\sim 1\,$ms). This is about one order of magnitude better than what has ever been achieved for the calibration of a particle physics calorimeter. The system is designed to monitor also long-term gain variations, mostly due to temperature effects, with a precision below the per mille level. This article reviews the design, the implementation and the performance of the Muon $g-2$ laser calibration system, showing how the experimental requirements have been met.