Wed·Apr 21, 2021Wednesday·April 21, 2021

1. 01*

   A new anomaly observed in ${}^4$He supports the existence of the hypothetical X17 particle

   A.J. Krasznahorkay🇭🇺 · M. Csatlós🇭🇺 · L. Csige🇭🇺 · J. Gulyás🇭🇺 · A. Krasznahorkay · B.M. Nyakó🇭🇺 · I. Rajta🇭🇺 · J. Timár🇭🇺 · I. Vajda🇭🇺 · N.J. Sas🇭🇺

   Energy-sum and angular correlation spectra of $e^{+}{e}^{-}$ pairs produced in the ${}^3$H(p,$\gamma$)${}^4$He nuclear reaction have been studied at $E_p$=510, 610 and 900 keV proton energies. The main features of the spectra can be understood by taking into account the internal and external pair creations following the direct proton radiative capture by ${}^3$H. However, these processes cannot account for the observed peak around 115${}^{\circ }$ in the angular correlation spectra. This anomalous excess of $e^{+}{e}^{-}$ pairs can be described by the creation and subsequent decay of a light particle during the direct capture process. The derived mass of the particle is $m_{\mathrm{X}}{c}^2$=16.94$\pm 0.12(stat)\pm 0.21(syst)$~MeV. According to the mass and branching ratio ($B_x=5.1(13)\times 10^{-6}$), this is likely the same X17 particle, which we recently suggested [Phys. Rev. Lett. 116, 052501 (2016)] for describing the anomaly observed in the decay of ${}^8$Be.

   nucl-exPRC(2021)·143 citations
2. 02*

   A D${}_2$O detector for flux normalization of a pion decay-at-rest neutrino source

   COHERENT Collaboration · D. Akimov🇷🇺 · P. An🇺🇸 · C. Awe🇺🇸 · P.S. Barbeau🇺🇸 · B. Becker🇺🇸 · V. Belov🇷🇺 · I. Bernardi🇺🇸 · M.A. Blackston🇺🇸 · L. Blokland🇺🇸 · A. Bolozdynya🇷🇺 · B. Cabrera-Palmer🇺🇸 and 67 other authors

   We report on the technical design and expected performance of a 592 kg heavy-water-Cherenkov detector to measure the absolute neutrino flux from the pion-decay-at-rest neutrino source at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). The detector will be located roughly 20 m from the SNS target and will measure the neutrino flux with better than 5% statistical uncertainty in 2 years. This heavy-water detector will serve as the first module of a two-module detector system to ultimately measure the neutrino flux to 2-3% at both the First Target Station and the planned Second Target Station of the SNS. This detector will significantly reduce a dominant systematic uncertainty for neutrino cross-section measurements at the SNS, increasing the sensitivity of searches for new physics.

   ↳ physics.ins-dethep-exnucl-exJINST(2021)·40 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.