Fri·Nov 24, 2023Friday·November 24, 2023

1. 01*

   Fission of 215Fr studied with gamma spectroscopic methods

   K. Miernik🇵🇱 · A. Korgul🇵🇱 · W. Poklepa🇵🇱 · J. N. Wilson🇫🇷 · G. Charles🇫🇷 · S. Czajkowski🇫🇷 · P. Czyż🇵🇱 · A. Fijałkowska🇵🇱 · L. M. Fraile🇪🇸 · P. Garczyński🇵🇱 · K. Hauschild🇫🇷 · C. Hiver🇫🇷 and 14 other authors

   Background: Asymmetric fission is known to occur in two regions, the actinides and sub-lead, and is dependent on the fissioning system excitation energy. Experimental evidence in the sub-lead region show that this mode is surprisingly persistent with increasing energy and its origin is not fully understood. Purpose: To experimentally study the fusion-fission reaction of ${}^{215}$Fr at moderate excitation energy and determine previously unknown independent fission yields and other properties. Method: The compound nucleus was formed in the reaction ${}^{18}$O + ${}^{197}$Au. The prompt gamma-rays emitted during the reaction were measured with the high efficiency and high granularity $\nu$-ball2 spectrometer. Independent fission yields of even-even nuclei were determined by detecting triple-gamma cascades in the fission fragments. Results: The observed yields, although dominated by a symmetric peak, show maxima for heavy fragment of $Z\approx 54-56$, which is consistent with the known results in the actinide region but unexpected for the nuclide of interest, and at the studied excitation energy. Conclusions: The mode of asymmetric fission is present even at relatively high excitation energies in the system studied. This observation matches experimental findings in the sub-lead region, contrary to the actinides, and so far there is no well-developed explanation of this phenomenon.

   nucl-exPRC(2023)·6 citations
2. 02*

   Spin dynamics in intermediate-energy heavy-ion collisions with rigorous angular momentum conservation

   Rong-Jun Liu🇨🇳 · Jun Xu🇨🇳

   We have revisited the spin dynamics in intermediate-energy heavy-ion collisions based on the improved spin- and isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model, particularly with the constraint of rigorous angular momentum conservation incorporated. We have studied the spin polarization of free nucleons and tritons/${}^3$He as well as the spin alignment of deuterons, and predicted the flow splittings for their different spin states. We have also demonstrated that the spin-dependent potential may enhance dissipations and thus have a non-negligible effect on the spin-averaged transverse flow at low collision energies. When rigorous angular momentum conservation in each spin-dependent nucleon-nucleon collision is incorporated, it affects the overall dynamics, the flow, and also the spin polarization, while the effects of the spin-orbit potential on the spin-related observables are still appreciable. The well-developed SIBUU model could be further extended to include hyperons or vector mesons, or used as a hadronic afterburner for spin-related studies in relativistic heavy-ion collisions, with more inelastic channels incorporated in the future.

   ↳ nucl-thhep-exnucl-exPRC(2024)·11 citations
3. 03*

   Enhanced Dilepton production near the color superconducting phase and the QCD critical point

   Toru Nishimura🇯🇵 · Yasushi Nara🇯🇵 · Jan Steinheimer🇩🇪

   The dilepton production yields in relativistic heavy ion collisions are investigated along isentropic trajectories in the quark (Wigner) phase within the two-flavor Nambu-Jona-Lasinio model. An enhancement of the ultra-low energy dilepton yield in the vicinity of the color superconducting (CSC) phase and the QCD critical point (QCD-CP) is found, compared to the free quark gas. Furthermore, we have found a nontrivial structure in the beam energy dependence of the ultra-low energy dilepton yield. A local maximum and minimum of the dilepton yield as a function of entropy per baryon emerge when the trajectories are close to both locations of the CSC phase transition line and the QCD-CP. Only the maximum appears in the scenario without the CSC phase but with the QCD-CP. On the other hand, when only the CSC phase is considered, the dilepton yield monotonically increases as the beam energy decreases. These distinctive patterns could potentially serve as signals of the CSC phase and QCD-CP. In addition, it is found that the dilepton production yield and the location of the minimum strongly depend on the value of diquark coupling, suggesting the possibility that the value of the diquark coupling may be extracted from experimental data.

   ↳ hep-phnucl-exnucl-thEPJA(2024)·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.