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1. Properties of Cosmic Deuterons Measured by the Alpha Magnetic Spectrometer

   https://doi.org/10.1103/PhysRevLett.132.261001  

   Aguilar, M; Alpat, B; Ambrosi, G; Anderson, H; Arruda, L; Attig, N; Bagwell, C; Barao, F; Barbanera, M; Barrin, L; et al (June 2024, Physical Review Letters)

   Precision measurements by the Alpha Magnetic Spectrometer (AMS) on the International Space Station of the deuteron ( $D$ ) flux are presented. The measurements are based on $21\times {10}^6$ $D$ nuclei in the rigidity range from 1.9 to 21 GV collected from May 2011 to April 2021. We observe that over the entire rigidity range the $D$ flux exhibits nearly identical time variations with the $p$ , ${}^3\mathrm{He}$ , and ${}^4\mathrm{He}$ fluxes. Above 4.5 GV, the $D/{}^4\mathrm{He}$ flux ratio is time independent and its rigidity dependence is well described by a single power law $\propto R^{\mathrm{\Delta }}$ with ${\mathrm{\Delta }}_{D/{}^4\mathrm{He}}=-0.108\pm 0.005$ . This is in contrast with the ${}^3\mathrm{He}/{}^4\mathrm{He}$ flux ratio for which we find ${\mathrm{\Delta }}_{{}^3\mathrm{He}/{}^4\mathrm{He}}=-0.289\pm 0.003$ . Above $\sim 13\mathrm{GV}$ we find a nearly identical rigidity dependence of the $D$ and $p$ fluxes with a $D/p$ flux ratio of $0.027\pm 0.001$ . These unexpected observations indicate that cosmic deuterons have a sizable primarylike component. With a method independent of cosmic ray propagation, we obtain the primary component of the $D$ flux equal to $9.4\pm 0.5\%$ of the ${}^4\mathrm{He}$ flux and the secondary component of the $D$ flux equal to $58\pm 5\%$ of the ${}^3\mathrm{He}$ flux. Published by the American Physical Society2024 

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2. Shedding Light on the Origin of ${}^{204}\mathrm{Pb}$ , the Heaviest $s$ -Process–Only Isotope in the Solar System

   https://doi.org/10.1103/PhysRevLett.133.052702  

   Casanovas-Hoste, A; Domingo-Pardo, C; Lerendegui-Marco, J; Guerrero, C; Tarifeño-Saldivia, A; Krtička, M; Pignatari, M; Calviño, F; Schumann, D; Heinitz, S; et al (July 2024, Physical Review Letters)

   Asymptotic giant branch stars are responsible for the production of most of the heavy isotopes beyond Sr observed in the solar system. Among them, isotopes shielded from the $r$ -process contribution by their stable isobars are defined as $s$ -only nuclei. For a long time the abundance of ${}^{204}\mathrm{Pb}$ , the heaviest $s$ -only isotope, has been a topic of debate because state-of-the-art stellar models appeared to systematically underestimate its solar abundance. Besides the impact of uncertainties from stellar models and galactic chemical evolution simulations, this discrepancy was further obscured by rather divergent theoretical estimates for the neutron capture cross section of its radioactive precursor in the neutron-capture flow, ${}^{204}\mathrm{Tl}$ ( $t_{1/2}=3.78\mathrm{yr}$ ), and by the lack of experimental data on this reaction. We present the first ever neutron capture measurement on ${}^{204}\mathrm{Tl}$ , conducted at the CERN neutron time-of-flight facility n_TOF, employing a sample of only 9 mg of ${}^{204}\mathrm{Tl}$ produced at the Institute Laue Langevin high flux reactor. By complementing our new results with semiempirical calculations we obtained, at the $s$ -process temperatures of $kT\approx 8\mathrm{keV}$ and $kT\approx 30\mathrm{keV}$ , Maxwellian-averaged cross sections (MACS) of 580(168) mb and 260(90) mb, respectively. These figures are about 3% lower and 20% higher than the corresponding values widely used in astrophysical calculations, which were based only on theoretical calculations. By using the new ${}^{204}\mathrm{Tl}$ MACS, the uncertainty arising from the ${}^{204}\mathrm{Tl}(\mathrm{n},\gamma )$ cross section on the $s$ -process abundance of ${}^{204}\mathrm{Pb}$ has been reduced from $\sim 30\%$ down to $+8\%/-6\%$ , and the $s$ -process calculations are in agreement with the latest solar system abundance of ${}^{204}\mathrm{Pb}$ reported by K. Lodders in 2021. Published by the American Physical Society2024 

