Reflectivity of VUV-sensitive Silicon Photomultipliers in Liquid Xenon

Abstract

Silicon photomultipliers are regarded as a very promising technology for next-generation, cutting-edge detectors for low-background experiments in particle physics. This work presents systematic reflectivity studies of Silicon Photomultipliers (SiPM) and other samples in liquid xenon at vacuum ultraviolet (VUV) wavelengths. A dedicated setup at the University of Münster has been used that allows to acquire angle-resolved reflection measurements of various samples immersed in liquid xenon with 0.45 • angular resolution. Four samples are investigated in this work: one Hamamatsu VUV4 SiPM, one FBK VUV-HD SiPM, one FBK wafer sample and one Large-Area Avalanche Photodiode (LA-APD) from EXO-200. The reflectivity is determined to be 25-36 % at an angle of incidence of 20 • for the four samples and increases to up to 65 % at 70 • for the LA-APD and the FBK samples. The Hamamatsu VUV4 SiPM shows a decline with increasing angle of incidence. The reflectivity results will be incorporated in upcoming light response simulations of the nEXO detector.

Kiloton-scale xenon detectors for neutrinoless double beta decay and other new physics searches

“…Since the Rayleigh scattering length ≈ 30 − 50 cm is much smaller than the linear dimensions of the detector, the light propagation is diffusive and photons transit a substantially larger lin-ear distance than the detector size during propagation. Nonetheless, these simulations indicate that an absorption length of 80 m ( 40 m) for designs 1 (2) is sufficient to reach the desired total > 10% collection efficiency when combined with measured SiPM photon detection efficiencies [125,126] and reflectivities [129][130][131]. These absorption lengths are comparable to the lower limits extrapolated from existing measurements [111,132,133], and are expected to improve with Xe purity.…”

“…IV A 1), this goal should be achievable. However, if required, 136 Xe(n, γ) 137 Xe production can also be highly suppressed through the admixture of ∼10% by volume of 131 Xe (or, possibly, other noble elements with high neutron capture cross sections [116]). Since the thermal n capture cross section is roughly 2 orders-of-magnitude higher for 131 Xe relative to 136 Xe, the resulting number of captures on 136 Xe can be correspondingly decreased.…”

“…However, if required, 136 Xe(n, γ) 137 Xe production can also be highly suppressed through the admixture of ∼10% by volume of 131 Xe (or, possibly, other noble elements with high neutron capture cross sections [116]). Since the thermal n capture cross section is roughly 2 orders-of-magnitude higher for 131 Xe relative to 136 Xe, the resulting number of captures on 136 Xe can be correspondingly decreased. For an enriched detector, light isotopes such as 131 Xe would be depleted from the enr Xe during enrichment, but could be separated from the enrichment tails and added back at 10% concentration to sufficiently suppress any backgrounds.…”

“…Since the thermal n capture cross section is roughly 2 orders-of-magnitude higher for 131 Xe relative to 136 Xe, the resulting number of captures on 136 Xe can be correspondingly decreased. For an enriched detector, light isotopes such as 131 Xe would be depleted from the enr Xe during enrichment, but could be separated from the enrichment tails and added back at 10% concentration to sufficiently suppress any backgrounds.…”

Kiloton-scale xenon detectors for neutrinoless double beta decay and other new physics searches

“…Since the Rayleigh scattering length ≈ 30 − 50 cm is much smaller than the linear dimensions of the detector, the light propagation is diffusive and photons transit a substantially larger linear distance than the detector size during propagation. Nonetheless, these simulations indicate that an absorption length of 80 m ( 40 m) for designs 1 (2) is sufficient to reach the desired total > 10% collection efficiency when combined with measured SiPM photon detection efficiencies [121,122] and reflectivities [125][126][127]. These absorption lengths are comparable to the lower limits extrapolated from existing measurements [107,128,129], and are expected to improve with Xe purity.…”