VUV-Sensitive Silicon Photomultipliers for Xenon Scintillation Light Detection in nEXO

Abstract

Future tonne-scale liquefied noble gas detectors depend on efficient light detection in the VUV range. In the past years Silicon Photomultipliers (SiPMs) have emerged as a valid alternative to standard photomultiplier tubes or large area avalanche photodiodes. The next generation double beta decay experiment, nEXO, with a 5 tonne liquid xenon time projection chamber, will use SiPMs for detecting the 175 nm xenon scintillation light, in order to achieve an energy resolution of σ/Qββ = 1 %. This paper presents recent measurements of the VUV-HD generation SiPMs from Fondazione Bruno Kessler in two complementary setups. It includes measurements of the photon detection efficiency with gaseous xenon scintillation light in a vacuum setup and dark measurements in a dry nitrogen gas setup. We report improved photon detection efficiency at 175 nm compared to previous generation devices, that would meet the criteria of nEXO. Furthermore, we present the projected nEXO detector light collection and energy resolution that could be achieved by using these SiPMs. Index Terms-silicon photomultiplier, xenon detectors, photo detectors, vacuum ultra-violet light, nEXO I. NEUTRINO-LESS DOUBLE BETA DECAY AND NEXO N eutrino-less double beta decay (0νββ) is a hypothetical nuclear decay where two neutrons decay into two protons and two electrons are emitted but no anti-neutrinos are present in the final state. The observation of this process would have a fundamental impact on the Standard Model of Particle Physics, specifically showing a violation of lepton number conservation (|∆L| = 2), and would imply that the neutrino is a Majorana fermion [1], independently of the actual process enabling the decay [2]. Furthermore, the half-life of the decay would shed light on the absolute neutrino mass scale [3]. The nEXO collaboration plans to build a cylindrical singlephase time projection chamber (TPC) filled with 5 tonnes of liquid xenon (LXe), with 90 % enrichment in 136 Xe [4]. nEXO takes advantage of the experience from its predecessor EXO-200 [5], but will incorporate new light and charge detectors [6]. Together with cold electronics sitting inside the LXe, this allows nEXO to achieve an energy resolution of σ/Q ββ = 1 % for the 0νββ decay of 136 Xe (2458.07 ± 0.31 keV [7], [8]).In particular, instead of the EXO-200 Large Area Avalanche Photo-diodes (LAAPDs), nEXO will use Silicon Photomultipliers (SiPMs) for the detection of xenon scintillation light. The SiPMs will fully cover the lateral surface of the cylinder with a total photo-sensitive area of about 4 m 2 , as shown in Figure 1. The devices will be immersed in LXe and placed in the high field region behind the field shaping rings of the TPC field cage [9]. The performance of SiPMs has improved significantly over the past decade and they are especially interesting because of their high gain, on the order of 10 6 , and their single photon resolution capability.The half-life sensitivity of nEXO to the 0νββ decay of 136 Xe is projected to be 9.5 × 10 27 yr for 90 % C.L. after 10 years o...

Large-area MPPC with enhanced VUV sensitivity for liquid xenon scintillation detector

“…[12] that a MPPC based on the same technology showed a good performance in LAr to detect the scintillation light from LAr. Following our development, another vendor has also started to develop SiPMs with VUV sensitivities [13,14]. The VUV-MPPCs tested here were successfully installed in the MEG II LXe detector, which is now being commissioned.…”

Characterisation of a new generation of VUV low-light sensors

“…To meet nEXO requirements, the SiPM PDE must be ≥ 15% [7] for liquid xenon scintillation wavelengths (174.8 ± 10.2 nm [11]). In this paper, the PDE was measured using a filtered pulsed Hamamatsu L11035 xenon flash lamp enabling measurements free from correlated avalanches [2].…”

“…At this over voltage and temperature the electronics noise was measured to be 0.064 PE. [7], we assume a 10% error for the CE of this PMT (i.e. 71 ± 10%) to account for the non-uniformity of the photon collection efficiency at the photo-cathode.…”

“…Accordingly to recent simulations the first three constraints are in fact sufficient to achieve an energy resolution of 1% for the (0νββ) decay of 136 Xe [10]. In [7], it was shown that these requirements could be met with SiPMs developed by Fondazione Bruno Kessler (FBK, Trento, Italy). The aim of this paper is to assess the performance of Hamamatsu VUV4 Multi-Pixel Photon Counters (MPPC)s (S/N: S13370-6152) developed for application in liquid xenon as a possible alternative solution to FBK SiPMs.…”

“…Silicon PhotoMultipliers (SiPMs) are an emerging and very promising technology that address the challenge of sensing, timing and quantifying low-light signals down to the single-photon level [2][3][4][5]. For these reasons, large-scale low-background cryogenic experiments, such as the next-generation Enriched Xenon Observatory experiment (nEXO) [6], are migrating to a SiPM-based light detection system [7][8][9]. nEXO aims to probe the boundaries of the standard model of particle physics by searching for neutrino-less double beta decay (0νββ) of 136 Xe [10].…”