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.
A search for neutrinoless double-β decay (0νββ) in Xe136 is performed with the full EXO-200 dataset using a deep neural network to discriminate between 0νββ and background events. Relative to ...previous analyses, the signal detection efficiency has been raised from 80.8% to 96.4±3.0%, and the energy resolution of the detector at the Q value of Xe136 0νββ has been improved from σ/E=1.23% to 1.15±0.02% with the upgraded detector. Accounting for the new data, the median 90% confidence level 0νββ half-life sensitivity for this analysis is 5.0×1025 yr with a total Xe136 exposure of 234.1 kg yr. No statistically significant evidence for 0νββ is observed, leading to a lower limit on the 0νββ half-life of 3.5×1025 yr at the 90% confidence level.
Many extensions of the standard model of particle physics suggest that neutrinos should be Majorana-type fermions-that is, that neutrinos are their own anti-particles-but this assumption is difficult ...to confirm. Observation of neutrinoless double-β decay (0νββ), a spontaneous transition that may occur in several candidate nuclei, would verify the Majorana nature of the neutrino and constrain the absolute scale of the neutrino mass spectrum. Recent searches carried out with (76)Ge (the GERDA experiment) and (136)Xe (the KamLAND-Zen and EXO (Enriched Xenon Observatory)-200 experiments) have established the lifetime of this decay to be longer than 10(25) years, corresponding to a limit on the neutrino mass of 0.2-0.4 electronvolts. Here we report new results from EXO-200 based on a large (136)Xe exposure that represents an almost fourfold increase from our earlier published data sets. We have improved the detector resolution and revised the data analysis. The half-life sensitivity we obtain is 1.9 × 10(25) years, an improvement by a factor of 2.7 on previous EXO-200 results. We find no statistically significant evidence for 0νββ decay and set a half-life limit of 1.1 × 10(25) years at the 90 per cent confidence level. The high sensitivity holds promise for further running of the EXO-200 detector and future 0νββ decay searches with an improved Xe-based experiment, nEXO.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The EXO-200 Collaboration is searching for neutrinoless double β decay using a liquid xenon (LXe) time projection chamber. This measurement relies on modeling the transport of charge deposits ...produced by interactions in the LXe to allow discrimination between signal and background events. Here we present measurements of the transverse diffusion constant and drift velocity of electrons at drift fields between 20 V/cm and 615 V/cm using EXO-200 data. At the operating field of 380 V/cm EXO-200 measures a drift velocity of 1.705+0.014 -0.010 mm/μs and a transverse diffusion coefficient of 55 ± 4 cm2/s.
The OPERA experiment was designed to search for ν_{μ}→ν_{τ} oscillations in appearance mode, i.e., by detecting the τ leptons produced in charged current ν_{τ} interactions. The experiment took data ...from 2008 to 2012 in the CERN Neutrinos to Gran Sasso beam. The observation of the ν_{μ}→ν_{τ} appearance, achieved with four candidate events in a subsample of the data, was previously reported. In this Letter, a fifth ν_{τ} candidate event, found in an enlarged data sample, is described. Together with a further reduction of the expected background, the candidate events detected so far allow us to assess the discovery of ν_{μ}→ν_{τ} oscillations in appearance mode with a significance larger than 5σ.
We present that the next-generation Enriched Xenon Observatory (nEXO) is a proposed experiment to search for neutrinoless double- β (0νββ) decay in 136Xe with a target half-life sensitivity of ...approximately 1028 yr using 5 × 103 kg of isotopically enriched liquid-xenon in a time projection chamber. This improvement of two orders of magnitude in sensitivity over current limits is obtained by a significant increase of the 136Xe mass, the monolithic and homogeneous configuration of the active medium, and the multiparameter measurements of the interactions enabled by the time projection chamber. Finally, the detector concept and anticipated performance are presented based upon demonstrated realizable background rates.
Summary
Background
Exposure to solar ultraviolet (UV) radiation is the main causative factor for skin cancer. Outdoor workers are at particular risk because they spend long working hours outside, may ...have little shade available and are bound to take their lunch at their workplace. Despite epidemiological evidence of a doubling in risk of squamous cell carcinoma (SCC) in outdoor workers, the recognition of skin cancer as an occupational disease remains scarce.
Objectives
To assess occupational solar UV doses and their contribution to skin cancer risk.
Methods
A numerical model (SimUVEx) was used to assess occupational and lunch break UV exposure, and to characterize exposure patterns and anatomical distribution. Risk of SCC was estimated from an existing epidemiological model.
Results
Horizontal body locations received 2·0–2·5 times more UV than vertical locations. The dose associated with having lunch outdoors every day was similar to that from doing outdoor work 1 day per week, but only half that of a seasonal worker. Outdoor work is associated with an increased risk of SCC and also with frequent acute episodes.
Conclusions
Occupational solar exposure contributes greatly to overall lifetime UV dose, resulting in an excess risk of SCC. The magnitude of the estimated excess in risk supports the recognition of SCC as an occupational disease.
What's already known about this topic?
Solar radiation is the most frequent occupational carcinogenic agent in many countries. It is also the main causative factor of skin cancer.
Skin cancer is barely recognized as an occupational disease due to a lack of data on the occupational contribution to the overall dose.
What does this study add?
We show the contribution of occupational ultraviolet exposure, in terms of annual (chronic) anatomical dose and acute events, to the risk of squamous cell carcinoma (SCC) for various occupational scenarios.
A numerical model (SimUVEx) was used to assess occupational and lunch break exposure, and to characterize exposure patterns and anatomical distribution.
Risk of SCC was estimated from an existing epidemiological model.
Characterization of the Hamamatsu VUV4 MPPCs for nEXO Gallina, G.; Giampa, P.; Retière, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2019, Letnik:
940, Številka:
C
Journal Article
Recenzirano
Odprti dostop
In this paper we report on the characterization of the Hamamatsu VUV4 (S/N: S13370-6152) Vacuum Ultra-Violet (VUV) sensitive Multi-Pixel Photon Counters (MPPC)s as part of the development of a ...solution for the detection of liquid xenon scintillation light for the nEXO experiment. Various MPPC features, such as: dark noise, gain, correlated avalanches, direct crosstalk and Photon Detection Efficiency (PDE) were measured in a dedicated setup at TRIUMF. MPPCs were characterized in the range 163K≤T≤233K. At an over voltage of 3.1±0.2 V and at T=163K we report a number of Correlated Avalanches (CAs) per pulse in the 1μs interval following the trigger pulse of 0.161±0.005. At the same settings the Dark-Noise (DN) rate is 0.137±0.002Hz/mm2. Both the number of CAs and the DN rate are within nEXO specifications. The PDE of the Hamamatsu VUV4 was measured for two different devices at T=233K for a mean wavelength of 189±7nm. At 3.6±0.2 V and 3.5±0.2 V of over voltage we report a PDE of 13.4±2.6% and 11±2%, corresponding to a saturation PDE of 14.8±2.8% and 12.2±2.3%, respectively. Both values are well below the 24% saturation PDE advertised by Hamamatsu. More generally, the second device tested at 3.5±0.2 V of over voltage is below the nEXO PDE requirement. The first one instead yields a PDE that is marginally close to meeting the nEXO specifications. This suggests that with modest improvements the Hamamatsu VUV4 MPPCs could be considered as an alternative to the FBK-LF Silicon Photo-Multipliers for the final design of the nEXO detector.
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