Wed·Jan 31, 2024Wednesday·January 31, 2024

1. 01*

   Mass, spectroscopy and two-neutron decay of ${}^{16}$Be

   B. Monteagudo🇫🇷 · F.M. Marqués🇫🇷 · J. Gibelin🇫🇷 · N.A. Orr🇫🇷 · A. Corsi🇫🇷 · Y. Kubota🇯🇵 · J. Casal🇮🇹 · J. Gómez-Camacho🇪🇸 · G. Authelet🇫🇷 · H. Baba🇯🇵 · C. Caesar🇩🇪 · D. Calvet🇫🇷 and 56 other authors

   The structure and decay of the most neutron-rich beryllium isotope, ${}^{16}$Be, has been investigated following proton knockout from a high-energy ${}^{17}$B beam. Two relatively narrow resonances were observed for the first time, with energies of $0.84(3)$ and $2.15(5)$ MeV above the two-neutron decay threshold and widths of $0.32(8)$ and $0.95(15)$ MeV respectively. These were assigned to be the ground ($J^{\pi }=0^{+}$) and first excited ($2^{+}$) state, with $E_x=1.31(6)$ MeV. The mass excess of ${}^{16}$Be was thus deduced to be $56.93(13)$ MeV, some $0.5$ MeV more bound than the only previous measurement. Both states were observed to decay by direct two-neutron emission. Calculations incorporating the evolution of the wavefunction during the decay as a genuine three-body process reproduced the principal characteristics of the neutron-neutron energy spectra for both levels, indicating that the ground state exhibits a strong spatially compact dineutron component, while the 2${}^{+}$ level presents a far more diffuse neutron-neutron distribution.

   nucl-exnucl-thPRL(2024)·20 citations
2. 02*

   Compton Scattering on 4He with Nuclear One- and Two-Body Densities

   Harald W. Griesshammer (George Washington U.)🇺🇸 · Junjie Liao (George Washington U.)🇺🇸 · Judith A. McGovern (U. of Manchester)🇬🇧 · Andreas Nogga (FZ Jülich)🇩🇪 · Daniel R. Phillips (Ohio U.)🇺🇸

   We present the first \emph{ab initio} calculation of elastic Compton scattering from 4He. It is carried out to $\mathcal{O}(e^2{\delta }^3)$ [N3LO] in the $\delta$ expansion of $\chi$EFT. At this order and for this target, the only free parameters are the scalar-isoscalar electric and magnetic dipole polarisabilities of the nucleon. Adopting current values for these yields a parameter-free prediction. This compares favourably with the world data from HI$\gamma$S, Illinois and Lund for photon energies $50\mathrm{MeV}\lesssim \omega \lesssim 120\mathrm{MeV}$ within our theoretical uncertainties of $\pm 10\%$. We predict a cross section up to 7 times that for deuterium. As in 3He, this emphasises and tests the key role of meson-exchange currents between np pairs in Compton scattering on light nuclei. We assess the sensitivity of the cross section and beam asymmetry to the nucleon polarisabilities, providing clear guidance to future experiments seeking to further constrain them. The calculation becomes tractable by use of the Transition Density Method. The one- and two-body densities generated from 5 chiral potentials and the AV18$+$UIX potential are available using the python package provided at \url{https://pypi.org/project/nucdens/}.

   ↳ nucl-thnucl-exEPJA(2024)·6 citations
3. 03*

   Analysis of neutron time-of-flight spectra with a Bayesian unfolding methodology

   A. Pérez de Rada Fiol · D. Cano-Ott🇪🇸 · T. Martínez🇪🇸 · V. Alcayne🇪🇸 · E. Mendoza🇪🇸 · J. Plaza🇪🇸 · A. Sanchez-Caballero🇪🇸 · D. Villamarín🇪🇸

   We have developed an innovative methodology for obtaining the neutron energy distribution from a time-of-flight (TOF) measurement based on the iterative Bayesian unfolding method and accurate Monte Carlo simulations. This methodology has been validated through the analysis of a realistic virtual $\beta$-decay experiment, including the most relevant systematic effects in a real experiment. The proposed methodology allowed for obtaining accurate results over the energy range above the neutron detection threshold.

   ↳ physics.data-annucl-exRadiat.Phys.Chem.(2025)·2 citations
4. 04*

   Tractable $T$-matix model for reaction processes in muon catalyzed fusion $(dt\mu {)}_{J=v=0}\to \alpha +n+\mu +17.6\mathrm{MeV}\text{mbox}or(\alpha \mu {)}_{nl}+n+17.6\mathrm{MeV}$

   Qian Wu🇨🇳 · Masayasu Kamimura

   Reaction processes in muon catalyzed fusion ($\mu$CF), $(dt\mu {)}_{J=v=0}\to \alpha +n+\mu +17.6\mathrm{MeV}$ or $(\alpha \mu {)}_{nl}+n+17.6\mathrm{MeV}$ in the D-T mixture was comprehensively studied by Kamimura, Kino and Yamashita [Phys. Rev. C 107, 034607 (2023)] by solving the $dt\mu$-$\alpha n\mu$ coupled channel (CC) Schrödinger equation under a boundary condition where the muonic molecule $(dt\mu {)}_{J=v=0}$ was set as the initial state and the outgoing wave was in the $\alpha n\mu$ channel. We approximate this CC framework and propose a considerably more tractable model using the $T$-matrix method based on the Lippmann-Schwinger equation. Nuclear interactions adopted in the $T$-matrix model are determined by reproducing the cross section of the reaction $d+t\to \alpha +n+17.6\mathrm{MeV}$ at low energies. The cross section of the strong-coupling rearrangement reaction is presented in a simple closed form based on our new model. This $T$-matrix model have reproduced most of the calculated results on the above $\mu$CF reaction reported by Kamimura et al. (2023) and is applicable to other $\mu$CF systems such as $(dd\mu )$, $(tt\mu )$, $(dt\mu {)}^{\ast }$, $(dd\mu {)}^{\ast }$.

   ↳ nucl-thnucl-exphysics.atm-clusPRC(2024)·7 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.