Marcello Messina

We report on a search for sub-GeV dark matter upscattered via the solar reflection mechanism in the heavy mediator scenario. Under the standard halo model, keV–MeV dark matter produces nuclear recoils with energies below the detection threshold of liquid xenon time projection chambers. We enhance sensitivity to low-mass dark matter (DM) by considering dark matter–electron scattering, employing dedicated event selections to reduce the detection threshold and exploiting the additional kinetic energy imparted to the dark matter particle by solar upscattering. Using XENON1T ionization-only and XENONnT low-energy electronic recoil datasets, we exclude previously unconstrained DM-electron scattering cross section for masses between 4.6 and 20 keV / c 2 and between 0.2 and 2 MeV / c 2 , reaching a minimum of 3.41 × 10 − 39 cm 2 for a mass of 0.3 MeV / c 2 at 90% confidence level.

We present a study of the energy resolution of transition-edge sensors (TESs) for the detection of electrons in the 100-eV kinetic energy range. The TES is a Ti-Au bilayer with an active area of ( 60 × 60 ) μ m 2 and a critical temperature of approximately 80 mK . The electron source is based on vertically aligned multiwall carbon nanotubes located inside the cryostat, with electrons generated via field emission. For electrons in the ( 92 – 99 ) eV kinetic energy range, we obtain a Gaussian energy resolution for fully absorbed electrons of ( 0.48 ± 0.04 ± 0.06 ) eV , where the first uncertainty is statistical and the second systematic. When considering the full-width at half-maximum of the peak of the signal amplitude distribution, the corresponding resolution is of ( 1.4 ± 0.2 ± 0.3 ) eV . The former represents an improvement of ( 47 – 60 ) % with respect to previous results and is mainly attributed to the reduction in the TES active area. The latter is instead an improvement of over a factor of 21 and is mainly due to the reduction in the emitting area of the electron source, which significantly suppresses electron back-scattering in proximity of the TES. These results represent a major milestone toward high-precision spectroscopy on low-energy electrons, which is a key objective for the PTOLEMY experiment.

We report a 3.3 σ measurement of coherent elastic neutrino-nucleus scattering from solar B 8 neutrinos using a 6.77 t × yr exposure from the XENONnT experiment, inferring a solar B 8 neutrino flux of ( 5 − 2 + 3 ) × 10 6 cm − 2 s − 1 , consistent with previous measurements. In the presence of the B 8 “neutrino fog,” we find no evidence for light dark matter, and observe diminishing returns in sensitivity with increasing exposure. A 93% increase in exposure from the previous search improves the median sensitivity to the nucleon scattering cross section for a 5 GeV / c 2 spin-independent weakly interacting massive particle by 10%. The dataset was also used to measure the weak mixing angle at ∼ 0.02 GeV / c momentum transfer and constrain physics beyond the Standard Model.

Characterizing low-energy, keV-range nuclear recoils near the detector threshold is one of the major challenges for large direct dark matter detectors. To that end, we have successfully used an Yttrium-Beryllium photoneutron source that emits 152 keV neutrons for the calibration of the light and charge yields of the XENONnT experiment for the first time. After data selection, we accumulated 474 events from 183 hours of exposure with this source. The expected background was 55 ± 12 accidental coincidence events, estimated using a dedicated 152 hour background calibration run with a Yttrium-PVC gamma-only source and data-driven modeling. From these calibrations, we extracted the light (charge) yield for liquid xenon at our field strength of 23 V / cm between 0.3 (0.7) keV NR and 5.0 keV NR . This calibration is crucial for accurately measuring the solar B 8 neutrino coherent elastic neutrino-nucleus scattering and searching for light dark matter particles with masses below 12 GeV / c 2 .

We report on the search for x-ray radiation as predicted from dynamical quantum collapse with low-energy electronic recoil data in the energy range of 1–140 keV from the first science run of the XENONnT dark matter detector. Spontaneous radiation is an unavoidable effect of dynamical collapse models, which were introduced as a possible solution to the long-standing measurement problem in quantum mechanics. The analysis utilizes a model that for the first time accounts for cancellation effects in the emitted spectrum, which arise in the x-ray range due to the opposing electron-proton charges in xenon atoms. New world-leading limits on the free parameters of the Markovian continuous spontaneous localization and Diósi-Penrose models are set, improving previous best constraints by two orders of magnitude and a factor of five, respectively. For the strength and correlation length of the continuous spontaneous localization model, values in the originally proposed parameter ranges are experimentally excluded for the first time.

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 report the measurement of the $^{214}$Bi beta-decay spectrum to the ground state of $^{214}$Po using the XENONnT detector. This decay is classified as first-forbidden non-unique, for which theoretical predictions require detailed nuclear structure modeling. A dedicated identification algorithm isolates a high-purity sample of ground-state beta-decays, explicitly excluding events with associated gamma-rays emission. By comparing the measured spectrum, which covers energies up to 3.27 MeV, with several nuclear models, we find that the prediction based on the conserved vector current (CVC) hypothesis provides the best description of the data. Using this dataset, we additionally derive charge and light yield curves for electronic recoils, extending detector response modeling up to the MeV scale.