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3. First Indication of Solar ${}^8\mathrm{B}$ Neutrinos via Coherent Elastic Neutrino-Nucleus Scattering with XENONnT

   https://doi.org/10.1103/PhysRevLett.133.191002  

   Aprile, E; Aalbers, J; Abe, K; Ahmed_Maouloud, S; Althueser, L; Andrieu, B; Angelino, E; Antón_Martin, D; Arneodo, F; Baudis, L; et al (November 2024, Physical Review Letters)

   We present the first measurement of nuclear recoils from solar ${}^8\mathrm{B}$ 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 $3.51\mathrm{t}\times \mathrm{yr}$ 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 $2.73\sigma$ . The measured ${}^8\mathrm{B}$ solar neutrino flux of $\left({4.7}_{-2.3}^{+3.6}\right)\times {10}^6{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ is consistent with results from the Sudbury Neutrino Observatory. The measured neutrino flux-weighted $\mathrm{CE}\nu \mathrm{NS}$ cross section on Xe of $\left({1.1}_{-0.5}^{+0.8}\right)\times {10}^{-39}{\mathrm{cm}}^2$ 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 Society2024 

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4. Offline tagging of radon-induced backgrounds in XENON1T and applicability to other liquid xenon time projection chambers

   https://doi.org/10.1103/PhysRevD.110.012011  

   Aprile, E; Aalbers, J; Abe, K; Ahmed_Maouloud, S; Althueser, L; Andrieu, B; Angelino, E; Angevaare, J R; Antón_Martin, D; Arneodo, F; et al (July 2024, Physical Review D)

   This paper details the first application of a software tagging algorithm to reduce radon-induced backgrounds in liquid noble element time projection chambers, such as XENON1T and XENONnT. The convection velocity field in XENON1T was mapped out using ${}^{222}\mathrm{Rn}$ and ${}^{218}\mathrm{Po}$ events, and the rms convection speed was measured to be $0.30\pm 0.01\mathrm{cm}/\mathrm{s}$ . Given this velocity field, ${}^{214}\mathrm{Pb}$ background events can be tagged when they are followed by ${}^{214}\mathrm{Bi}$ and ${}^{214}\mathrm{Po}$ decays, or preceded by ${}^{218}\mathrm{Po}$ decays. This was achieved by evolving a point cloud in the direction of a measured convection velocity field, and searching for ${}^{214}\mathrm{Bi}$ and ${}^{214}\mathrm{Po}$ decays or ${}^{218}\mathrm{Po}$ decays within a volume defined by the point cloud. In XENON1T, this tagging system achieved a ${}^{214}\mathrm{Pb}$ background reduction of ${6.2}_{-0.9}^{+0.4}\%$ with an exposure loss of $1.8\pm 0.2\%$ , despite the timescales of convection being smaller than the relevant decay times. We show that the performance can be improved in XENONnT, and that the performance of such a software-tagging approach can be expected to be further improved in a diffusion-limited scenario. Finally, a similar method might be useful to tag the cosmogenic ${}^{137}\mathrm{Xe}$ background, which is relevant to the search for neutrinoless double-beta decay. Published by the American Physical Society2024 

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5. Measurement of the Isolated Nuclear Two-Photon Decay in ${}^{72}\mathrm{Ge}$

   https://doi.org/10.1103/PhysRevLett.133.022502  

   Freire-Fernández, D; Korten, W; Chen, R J; Litvinov, S; Litvinov, Yu A; Sanjari, M S; Weick, H; Akinci, F C; Albers, H M; Armstrong, M; et al (July 2024, Physical Review Letters)

   The nuclear two-photon or double-gamma ( $2\gamma$ ) decay is a second-order electromagnetic process whereby a nucleus in an excited state emits two gamma rays simultaneously. To be able to directly measure the $2\gamma$ decay rate in the low-energy regime below the electron-positron pair-creation threshold, we combined the isochronous mode of a storage ring with Schottky resonant cavities. The newly developed technique can be applied to isomers with excitation energies down to $\sim 100\mathrm{keV}$ and half-lives as short as $\sim 10\mathrm{ms}$ . The half-life for the $2\gamma$ decay of the first-excited $0^{+}$ state in bare ${}^{72}\mathrm{Ge}$ ions was determined to be 23.9(6) ms, which strongly deviates from expectations. Published by the American Physical Society2024 

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