Wed·Nov 13, 2024Wednesday·November 13, 2024

1. 01*

   Search for the X17 particle in ${}^7\mathrm{Li}(\mathrm{p},{\mathrm{e}}^{+}{\mathrm{e}}^{-}{)}^8\mathrm{Be}$ processes with the MEG II detector

   The MEG II collaboration: K. Afanaciev · A. M. Baldini · S. Ban · H. Benmansour · G. Boca · P. W. Cattaneo · G. Cavoto · F. Cei · M. Chiappini · A. Corvaglia · G. Dal Maso · A. De Bari and 54 other authors

   The observation of a resonance structure in the opening angle of the electron-positron pairs in the ${}^7$Li(p,\ee) ${}^8$Be reaction was claimed and interpreted as the production and subsequent decay of a hypothetical particle (X17). Similar excesses, consistent with this particle, were later observed in processes involving ${}^4$He and ${}^{12}$C nuclei with the same experimental technique. The MEG II apparatus at PSI, designed to search for the ${\mu }^{+}\to {\mathrm{e}}^{+}\gamma$ decay, can be exploited to investigate the existence of this particle and study its nature. Protons from a Cockroft-Walton accelerator, with an energy up to 1.1 MeV, were delivered on a dedicated Li-based target. The $\gamma$ and the e${}^{+}$e${}^{-}$ pair emerging from the ${}^8{\mathrm{Be}}^{\ast }$ transitions were studied with calorimeters and a spectrometer, featuring a broader angular acceptance than previous experiments. We present in this paper the analysis of a four-week data-taking in 2023 with a beam energy of 1080 keV, resulting in the excitation of two different resonances with Q-value \SI{17.6}{\mega\electronvolt} and \SI{18.1}{\mega\electronvolt}. No significant signal was found, and limits at \SI{90}{\percent} C.L. on the branching ratios (relative to the $\gamma$ emission) of the two resonances to X17 were set, $R_{17.6}<1.8\times 10^{-6}$ and $R_{18.1}<1.2\times 10^{-5}$.

   nucl-exhep-exEPJC(2025)·43 citations
2. 02*

   Investigation and optimization of the deconvolution method for PMT waveform reconstruction

   Jingzhe Tang🇨🇳 · Tianying Xiao🇨🇳 · Xuan Tang🇨🇳 · Yongbo Huang🇨🇳

   Photomultiplier tubes (PMTs) are extensively employed as photosensors in neutrino and dark matter detection. The precise charge and timing information extracted from the PMT waveform plays a crucial role in energy and vertex reconstruction. In this study, we investigate the deconvolution algorithm utilized for PMT waveform reconstruction, while enhancing the timing separation ability for pile-up hits by redesigning filters based on the time-frequency uncertainty principle. This filter design sacrifices signal-to-noise ratio (SNR) to achieve narrower pulse widths. Furthermore, we optimize the selection of signal pulses in the case of low SNR based on Short-Time Fourier Transform (STFT). Monte Carlo data confirms that our optimization yields enhanced reconstruction performance: improving timing separation ability for pile-up hits from $7\sim 10$~ns to $3\sim 5$~ns, while controlling the residual nonlinearity of charge reconstruction to about 1\% in the range of 0 to 20 photoelectrons.

   ↳ physics.ins-dethep-exnucl-exJINST(2025)·7 citations
3. 03*

   Nonlocal interaction and collective excitation in deuteron breakup on ${}^{24}$Mg nucleus

   A. Deltuva🇱🇹 · D. Jurčiukonis🇱🇹

   Deuteron breakup in collision with a ${}^{24}\mathrm{Mg}$ nucleus is studied using rigorous three-body scattering equations, extended to include also the excitation of the nucleus. Predictions based on local and nonlocal nucleon-nucleus optical potentials with rotational quadrupole deformation enabling the excitation of the ${}^{24}\mathrm{Mg}(2^{+})$ state are compared. The nonlocality effect is less pronounced than in the deuteron inelastic scattering ${}^{24}\mathrm{Mg}(d,d^{\prime })$ at the same energies, and manifests itself quite differently for semi-inclusive differential cross sections of elastic and inelastic breakup.

   ↳ nucl-thnucl-exPRC(2024)·1 citation
4. 04*

   High-Precision Excited-State Nuclear Recoil Spectroscopy with Superconducting Sensors

   C. Bray🇺🇸 · S. Fretwell🇺🇸 · L. A. Zepeda-Ruiz🇺🇸 · I. Kim🇺🇸 · A. Samanta🇺🇸 · K. Wang🇺🇸 · C. Stone-Whitehead🇺🇸 · W. K. Warburton · F. Ponce🇺🇸 · K. G. Leach🇺🇸 · R. Abells🇨🇦 · P. Amaro🇵🇹 and 21 other authors

   Superconducting sensors doped with rare isotopes have recently demonstrated powerful sensing performance for sub-keV radiation from nuclear decay. Here, we report the first high-resolution recoil spectroscopy of a single, selected nuclear state using superconducting tunnel junction (STJ) sensors. The STJ sensors were used to measure the eV-scale nuclear recoils produced in ${}^7$Be electron capture decay in coincidence with a 478 keV $\gamma$-ray emitted in decays to the lowest-lying excited nuclear state in ${}^7$Li. Details of the Doppler broadened recoil spectrum depend on the slow-down dynamics of the recoil ion. The measured spectral broadening is compared to empirical stopping power models as well as modern molecular dynamics simulations at low energy. The results have implications in several areas from nuclear structure and stopping powers at eV-scale energies to direct searches for dark matter, neutrino mass measurements, and other physics beyond the standard model.

   ↳ physics.ins-detnucl-ex2 citations
5. 05*

   Anthropogenic actinides in seawater and biota from the west coast of Sweden

   Mercedes López Lora · Elena Chamizo · Mats Eriksson

   The assessment of the origin of the anthropogenic contamination in marine regions impacted by other sources than global fallout is a challenge. This is the case of the west coast of Sweden, influenced by the liquid effluents released by the European Nuclear Reprocessing Plants through North Sea currents and by Baltic Sea local and regional sources, among others. This work focused on the study of anthropogenic actinides (${}^{236}$U, ${}^{237}$Np and ${}^{239,240}$Pu) in seawater and biota from a region close to Gothenburg where radioactive wastes with an unknown composition were dumped in 1964. To this aim, a radiochemical procedure for the sequential extraction of U, Np and Pu from biota samples and the subsequent analysis of ${}^{236}$U, ${}^{237}$Np, ${}^{239}$Pu and ${}^{240}$Pu by Accelerator Mass Spectrometry was developed. The method was validated through the study of two reference materials provided by the International Atomic Energy Agency (IAEA): IAEA-446 (Baltic Sea seaweed) and IAEA-437 (Mediterranean Sea mussels). The ${}^{233}$U$/{}^{236}$U atom ratio was also studied in the seawater samples. The obtained results indicate that the North Sea currents and global fallout are the major sources for ${}^{236}$U, ${}^{237}$Np and ${}^{239,240}$Pu to the studied area, with any clear evidence of other local sources. Complementary, information on the Concentrations Factors (CF) in biota was obtained, for which the available information is very scarce. For seaweed, CF values of $(4.1\pm 1.1)\times 10^3$, $88\pm 51$ and $70\pm 20$ have been obtained for Pu, Np and U, respectively. Lower CF values of $(3.6\pm 1.2)\times 10^2$, $37\pm 15$ and $15.1\pm 5.2$ for Pu, Np and U, respectively, have been obtained for mussels.

   ↳ physics.geo-phnucl-ex0 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.