We present the first measurement of nuclear recoils from solar B 8 neutrinos via coherent elastic neutrino-nucleus scattering with the XENONnT dark matter experiment. The central detector of XENONnT is a low-background, two-phase time projection chamber with a 5.9 t sensitive liquid xenon target. A blind analysis with an exposure of 3.51 t × yr resulted in 37 observed events above 0.5 keV, with ( 26.4 − 1.3 + 1.4 ) events expected from backgrounds. The background-only hypothesis is rejected with a statistical significance of 2.73 σ . The measured B 8 solar neutrino flux of ( 4.7 − 2.3 + 3.6 ) × 10 6 cm − 2 s − 1 is consistent with results from the Sudbury Neutrino Observatory. The measured neutrino flux-weighted CE ν NS cross section on Xe of ( 1.1 − 0.5 + 0.8 ) × 10 − 39 cm 2 is consistent with the Standard Model prediction. This is the first direct measurement of nuclear recoils from solar neutrinos with a dark matter detector. Published by the American Physical Society 2024

The multi-staged XENON program at INFN Laboratori Nazionali del Gran Sasso aims to detect dark matter with two-phase liquid xenon time projection chambers of increasing size and sensitivity. The XENONnT experiment is the latest detector in the program, planned to be an upgrade of its predecessor XENON1T. It features an active target of 5.9 tonnes of cryogenic liquid xenon (8.5 tonnes total mass in cryostat). The experiment is expected to extend the sensitivity to WIMP dark matter by more than an order of magnitude compared to XENON1T, thanks to the larger active mass and the significantly reduced background, improved by novel systems such as a radon removal plant and a neutron veto. This article describes the XENONnT experiment and its sub-systems in detail and reports on the detector performance during the first science run.

We report on a search for weakly interacting massive particle (WIMP) dark matter (DM) via elastic DM-xenon-nucleus interactions in the XENONnT experiment. We combine datasets from the first and second science campaigns resulting in a total exposure of 3.1 tonne-years. In a blind analysis of nuclear recoil events with energies above 3.8 keV NR , we find no significant excess above background. We set new upper limits on the spin-independent WIMP-nucleon scattering cross section for WIMP masses above 10 GeV / c 2 with a minimum of 1.7 × 10 − 47 cm 2 at 90% confidence level for a WIMP mass of 30 GeV / c 2 . We achieve a best median sensitivity of 1.4 × 10 − 47 cm 2 for a 41 GeV / c 2 WIMP. Compared to the result from the first XENONnT science dataset, we improve our sensitivity by a factor of up to 1.8.

We search for dark matter (DM) with a mass [ 3 , 12 ] GeV / c 2 using an exposure of 3.51 tonne year with the XENONnT experiment. We consider spin-independent DM-nucleon interactions mediated by a heavy or light mediator, spin-dependent DM-neutron interactions, momentum-dependent DM scattering, and mirror DM. Using a lowered energy threshold compared to the previous weakly interacting massive particle search, a blind analysis of [0.5, 5.0] keV nuclear recoil events reveals no significant signal excess over the background. XENONnT excludes spin-independent DM-nucleon cross sections > 2.5 × 10 − 45 cm 2 at 90% confidence level for 6 GeV / c 2 DM. In the considered mass range, the DM sensitivity approaches the “neutrino fog,” the limitation where neutrinos produce a signal that is indistinguishable from that of light DM-xenon nucleus scattering.

We report on a blinded search for dark matter with single- and few-electron signals in the first science run of XENONnT relying on a novel detector response framework that is physics model dependent. We derive 90% confidence upper limits for dark matter-electron interactions. Heavy and light mediator cases are considered for the standard halo model and dark matter up-scattered in the Sun. We set stringent new limits on dark matter-electron scattering via a heavy mediator with a mass within 10 – 20 MeV / c 2 and electron absorption of axionlike particles and dark photons for m χ below 0.03 keV / c 2 .

While the international nEDM collaboration at the Paul Scherrer Institut (PSI) took data in 2017 that covered a considerable fraction of the parameter space of claimed potential signals of hypothetical neutron (n) to mirror-neutron ($n^{\prime }$) transitions, it could not test all claimed signal regions at various mirror magnetic fields. Therefore, a new study of $n-n^{\prime }$ oscillations using stored ultracold neutrons (UCNs) is underway at PSI, considerably expanding the reach in parameter space of mirror magnetic fields ($B^{\prime }$) and oscillation time constants (${\tau }_{n{n}^{\prime }}$). The new apparatus is designed to test for the anomalous loss of stored ultracold neutrons as a function of an applied magnetic field. The experiment is distinguished from its predecessors by its very large storage vessel (1.47 m³), enhancing its statistical sensitivity. In a test experiment in 2020 we have demonstrated the capabilities of our apparatus. However, the full analysis of our recent data is still pending. Based on already demonstrated performance, we will reach sensitivity to oscillation times ${\tau }_{n{n}^{\prime }}/\sqrt{cos\left(\beta \right)}$ well above a hundred seconds, with $\beta$ being the angle between $B^{\prime }$ and the applied magnetic field B. The scan of B will allow the finding or the comprehensive exclusion of potential signals reported in the analysis of previous experiments and suggested to be consistent with neutron to mirror-neutron oscillations.