Design and performance of SiPM-based readout of PbF₂ crystals for high-rate, precision timing applications

Abstract

We have developed a custom amplifier board coupled to a large-format 16-channel Hamamatsu silicon photomulplier device for use as the light sensor for the electromagnetic calorimeters in the Muon g − 2 experiment at Fermilab. The calorimeter absorber is an array of lead-fluoride crystals, which produces short-duration Cherenkov light. The detector sits in the high magnetic field of the muon storage ring. The SiPMs selected, and their accompanying custom electronics, must preserve the short pulse shape, have high quantum efficiency, be non-magnetic, exhibit gain stability under varying rate conditions, and cover a fairly large fraction of the crystal exit surface area. We describe an optimized design that employs the new-generation of thru-silicon via devices. The performance is documented in a series of bench and beam tests.

Measuring the Precession Frequency in the E989 Muon g – 2 Experiment

“…If the SiPM exhibited a rate dependent pulse shape, one would expect these two templates to differ. No significant difference was observed [63].…”

“…The overall hit rate in the absence of pileup is r(t), and the rate of pileup pulses is r 2 (t)∆t. [63]. Dashed lines show the traces that would have been recorded had either pulse arrived individually.…”

“…Gain is often defined as the charge collected per fired pixel divided by the elementary charge [68]. Figure 4.5: The E989 SiPM readout board, reproduced from [63]. A circuit schematic is available in the original article.…”

“…At this point, the APD acts like a capacitor and the current draw slowly decays as the capacitor charges back to the applied bias voltage, a process called pixel recovery. Avalanches themselves are very fast, yielding pulse rise times of approximately 3 ns[63,68]. Most of the measured current flows during the recovery process.…”

The New Muon g-2 Experiment at Fermilab: Commissioning and First Physics Data Taking

“…Sensitive to positrons between tens of MeV to a few GeV, their energy resolution of a few percent is more than adequate for the purpose of measuring the energy-dependent oscillating asymmetry in positron production which encodes the muon spin precession. The acceptance of the calorimeters to all decay positrons is roughly one-third due to the calorimeters' height (just over 15 cm) and the dipole field's tendency to bend decay positron trajectories inward [6] [7].…”