Fri·Jun 10, 2022Friday·June 10, 2022

1. 01*

   The impact of ${}^{17}$O$+\alpha$ reaction rate uncertainties on the s-process in rotating massive stars

   J. Frost-Schenk · P. Adsley🇿🇦 · A.M. Laird🇬🇧 · R. Longland🇺🇸 · C. Angus🇩🇰 · C. Barton🇬🇧 · A. Choplin🇧🇪 · C. Aa. Diget · R. Hirschi🇬🇧 · C. Marshall🇺🇸 · F. Portillo Chaves · K. Setoodehnia🇺🇸

   Massive stars are crucial to galactic chemical evolution for elements heavier than iron. Their contribution at early times in the evolution of the Universe, however, is unclear due to poorly constrained nuclear reaction rates. The competing ${}^{17}$O($\alpha ,\gamma$)${}^{21}$Ne and ${}^{17}$O($\alpha ,n$)${}^{20}$Ne reactions strongly impact weak s-process yields from rotating massive stars at low metallicities. Abundant ${}^{16}$O absorbs neutrons, removing flux from the s-process, and producing ${}^{17}$O. The ${}^{17}$O($\alpha ,n$)${}^{20}$Ne reaction releases neutrons, allowing continued s-process nucleosynthesis, if the ${}^{17}$O($\alpha ,\gamma$)${}^{21}$Ne reaction is sufficiently weak. While published rates are available, they are based on limited indirect experimental data for the relevant temperatures and, more importantly, no uncertainties are provided. The available nuclear physics has been evaluated, and combined with data from a new study of astrophysically relevant ${}^{21}$Ne states using the ${}^{20}$Ne($d,p$)${}^{21}$Ne reaction. Constraints are placed on the ratio of the ($\alpha ,n$)/($\alpha ,\gamma$) reaction rates with uncertainties on the rates provided for the first time. The new rates favour the ($\alpha ,n$) reaction and suggest that the weak s-process in rotating low-metallicity stars is likely to continue up to barium and, within the computed uncertainties, even to lead.

   nucl-exastro-ph.SRnucl-thMNRAS(2022)·8 citations
2. 02*

   Observation of flow angle and flow magnitude fluctuations in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV at the CERN Large Hadron Collider

   ALICE Collaboration

   This Letter reports on the first measurements of transverse momentum dependent flow angle ${\Psi }_n$ and flow magnitude $v_n$ fluctuations, determined using new four-particle correlators. The measurements are performed for various centralities in Pb-Pb collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV with ALICE at the CERN Large Hadron Collider. Both flow angle and flow magnitude fluctuations are observed in the presented centrality ranges and are strongest in the most central collisions and for a transverse momentum $p_{\mathrm{T}}>2$ GeV/$c$. Comparison with theoretical models, including iEBE-VISHNU, MUSIC, and AMPT, show that the measurements exhibit unique sensitivities to the initial state of heavy-ion collisions.

   nucl-exhep-exPRC(2023)·21 citations
3. 03*

   Anisotropic flow and flow fluctuations of identified hadrons in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

   ALICE Collaboration

   The first measurements of elliptic flow of ${\pi }^{\pm }$, ${\mathrm{K}}^{\pm }$, p+$\overline{\mathrm{p}}$, ${\mathrm{K}}_{\mathrm{S}}^0$, $\Lambda$+$\overline{\Lambda }$, $\varphi$, ${\Xi }^{-}$+${\Xi }^{+}$, and ${\Omega }^{-}$+${\Omega }^{+}$ using multiparticle cumulants in Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV are presented. Results obtained with two- ($v_2\{2\}$) and four-particle cumulants ($v_2\{4\}$) are shown as a function of transverse momentum, $p_{\mathrm{T}}$, for various collision centrality intervals. Combining the data for both $v_2\{2\}$ and $v_2\{4\}$ also allows us to report the first measurements of the mean elliptic flow, elliptic flow fluctuations, and relative elliptic flow fluctuations for various hadron species. These observables probe the event-by-event eccentricity fluctuations in the initial state and the contributions from the dynamic evolution of the expanding quark-gluon plasma. The characteristic features observed in previous $p_{\mathrm{T}}$-differential anisotropic flow measurements for identified hadrons with two-particle correlations, namely the mass ordering at low $p_{\mathrm{T}}$ and the approximate scaling with the number of constituent quarks at intermediate $p_{\mathrm{T}}$, are similarly present in the four-particle correlations and the combinations of $v_2\{2\}$ and $v_2\{4\}$. In addition, a particle species dependence of flow fluctuations is observed that could indicate a significant contribution from final state hadronic interactions. The comparison between experimental measurements and CoLBT model calculations, which combine the various physics processes of hydrodynamics, quark coalescence, and jet fragmentation, illustrates their importance over a wide $p_{\mathrm{T}}$ range.

   nucl-exhep-exJHEP(2023)·54 citations
4. 04*

   Theoretical Uncertainty Quantification for Heavy-ion Fusion

   K. Godbey🇺🇸 · A.S. Umar🇺🇸 · C. Simenel🇦🇺

   Despite recent advances and focus on rigorous uncertainty quantification for microscopic models of quantum many-body systems, the uncertainty on the dynamics of those systems has been under-explored. To address this, we have used time-dependent Hartree-Fock to examine the model uncertainty for a collection of low-energy, heavy-ion fusion reactions. Fusion reactions at near-barrier energies represent a rich test-bed for the dynamics of quantum many-body systems owing to the complex interplay of collective excitation, transfer, and static effects that determine the fusion probability of a given system. While the model uncertainty is sizable for many of the systems studied, the primary contribution comes from ill-constrained static properties, such as the neutron radius of neutron-rich nuclei. These large uncertainties motivate the use of information from reactions to better constrain existing models and to infer static properties from reaction data.

   ↳ nucl-thnucl-exPRC(2022)·24 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.