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Register a new userDiscovery potential of multi-ton xenon detectors in neutrino electromagnetic properties
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Next-generation xenon detectors with multi-ton-year exposure are powerful direct probes of dark matter candidates, in particular the favorite weakly-interacting massive particles. Coupled with the features of low thresholds and backgrounds, they are also excellent telescopes of solar neutrinos. In this paper, we study the discovery potential of ton-scale xenon detectors in electromagnetic moments of solar neutrinos. Relevant neutrino-atom scattering processes are calculated by applying a state-of-the-arts atomic many-body method--relativistic random phase approximation (RRPA). Limits on these moments are derived from existing data and estimated with future experiment specifications. With one ton-year exposure, XENON-1T can improve the effective milli-charge constraint by a factor two. With LZ and DARWIN, the projected improvement on the solar neutrino effective milli-charge(magnetic moment) is around 7(2) times smaller than the current bound. If LZ can keep the same background level and push the electron recoil threshold to 0.5 keV, the projected improvement on milli-charge(magnetic moment) is about 10(3) times smaller than the current bound.
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The electromagnetic properties of neutrinos, which are either trivial or negligible in the context of the Standard Model, can probe new physics and have significant implications in astrophysics and cosmology. The current best direct limits on the neutrino millicharges and magnetic moments are both derived from data taken with germanium detectors with low thresholds at keV levels. In this paper, we discuss in detail a robust, ab initio method: the multiconfiguration relativistic random phase approximation, that enables us to reliably understand the germanium detector response at the sub-keV level, where atomic many-body physics matters. Using existing data with sub-keV thresholds, limits on reactor antineutrinos millicharge, magnetic moment, and charge radius squared are derived. The projected sensitivities for next generation experiments are also given and discussed.
We study the sensitivity of large-scale xenon detectors to low-energy solar neutrinos, to coherent neutrino-nucleus scattering and to neutrinoless double beta decay. As a concrete example, we consider the xenon part of the proposed DARWIN (Dark Matter WIMP Search with Noble Liquids) experiment. We perform detailed Monte Carlo simulations of the expected backgrounds, considering realistic energy resolutions and thresholds in the detector. In a low-energy window of 2-30 keV, where the sensitivity to solar pp and $^7$Be-neutrinos is highest, an integrated pp-neutrino rate of 5900 events can be reached in a fiducial mass of 14 tons of natural xenon, after 5 years of data. The pp-neutrino flux could thus be measured with a statistical uncertainty around 1%, reaching the precision of solar model predictions. These low-energy solar neutrinos will be the limiting background to the dark matter search channel for WIMP-nucleon cross sections below $sim$2$times$10$^{-48}$ cm$^2$ and WIMP masses around 50 GeV$cdot$c$^{-2}$, for an assumed 99.5% rejection of electronic recoils due to elastic neutrino-electron scatters. Nuclear recoils from coherent scattering of solar neutrinos will limit the sensitivity to WIMP masses below $sim$6 GeV$cdot$c$^{-2}$ to cross sections above $sim$4$times$10$^{-45}$cm$^2$. DARWIN could reach a competitive half-life sensitivity of 5.6$times$10$^{26}$ y to the neutrinoless double beta decay of $^{136}$Xe after 5 years of data, using 6 tons of natural xenon in the central detector region.
Available estimates for the energy resolution of DUNE vary by as much as a factor of four. To address this controversy, and to connect the resolution to the underlying physical processes, we build an independent simulation pipeline for neutrino events in liquid argon, combining the public tools GENIE and FLUKA. Using this pipeline, we first characterize the channels of non-hermeticity of DUNE, including subthreshold particles, charge recombination, and nuclear breakup. Particular attention is paid to the role of neutrons, which are responsible for a large fraction of missing energy in all channels. Next, we determine energy resolution, by quantifying event-to-event stochastic fluctuations in missing energy. This is done for several sets of assumptions about the reconstruction performance, including those available in the literature. The resulting migration matrices, connecting true and reconstructed neutrino energies, are presented. Finally, we quantify the impact of different improvements on the experimental performance. For example, we show that dropping particle identification information degrades the resolution by a factor of two, while omitting charge deposits from de-excitation gammas worsens it by about 25%. In the future, this framework can be used to assess the impact of cross section uncertainties on the oscillation sensitivity.
We study the sensitivity of detectors with directional sensitivity to coherent elastic neutrino-nucleus scattering (CE$ u$NS), and how these detectors complement measurements of the nuclear recoil energy. We consider stopped pion and reactor neutrino sources, and use gaseous helium and fluorine as examples of detector material. We generate Standard Model predictions, and compare to scenarios that include new, light vector or scalar mediators. We show that directional detectors can provide valuable additional information in discerning new physics, and we identify prominent spectral features in both the angular and the recoil energy spectrum for light mediators, even for nuclear recoil energy thresholds as high as $sim 50$ keV. Combined with energy and timing information, directional information can play an important role in extracting new physics from CE$ u$NS experiments.
Future dark matter (DM) direct detection searches will be subject to irreducible neutrino backgrounds that will challenge the identification of an actual WIMP signal in experiments without directionality sensitivity. We study the impact of neutrino-quark non-standard interactions (NSI) on this background, assuming the constraints from neutrino oscillations and the recent COHERENT experiment data, which are relevant for NSI mediated by light mediators, $m_{rm med} lesssim{cal O}$(GeV). We calculate the expected number of neutrino-nucleus elastic scattering events in a Xe-based ton-size dark matter detector, including solar neutrino fluxes from the $pp$ chain and CNO cycle as well as sub-GeV atmospheric fluxes and taking into account NSI effects in both propagation and detection. We find that sizable deviations from the standard model expectation are possible, but are more pronounced for flavor-diagonal couplings, in particular for electron neutrinos. We show that neutrino NSI can enhance or deplete the neutrino-nucleus event rate, which may impact DM searches in multi-ton detectors.
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