Search

The nEXO neutrinoless double beta decay experiment is designed to use a time projection chamber and 5000 kg of isotopically enriched liquid xenon to search for the decay in $^{136}$Xe. Progress in the detector design, paired with higher fidelity in its simulation and an advanced data analysis, based on the one used for the final results of EXO-200, produce a sensitivity prediction that exceeds the half-life of $10^{28}$ years. Specifically, improvements have been made in the understanding of production of scintillation photons and charge as well as of their transport and reconstruction in the detector. The more detailed knowledge of the detector construction has been paired with more assays for trace radioactivity in different materials. In particular, the use of custom electroformed copper is now incorporated in the design, leading to a substantial reduction in backgrounds from the intrinsic radioactivity of detector materials. Furthermore, a number of assumptions from previous sensitivity projections have gained further support from interim work validating the nEXO experiment concept. Together these improvements and updates suggest that the nEXO experiment will reach a half-life sensitivity of $1.35\times 10^{28}$ yr at 90% confidence level in 10 years of data taking, covering the parameter space associated with the inverted neutrino mass ordering, along with a significant portion of the parameter space for the normal ordering scenario, for almost all nuclear matrix elements. The effects of backgrounds deviating from the nominal values used for the projections are also illustrated, concluding that the nEXO design is robust against a number of imperfections of the model., Comment: 26 pages, 19 figures, version accepted by Journal of Phys. G

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 $178\,\text{nm}$ xenon scintillation light, in order to achieve an energy resolution of $\sigma / Q_{\beta\beta} = 1\, \%$. 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 $175\,\text{nm}$ 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., Comment: 11 pages, 13 figures, 2 tables

The next-generation Enriched Xenon Observatory (nEXO) is a proposed experiment to search for neutrinoless double beta ($0\nu\beta\beta$) decay in $^{136}$Xe with a target half-life sensitivity of approximately $10^{28}$ years using $5\times10^3$ 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 $^{136}$Xe mass, the monolithic and homogeneous configuration of the active medium, and the multi-parameter measurements of the interactions enabled by the time projection chamber. The detector concept and anticipated performance are presented based upon demonstrated realizable background rates., Comment: v2 as published

A new design for the anode of a time projection chamber, consisting of a charge-detecting "tile", is investigated for use in large scale liquid xenon detectors. The tile is produced by depositing 60 orthogonal metal charge-collecting strips, 3~mm wide, on a 10~\si{\cm} $\times$ 10~\si{\cm} fused-silica wafer. These charge tiles may be employed by large detectors, such as the proposed tonne-scale nEXO experiment to search for neutrinoless double-beta decay. Modular by design, an array of tiles can cover a sizable area. The width of each strip is small compared to the size of the tile, so a Frisch grid is not required. A grid-less, tiled anode design is beneficial for an experiment such as nEXO, where a wire tensioning support structure and Frisch grid might contribute radioactive backgrounds and would have to be designed to accommodate cycling to cryogenic temperatures. The segmented anode also reduces some degeneracies in signal reconstruction that arise in large-area crossed-wire time projection chambers. A prototype tile was tested in a cell containing liquid xenon. Very good agreement is achieved between the measured ionization spectrum of a $^{207}$Bi source and simulations that include the microphysics of recombination in xenon and a detailed modeling of the electrostatic field of the detector. An energy resolution $\sigma/E$=5.5\% is observed at 570~\si{keV}, comparable to the best intrinsic ionization-only resolution reported in literature for liquid xenon at 936~V/\si{cm}., Comment: 18 pages, 13 figures, as published

Project SEE (Satellite Energy Exchange) is an international effort to develop a space-based mission for precise measurements of gravitation. Gravity is the missing link in unification theory. Because of the unique paucity of knowledge about this, the weakest of all known forces, and because gravity must have a key role in any unification theory, many aspects of gravity need to be understood in greater depth. A SEE mission would extend our knowledge of a number of gravitational parameters and effects, which are needed to test unification theories and various modern theories of gravity. SEE is a comprehensive gravitation experiment. A SEE mission would test for violations of the equivalence principle (EP), both by inverse-square-law (ISL) violations and by composition dependence (CD), both at ranges of the order of metres and at ranges on the order of RE. A SEE mission would also determine the gravitational constant G, test for time variation of G, and possibly test for post-Einsteinian orbital resonances. The potential finding of a non-zero time variation of G is perhaps the most important aspect of SEE. A SEE mission will also involve a search for new particles with very low masses, since any evidence of violations of the EP would be analysed in terms of a putative new Yukawa-like particle. Thus, SEE does not merely test for violations of general relativity (GR); SEE is a next-generation gravity mission.

Project SEE (Satellite Energy Exchange) is an international effort to organize a new space mission for fundamental measurements in gravitation, including tests of the equivalence principle (EP) by composition dependence (CD) and inverse-square-law (ISL) violations, determination of G, and a test for non-zero G-dot. The CD tests will be both at intermediate distances (a few metres) and at long distances (radius of the Earth, RE). Thus, a SEE mission would obtain accurate information self-consistently on a number of distinct gravitational effects. The EP test by CD at distances of a few metres would provide confirmation of earlier, more precise experiments. All other tests would significantly improve our knowledge of gravity. In particular, the error in G is projected to be less than 1 ppm. Project SEE entails launching a dedicated satellite and making detailed observations of free-floating test bodies within its experimental chamber.

The excitation energy per residue nucleon (E*/A) and fast and thermal light particle multiplicities are studied as a function of centrality defined as the number of grey tracks emitted N_grey and by the mean number of primary hadron-nucleon scatterings and mean impact parameter extracted from it. The value of E*/A and the multiplicities show an increase with centrality for all systems, 14.6 GeV p-Au and 8.0 GeV pi-Au and pbar-Au collisions, and the excitation energy per residue nucleon exhibits a uniform dependence on N_grey., Comment: 7 pages, 6 figures

A proposed space-based test of gravitational theory requires unique performance for thermometry and ranging instrumentation. The experiment involves a cylindrical test chamber in which two free-floating spherical test bodies are located. The test bodies are spheres which move relative to each other. The direction and rate of motion depend on the relative masses and orbit parameters mediated by the force of gravity. The experiment will determine Newton's gravitational constant, G; its time dependence, as well as investigate the equivalence principle, the inverse square law, and post- Einsteinian effects. The absolute value of the temperature at which the experiment is performed is not critical and may range anywhere from approximately 70 to 100 K. However, the experimental design calls for a temperature uniformity of approximately 0.001 K throughout the test volume. This is necessary in order to prevent radiation pressure gradients from perturbing the test masses. Consequently, a method is needed for verifying and establishing this test condition. The presentation is an assessment of the utility of phosphor-based thermometry for this application and a description of feasibility experiments. Phosphor thermometry is well suited for resolving minute temperature differences. The first tests in our lab have indicated the feasibility of achieving this desired temperature resolution.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.