Thu·Jul 9, 2020Thursday·July 9, 2020

1. 01*

   Charged-particle branching ratios above the neutron threshold in ${}^{19}$F: constraining ${}^{15}$N production in core-collapse supernovae

   P. Adsley · F. Hammache · N. de Séréville · V. Alcindor · M. Assi é · D. Beaumel M.Chabot · M. Degerlier · C. Delafosse · T. Faestermann · F. Flavigny · S. P. Fox · R. Garg and 21 other authors

   Spatially-correlated overabundances of ${}^{15}$N and ${}^{18}$O observed in some low-density graphite meteoritic grains have been connected to nucleosynthesis taking place in the helium-burning shell during core-collapse supernovae. Two of the reactions which have been identified as important to the final abundances of ${}^{15}$N and ${}^{18}$O are ${}^{18}$F($n,\alpha$)${}^{15}$N and ${}^{18}$F($n,p$)${}^{18}$O. The relative strengths of the ${}^{18}$F($n,\alpha$)${}^{15}$N and ${}^{18}$F($n,p$)${}^{18}$O reactions depend on the relative ${\alpha }_0$ and $p_0$ decays from states above the neutron threshold in ${}^{19}$F in addition to other properties. Experimental data on the charged-particle decays from these highly excited states are lacking or inconsistent. Two experiments were performed using proton inelastic scattering from LiF targets and magnetic spectrographs. The first experiment used the high-resolution Q3D spectrograph at Munich to constrain properties of levels in ${}^{19}$F. A second experiment using the Orsay Split-Pole spectrograph and an array of silicon detectors was performed in order to measure the charged-particle decays of neutron-unbound levels in ${}^{19}$F. A number of levels in ${}^{19}$F have been identified along with their corresponding charged-particle decays. The first state above the neutron threshold which has an observed proton-decay branch to the ground state of ${}^{18}$O lies 68 keV above the neutron threshold while the $\alpha$-particle decays from the neutron-unbound levels are generally observed to be much stronger than the proton decays. Neutron-unbound levels in ${}^{19}$F are observed to decay predominantly by $\alpha$-particle emission, supporting the role of ${}^{18}$F($n,\alpha$)${}^{15}$N in the production of ${}^{15}$N in the helium-burning shell of supernovae. Improved resonant-scattering reaction data are required in order to be able to determine the reaction rates accurately.

   nucl-exastro-ph.SRPRC(2021)·1 citation
2. 02*

   $\Lambda$ and $\Sigma$ Excitations and the Quark Model

   E. Klempt🇩🇪 · V. Burkert🇺🇸 · U. Thoma🇩🇪 · L. Tiator🇩🇪 · R. Workman🇺🇸

   The spectrum of $\Lambda$ and $\Sigma$ excitations is reviewed taking into account (nearly) all hyperon resonances which were seen in early analyses or in one of the recent partial-wave analyses. The spectrum is compared with the old Isgur-Karl model and the Bonn model. These models allows us to discuss the SU(3) structure of the observed resonances. The SU(3) decomposition is compared with SU(6) relations between the different decay modes. Seven $\Lambda$ states are proposed to be classified as SU(3) singlet states. The hyperon spectrum is compared with the spectrum of $N$ and $\Delta$ resonances.

   nucl-exEPJA(2020)·15 citations
3. 03*

   GW190814: Impact of a 2.6 solar mass neutron star on nucleonic equations of state

   F.J. Fattoyev🇺🇸 · C.J. Horowitz🇺🇸 · J. Piekarewicz🇺🇸 · Brendan Reed🇺🇸

   Is the secondary component of GW190814 the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system [R. Abbott et al., ApJ Lett., 896, L44 (2020)]? This is the central question animating this letter. Covariant density functional theory provides a unique framework to investigate both the properties of finite nuclei and neutron stars, while enforcing causality at all densities. By tuning existing energy density functionals we were able to: (a) account for a 2.6 Msun neutron star, (b) satisfy the original constraint on the tidal deformability of a 1.4 Msun neutron star, and (c) reproduce ground-state properties of finite nuclei. Yet, for the class of models explored in this work, we find that the stiffening of the equation of state required to support super-massive neutron stars is inconsistent with either constraints obtained from energetic heavy-ion collisions or from the low deformability of medium-mass stars. Thus, we speculate that the maximum neutron star mass can not be significantly higher than the existing observational limit and that the 2.6 Msun compact object is likely to be the lightest black hole ever discovered.

   ↳ nucl-thastro-ph.HEnucl-exPRC(2020)·236 citations
4. 04*

   Cumulants of multiple conserved charges and global conservation laws

   Volodymyr Vovchenko🇺🇸 · Roman V. Poberezhnyuk🇺🇦 · Volker Koch🇺🇸

   We analyze the behavior of cumulants of conserved charges in a subvolume of a thermal system with exact global conservation laws by extending a recently developed subensemble acceptance method (SAM) [V. Vovchenko et al., arXiv:2003.13905] to multiple conserved charges. Explicit expressions for all diagonal and off-diagonal cumulants up to sixth order that relate them to the grand canonical susceptibilities are obtained. The derivation is presented for an arbitrary equation of state with an arbitrary number of different conserved charges. The global conservation effects cancel out in any ratio of two second order cumulants, in any ratio of two third order cumulants, as well as in a ratio of strongly intensive measures $\Sigma$ and $\Delta$ involving any two conserved charges, making all these quantities particularly suitable for theory-to-experiment comparisons in heavy-ion collisions. We also show that the same cancellation occurs in correlators of a conserved charge, like the electric charge, with any non-conserved quantity such as net proton or net kaon number. The main results of the SAM are illustrated in the framework of the hadron resonance gas model. We also elucidate how net-proton and net-$\Lambda$ fluctuations are affected by conservation of electric charge and strangeness in addition to baryon number.

   ↳ hep-phnucl-exnucl-thJHEP(2020)·53 citations
5. 05*

   Deciphering QCD dynamics in small collision systems using event shape and final state multiplicity at the Large Hadron Collider

   Suman Deb🇮🇳 · Sushanta Tripathy🇮🇳 · Golam Sarwar🇮🇳 · Raghunath Sahoo🇮🇳 · Jan-e Alam🇮🇳

   The high-multiplicity pp collisions at the Large Hadron Collider energies with various heavy-ion-like signatures have warranted a deeper understanding of the underlying physics and particle production mechanisms. It is a common practice to use experimental data on the hadronic transverse momentum ($p_T$) spectra to extract thermodynamical properties of the system formed in heavy ion and high multiplicity pp collisions. The non-availability of event topology dependent experimental data for pp collisions at $\sqrt{s}$ = 13 TeV on the spectra of non-strange and strange hadrons constrains us to use the PYTHIA8 simulated numbers to extract temperature-like parameters to study the event shape and multiplicity dependence of specific heat capacity, conformal symmetry breaking measure (CSBM) and speed of sound. The observables show a clear dependence on event multiplicity and event topology. Thermodynamics of the system is largely governed by the light particles because of their relatively larger abundances. In this regards, a threshold in the particle production, ${\mathrm{N}}_{\mathrm{ch}}\simeq$ (10-20) in the final state multiplicity emerges out from the present study, confirming some of the earlier findings in this direction. As for heavier hadrons with relatively small abundances, a similar threshold is observed for $⟨{\mathrm{N}}_{\mathrm{ch}}⟩\simeq$ 40 hinting towards formation of a thermal bath where all the heavier hadrons are in equilibrium.

   ↳ hep-phhep-exnucl-exnucl-thEPJA(2020)·12 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.