Performance of the Muon g−2 calorimeter and readout systems measured with test beam data

Abstract

A single calorimeter station for the Muon g − 2 experiment at Fermilab includes the following subsystems: a 54-element array of PbF 2 Cherenkov crystals read out by large-area SiPMs, bias and slow-control electronics, a suite of 800 MSPS waveform digitizers, a clock and control distribution network, a gain calibration and monitoring system, and a GPU-based frontend read out through a MIDAS data acquisition environment. The entire system performance was evaluated using 2.5 − 5 GeV electrons at the End Station Test Beam at SLAC. This paper includes a description of the individual subsystems and the results of measurements of the energy response and resolution, energy-scale stability, timing resolution, and spatial uniformity. All measured performances meet or exceed the g − 2 experimental requirements. Based on the success of the tests, the complete production of the required 24 calorimeter stations has been made and installation into the main experiment is complete. Furthermore, the calorimeter response measurements determined here informed the design of the reconstruction algorithms that are now employed in the running g − 2 experiment. to determine the anomalous magnetic moment a µ ≡ (g − 2)/2 of the muon to a relative precision of 140 parts per billion (ppb). The measurement is made by observing the spin precession frequency ω s relative to the cyclotron frequency ω c for muons orbiting a highly uniform magnetic storage ring with

Measurement of the anomalous precession frequency of the muon in the Fermilab Muon g-2 experiment

“…Each calorimeter station, described in detail elsewhere [35][36][37], consists of a 9 column by 6 row array of PbF 2 crystals instrumented with silicon photomultiplier (SiPM) photodetectors. Digitization of the output from each of the 24 × 54 channels occurs continuously over an entire fill at a rate of approximately 800 Megasamples per second (MSPS).…”

“…The local approach fits pulses with an amplitude over a configurable threshold in each crystal independently. References [36,42] describe the template pulse fitting algorithm utilized in this step in detail. Should two or more pulses occur within the length of the pulse template (250 ns), the algorithm refits them simultaneously, using the results of the initial fits as starting parameters, to remove effects due to the tail of the first pulse overlapping with the second one.…”

“…After applying a time correction to each crystal similar to that described in Sec. IV A, the clusters identified in the time window are fit by minimizing a χ 2 described in Section VI D. Because the SiPM pulse shape for a crystal does not depend on the pulse magnitude [36], we can model each trace by a crystal-dependent template that scales with energy and translates with time. The pulse magnitude for each crystal pulse floats independently in the fit.…”

Magnetic Field Measurement and Analysis for the Muon g-2 Experiment at Fermilab

“…The experiment was designed to balance the statistical and systematic uncertainties to reach its precision goal. The measurement of ω a [2] is based on the time dependence of the decay positrons above an energy threshold measured in 24 electromagnetic calorimeters [28][29][30] with gain stabilized by a laser system [31]. Two in-vacuum straw trackers [32] provide the detailed information about the distribution of the muons in the storage ring that determines how the magnetic field is weighted and inform the beam-dynamics corrections to a µ [3].…”

Beam dynamics corrections to the Run-1 measurement of the muon anomalous magnetic moment at Fermilab

“…ular aluminum window before striking a detector. Each calorimeter station consists of 54 lead-fluoride Cherenkov crystals read out individually on the downstream side by large-area silicon photomultipliers (SiPMs) [20,21]. The signals are continuously digitized at 800 megasamples per second.…”