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Results from a search for neutrinoless double-beta decay (0νββ) of ^{136}Xe are presented using the first year of data taken with the upgraded EXO-200 detector. Relative to previous searches by EXO-200, the energy resolution of the detector has been improved to σ/E=1.23%, the electric field in the drift region has been raised by 50%, and a system to suppress radon in the volume between the cryostat and lead shielding has been implemented. In addition, analysis techniques that improve topological discrimination between 0νββ and background events have been developed. Incorporating these hardware and analysis improvements, the median 90% confidence level 0νββ half-life sensitivity after combining with the full data set acquired before the upgrade has increased twofold to 3.7×10^{25}  yr. No statistically significant evidence for 0νββ is observed, leading to a lower limit on the 0νββ half-life of 1.8×10^{25}  yr at the 90% confidence level.

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A search for neutrinoless double-β decay (0νββ) in 136 Xe is performed with the full EXO-200 dataset using a deep neural network to discriminate between 0νββ and background events. Relative to previous Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP 3 .

We show that a distribution of micrometer-sized calcifications in the human breast which are not visible in clinical x-ray mammography at diagnostic dose levels can produce a significant dark-field signal in a grating-based x-ray phase-contrast imaging setup with a tungsten anode x-ray tube operated at 40 kVp. A breast specimen with invasive ductal carcinoma was investigated immediately after surgery by Talbot-Lau x-ray interferometry with a design energy of 25 keV. The sample contained two tumors which were visible in ultrasound and contrast-agent enhanced MRI but invisible in clinical x-ray mammography, in specimen radiography and in the attenuation images obtained with the Talbot-Lau interferometer. One of the tumors produced significant dark-field contrast with an exposure of 0.85 mGy air-kerma. Staining of histological slices revealed sparsely distributed grains of calcium phosphate with sizes varying between 1 and 40 μm in the region of this tumor. By combining the histological investigations with an x-ray wave-field simulation we demonstrate that a corresponding distribution of grains of calcium phosphate in the form of hydroxylapatite has the ability to produce a dark-field signal which would-to a substantial degree-explain the measured dark-field image. Thus we have found the appearance of new information (compared to attenuation and differential phase images) in the dark-field image. The second tumor in the same sample did not contain a significant fraction of these very fine calcification grains and was invisible in the dark-field image. We conclude that some tumors which are invisible in x-ray absorption mammography might be detected in the x-ray dark-field image at tolerable dose levels.

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...

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