Operation of silicon photomultipliers in a dilution refrigerator down to 9.4 mK towards a cryogenic cosmic ray muon veto system

TL;DR

This work demonstrates that FBK NUV-HD-cryo silicon photomultipliers can operate in a dilution refrigerator down to $T_{MC}=9.4\pm0.2$ mK, enabling a cryogenic cosmic-ray muon veto within ultra-low background experiments. The study provides a comprehensive characterisation of the SiPM’s single-photon response, gain, dark count rate, direct crosstalk, and correlated delayed avalanches as a function of overvoltage, revealing a breakdown voltage that decreases with temperature to $V_{bd,MC}=27.16\pm0.05$ V and gains in the $6\times10^{5}$–$9\times10^{5}$ electron range. It also highlights a notable increase in afterpulsing and long-lasting afterpulsing trains at mK temperatures, which can affect photon counting but may be mitigated with shorter integration windows or lower $\Delta V$. Finally, the paper presents initial proof-of-concept measurements of directly coupling a SiPM to a scintillator at mK temperatures, demonstrating detectable scintillation signals consistent with environmental gamma-rays and cosmic-ray muons, reinforcing the potential of a cryogenic muon veto for the QUEST-DMC program.

Abstract

We report the characterisation of a FBK NUV-HD-cryo silicon photomultiplier (SiPM) sensor operated in an 9.4 $\pm$ 0.2 mK environment inside a dilution refrigerator, towards the development of a cryogenic cosmic ray muon veto system to be operated internal to a dilution refrigerator required for low background experiments such as the QUEST-DMC dark matter search experiment. We characterise the single photon response and the gain (the charge produced per detected photon), the dark count noise rate, and correlated noise contributions as a function of operating voltage. This paper also reports first proof of concept measurements of using a SiPM directly coupled to scintillator in a 9.4 mK temperature environment, towards detecting candidate cosmic ray muon signals.

Figures (14)

• Figure 1: Simplified schematic diagram of the experimental setup used for the operation of a single NUV-HD-cryo SiPM in a cryogen-free dilution refrigerator.
• Figure 2: Left: Picture of the single NUV-HD-cryo SiPM tested in this work, mounted onto a PCB and housed inside a 7 cm (L) x 3.8 cm (W) x 1.4 cm copper box. An LED that emits in the red wavelength range is glued to the outside of the copper box, over a 1 mm clearance hole allowing direct line of sight to the SiPM for acquiring I-V curves in dark conditions. Right: Picture of the copper box (shown in left figure) mounted inside the dilution refrigerator. The copper box is attached to a copper stand thermally coupled to the mixing chamber plate, which reaches a base temperature of 9.4 $\pm$ 0.2 mK.
• Figure 3: Left: Measured reverse I-V curve of the SiPM at $T_{\mathrm{MC}}$ (magenta) and room temperature (green), with breakdown voltages $V_{\mathrm{bd,MC}}$ = 27.16 $\pm$ 0.05 V ($V_{\mathrm{bd,RT}}$ = 32.18 $\pm$ 0.07 V) indicated by dashed red (green) lines. Right: Derivative of the reverse I-V curve, $\mathrm{dI/dV}$, as a function of $V_{\mathrm{bias}}$, acquired at $T_{\mathrm{MC}}$. $V_{\mathrm{bd}}$ is defined as the voltage at which $\mathrm{dI/dV}$ crosses a threshold of $\mu + 3\sigma$, indicated by the blue dashed line.
• Figure 4: Example waveform acquired at $V_{\mathrm{bias}}$ = 32 V ($\Delta V$ = 4.8 V), corresponding to a single dark count rate signal (equivalent to the single photon signal). Raw waveform (blue), baseline-subtracted and filtered waveform (orange), pulse finding threshold (red), and identified pulse time (green) are shown.
• Figure 5: Pulse amplitude (left) and pulse prompt charge (right) distributions of the NUV-HD-cryo SiPM operated at $V_{\mathrm{bias}}$ = 32 V ($\Delta V$ = 4.8 V). Gaussian functions are fit to the first 3 peaks in each histogram in order to extract the gain measured in amplitude (left) and charge (right). The first peak in each histogram corresponds to the 1 PE peak.