Performance of novel VUV-sensitive Silicon Photo-Multipliers for nEXO

TL;DR

This paper evaluates the performance of new VUV-sensitive Silicon Photo-Multipliers for the nEXO experiment, aiming to improve detection efficiency and energy resolution in liquid xenon detectors for neutrinoless double beta decay searches.

Contribution

It provides the first characterization of the Fondazione Bruno Kessler VUVHD3 SiPMs and updates on Hamamatsu VUV4 MPPCs for nEXO, informing detector design improvements.

Findings

VUVHD3 SiPMs show promising photon detection efficiency at 163 K.

Measured parameters enable refined energy resolution estimates for nEXO.

Results support the feasibility of achieving sub-1% energy resolution.

Abstract

Liquid xenon time projection chambers are promising detectors to search for neutrinoless double beta decay (0$\nu \beta \beta$), due to their response uniformity, monolithic sensitive volume, scalability to large target masses, and suitability for extremely low background operations. The nEXO collaboration has designed a tonne-scale time projection chamber that aims to search for 0$\nu \beta \beta$ of \ce{^{136}Xe} with projected half-life sensitivity of $1.35\times 10^{28}$~yr. To reach this sensitivity, the design goal for nEXO is $\leq$1\% energy resolution at the decay $Q$-value ($2458.07\pm 0.31$~keV). Reaching this resolution requires the efficient collection of both the ionization and scintillation produced in the detector. The nEXO design employs Silicon Photo-Multipliers (SiPMs) to detect the vacuum ultra-violet, 175 nm scintillation light of liquid xenon. This paper reports on the characterization of the newest vacuum ultra-violet sensitive Fondazione Bruno Kessler VUVHD3 SiPMs specifically designed for nEXO, as well as new measurements on new test samples of previously characterised Hamamatsu VUV4 Multi Pixel Photon Counters (MPPCs). Various SiPM and MPPC parameters, such as dark noise, gain, direct crosstalk, correlated avalanches and photon detection efficiency were measured as a function of the applied over voltage and wavelength at liquid xenon temperature (163~K). The results from this study are used to provide updated estimates of the achievable energy resolution at the decay $Q$-value for the nEXO design.