Temperature-Dependent Calibration Procedures for the Silicon Photomultiplier Readout of the Cosmic Ray Veto Detector for the Mu2e Experiment

TL;DR

This work addresses the challenge of calibrating SiPM based readouts for the Mu2e CRV when active cooling is not used. It presents a temperature dependent calibration framework derived from controlled chamber measurements, including a set of correction parameters that account for SiPM breakdown voltage, over voltage, FEB bias, and AFE gain effects. The method enables reconstruction of the light yield at a reference temperature and a robust, temperature independent efficiency for cosmic ray vetoing, with validation from both chamber data and CRV modules. The approach supports precise aging studies and can be applied to other SiPM based detectors requiring equalized response across temperatures.

Abstract

The cosmic ray veto detector for the Mu2e experiment consists of scintillation bars embedded with wavelength-shifting fibers and read out by silicon photomultipliers (SiPMs). In this manuscript the calibration procedures of the SiPMs are described including corrections for the temperature dependence of their light yield. These corrections are needed as the SiPMs are not kept at a constant temperature due to the complexity and cost of implementing a cooling system on such a large detector. Rather, it was decided to monitor the temperature to allow the appropriate corrections to be made. The SiPM temperature dependence has been measured in a dedicated experiment and the calibration procedures were validated with data from production detectors awaiting installation at Fermilab.

Figures (23)

• Figure 1: In the image, concrete blocks (red) surround the Mu2e beamline which you see entering on the right. The cosmic ray veto detector is mounted on the top and four sides of the blocks (grey) and surrounds the Mu2e detector.
• Figure 2: Exploded view of the manifold at the end of a di-counter showing the fiber guide bar, SiPM mounting block, SiPM carrier boards, SiPMs, and counter motherboard. The flasher LEDs, thermometer, and pogo pins are not shown.
• Figure 3: Architecture of the CRV readout for a "normal" module read out on both ends.
• Figure 4: A typical waveform and noise pulse appearing in a 127 ADC sample time slice, each sample separated by 12.5 ns. The pre-signal region shows a dark-count pulse of 1 PE at 400 ns. The signal region shows a signal pulse with 52 PEs. All pulses get fitted with a Gumbel function.
• Figure 5: The pedestal-subtracted dark count distribution of a single SiPM displays distinct peaks that correspond to one, two, and three photoelectrons. The location of the first peak (the single photoelectron peak, SPE) is utilized to extract the SPE calibration constant.