Thu·Apr 24, 2025Thursday·April 24, 2025

1. 01*

   Particles in finite volumes and a toy model of decaying neutrons

   Christian Käding🇦🇹

   It is well-known that the momentum spectra of particles confined to finite spatial volumes deviate from the continuous spectra used for unconfined particles. In this article, we consider real scalar particles confined to finite volumes with periodic boundary conditions, such that the particles' spectra are discrete. We directly compute the density matrices describing the decay processes $\varphi \to {\phi }^2$ and $\varphi \to \phi \chi \nu$, and subsequently derive expressions for the decay probabilities both for confined and unconfined particles. The latter decay process is used as a rough toy model for a neutron decaying into a proton, an electron, and an anti-electron neutrino. We propose that finite volume effects can have an impact on the outcomes of experiments measuring the neutron lifetime. In addition, our findings at the toy model level suggest that taking into account possible initial correlations between neutrons and their daughter particles might be relevant as well.

   ↳ hep-phhep-thnucl-exnucl-th+1EPJC(2025)·2 citations
2. 02*

   Characterization of a GAGG detector for neutron measurements in underground laboratories

   Lorenzo Ascenzo🇮🇹 · Giovanni Benato🇮🇹 · Yingjie Chu🇮🇹 · Giuseppe Di Carlo🇮🇹 · Andrea Molinario🇮🇹 · Silvia Vernetto🇮🇹

   In rare events experiments, such as those devoted to the direct search of dark matter, a precise knowledge of the environmental gamma and neutron backgrounds is crucial for reaching the design experiment sensitivity. The neutron component is often poorly known due to the lack of a scalable detector technology for the precise measurement of low-flux neutron spectra. Gd${}_3$Al${}_2$Ga${}_3$O${}_{12}$ (GAGG) is a newly developed, high-density scintillating crystal with a high gadolinium content, which could allow to exploit the high $(n,\gamma )$ cross section of ${}^{155}$Gd and ${}^{157}$Gd for neutron measurements in underground environments. GAGG crystals feature a high scintillation light yield, good timing performance, and the capability of particle identification via pulse-shape discrimination. In a low-background environment, the distinctive signature produced by neutron capture on gadolinium, namely a $\beta /\gamma$ cascade releasing up to 9 MeV of total energy, and the efficient particle identification provided by GAGG could yield a background-free neutron capture signal. In this work, we present the characterization of a first GAGG detector prototype in terms of particle discrimination performance, intrinsic radioactive contamination, and neutron response.

   ↳ physics.ins-detnucl-exEPJC(2025)·2 citations
3. 03*

   Performance of the MORA Apparatus for Testing Time-Reversal Invariance in Nuclear Beta Decay

   N. Goyal🇫🇷 · A. Singh🇫🇷 · S. Daumas-Tschopp🇫🇷 · L. M. Motilla Martinez🇫🇷 · G. Ban🇫🇷 · V. Bosquet🇫🇷 · J. F. Cam🇫🇷 · P. Chauveau🇫🇷 · S. Chinthakayala🇫🇷 · G. Fremont🇫🇷 · R.P. De Groote🇧🇪 · F. de Oliveira Santos🇫🇷 and 31 other authors

   The MORA experimental setup is designed to measure the triple-correlation D parameter in nuclear beta decay. The D coefficient is sensitive to possible violations of time-reversal invariance. The experimental configuration consists of a transparent Paul trap surrounded by a detection setup with alternating beta and recoil-ion detectors. The octagonal symmetry of the detection setup optimizes the sensitivity of positron-recoil-ion coincidence rates to the D correlation, while reducing systematic effects. MORA utilizes an innovative in-trap laser polarization technique. The design and performance of the ion trap, associated beamline elements, lasers and beta and recoil-ion detectors, are presented. Recent progress towards the polarization proof-of-principle is described.

   ↳ physics.ins-detnucl-exEPJA(2025)·1 citation
4. 04*

   Baryon Number Violation: From Nuclear Matrix Elements to BSM Physics

   Leah J. Broussard🇺🇸 · Andreas Crivellin🇨🇭 · Martin Hoferichter🇨🇭 · Sergey Syritsyn🇺🇸 · Yasumichi Aoki🇯🇵 · Joshua L. Barrow🇺🇸 · Arnau Bas i Beneito🇪🇸 · Zurab Berezhiani🇮🇹 · Nicola Fulvio Calabria🇮🇹 · Svjetlana Fajfer🇸🇮 · Susan Gardner🇺🇸 · Julian Heeck🇺🇸 and 10 other authors

   Processes that violate baryon number, most notably proton decay and $n\bar{n}$ transitions, are promising probes of physics beyond the Standard Model (BSM) needed to understand the lack of antimatter in the Universe. To interpret current and forthcoming experimental limits, theory input from nuclear matrix elements to UV complete models enters. Thus, an interplay of experiment, effective field theory, lattice QCD, and BSM model building is required to develop strategies to accurately extract information from current and future data and maximize the impact and sensitivity of next-generation experiments. Here, we briefly summarize the main results and discussions from the workshop "INT-25-91W: Baryon Number Violation: From Nuclear Matrix Elements to BSM Physics," held at the Institute for Nuclear Theory, University of Washington, Seattle, WA, January 13-17, 2025.

   ↳ hep-phhep-exhep-latnucl-ex+1J.Phys.G(2025)·10 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.