The Readout Controller for the Calibration System of the Muon g-2 Experiment

Abstract

The Muon g-2 experiment at Fermilab will measure the muon anomalous magnetic moment $a=(g-2)/2$ to an unprecedented precision of 0.14 parts per million (ppm). To this aim, a calibration system made by a laser source and light distribution will provide short light pulses directly into each crystal of the 24 calorimeters to measure energy and arrival time of the decay positrons. Each calorimeter is composed of a $6\times 9$ matrix of $PbF_{2}$ crystals where each crystal is read by a silicon photomultiplier. Continuous monitoring and state-of-the-art calibration are required in order to control the detector response. The calibration light pulses are monitored, both at the laser output (source monitor) and at the end of the distribution system (local monitor), before delivery to the calorimeters. For example, the light pulses are read by specific photodetectors, whose signals are digitized by electronics designed to match the experimental requirements. All readout electronics boards are hosted in a crate where the controller manages the complete data collection, operates as an event builder and transfers data to the online farm system through a gigabit Ethernet connection. This data acquisition (DAQ) system is designed around a custom protocol and hardware to achieve high data transfer rate and event-building capability without software overhead. In this paper, after a general outline of this DAQ system, we describe in detail the main features of controller.