Thu·Jul 6, 2023Thursday·July 6, 2023

1. 01*

   X17 discovery potential from $\gamma D\to e^{+}{e}^{-}pn$ with neutron tagging

   Cornelis J.G. Mommers🇩🇪 · Marc Vanderhaeghen🇩🇪

   We propose a novel direct search experiment for X17 using the reaction $\gamma D\to e^{+}{e}^{-}pn$. X17 is a hypothetical particle conjectured by the ATOMKI collaboration to explain anomalous signals around 17 MeV in excited ${}^8$Be, ${}^4$He and ${}^{12}$C nuclear decays via internal pair creation. It has been subject to a global experimental and theoretical research program. The proposed direct search in $\gamma D\to e^{+}{e}^{-}pn$ can verify the existence of X17 through the production on a quasi-free neutron, and determine its quantum numbers separate from ongoing and planned nuclear-decay experiments. This is especially timely in view of the theoretical tension between results from the ${}^{12}$C and ${}^8$Be measurements. Using the plane-wave impulse approximation, we quantify the expected signal and background for pseudoscalar, vector and axial-vector X17 scenarios. We optimize the kinematics for the quasi-free neutron region with the upcoming MAGIX experiment at MESA in mind and show that for all three scenarios the X17 signal is clearly visible above the QED background.

   ↳ hep-phnucl-exnucl-th2 citations
2. 02*

   Collision integral with momentum-dependent potentials and its impact on pion production in heavy-ion collisions

   Natsumi Ikeno🇯🇵 · Akira Ono🇯🇵

   The momentum dependence of the nucleon mean-field potential in a wide momentum range can be an important factor to determine the $\Delta$ resonance and pion production in intermediate-energy heavy-ion collisions. In particular, in neutron-rich systems such as ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ collisions, we need to carefully treat the momentum dependence because the neutron and proton potentials can have different momentum dependence, as characterized at low momenta by effective masses. In the present work, we rigorously calculate the collision terms of $NN\leftrightarrow N\Delta$ and $\Delta \leftrightarrow N\pi$ processes with the precise conservation of energy and momentum under the presence of momentum-dependent potentials for the initial and final particles of the process. The potentials affect not only the threshold condition for the process but also the cross section in general as a function of the momenta of the initial particles, which is treated in a natural way in the present work. Calculations are performed by combining the nucleon dynamics obtained by the antisymmetrized molecular dynamics (AMD) model with a newly developed transport code which we call sJAM. The calculated results for central ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ collisions at 270 MeV/nucleon clearly show that the momentum dependence of the neutron and proton potentials has a significant impact on the $NN\to N\Delta$ process, and this information is strongly reflected in the charged pion ratio (${\pi }^{-}/{\pi }^{+}$). We also investigate the effects of the high-density symmetry energy and the isovector part of the potential of $\Delta$ resonances on pion production, which we find are relatively small compared to the effect of the momentum dependence of the neutron and proton potentials.

   ↳ nucl-thnucl-exPRC(2023)·13 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.