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

Abstract

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