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

The Muong−2experiment, E989, is currently taking data at Fermilab with the aim ofreducing the experimental error on the muon anomaly by a factor of four and possibly clarifyingthe current discrepancy with the theoretical prediction. A central component of this four-foldimprovement in precision is the laser calibration system of the calorimeters, which has to monitorthe gain variations of the photo-sensors with a 0.04% precision on the short-term (∼1ms). Thisis about one order of magnitude better than what has ever been achieved for the calibration of aparticle 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 reviewsthe design, the implementation and the performance of the Muong−2laser calibration system,showing how the experimental requirements have been met.