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...

We report on the performance of silicon photomultiplier (SiPM) light sensors operating in electric field strength up to 30 kV/cm and at a temperature of 149 K, relative to their performance in the absence of an external electric field. The SiPM devices used in this study show stable gain, photon detection efficiency, and rates of correlated pulses, when exposed to external fields, within the estimated uncertainties. No visible damage to the surface of the devices was caused by the exposure.

The vapor pressure isotopic effect (VPIE) of xenon has been measured using cryogenic distillation. The still is calibrated with argon and krypton and yields a measurement of ln­(p 130/p 136) ≃ (0.26 ± 0.04) × 10–3, where p 130 and p 136 are the vapor pressures of 130Xe and 136Xe at the nominal boiling point, respectively. The dependence of the VPIE across the isotopes for the three elements is found to be approximately linear with atomic mass, and all values are consistent with theoretical expectations.

The goal of this research was to study the xenon vapour pressure isotope effect (VPIE) and this was done to explore the feasibility of doing the Xe enrichment, using a 1.83 m high, cryogenic distillation column at Carleton University. One of the famous isotopes for the 0vββ decay detection is 136 Xe which is not easily available in pure form, and it is available from the Centrifuge systems in Russia. Therefore, the VPIE of xenon isotopes were needed which have not been measured to date. The VPIE from this work would be 5.28 x 10-5 while the theoretical value reported by Tew is 5.17 x10-5 per mass unit. Thus, the experimental and theoretical values agree with the accuracy of the present slope measurement. Moreover, the data demonstrate for the first time the linear dependence of the VPIE across a range of isotopes, and this is consistent with the theoretical predictions.

A central topic in the development of understanding of the nature of neutrinos is the search for neutrino-less double beta decay. As increasingly sensitive detectors are required for such searches, a major cost and feasibility concern is the availability of sufficient separated isotope for the chosen target. 136Xe is a very attractive target for these studies. At present this isotope is only available from the Centrifuge systems in Russia. We are exploring the feasibility of doing this enrichment using distillation. To start this study we require the vapour pressure differences of the xenon isotopes which have not been measured to date. This paper will describe the measurement of these vapour pressures using a tall cryogenic distillation process.