Wed·Aug 11, 2021Wednesday·August 11, 2021

1. 01*

   Quarkonia as probes of the QGP and the initial stages of the heavy-ion collisions with ALICE

   Ingrid McKibben Lofnes (for the ALICE Collaboration)🇳🇴

   Studies of quarkonium production in heavy-ion collisions can be used for probing QGP properties. The suppression and regeneration of bound quarkonium states is sensitive to the medium properties. Modifications of the quarkonium polarization in Pb-Pb collisions with respect to pp collisions may give further insight into the suppression and regeneration mechanisms in the QGP. Quarkonia are also sensitive to the initial stages of heavy-ion collisions, and measurements in photonuclear collisions may help constrain the nuclear gluon-distribution at low Bjorken-$x$. In this work, recent quarkonium measurements performed by ALICE in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV will be discussed. Preliminary measurements of the inclusive J/$\psi$ $R_{\mathrm{AA}}$ measured at both forward and midrapidity will be presented. The J/$\psi$ polarization measured for the first time in Pb-Pb collisions, as well as preliminary measurements of the coherent J/$\psi$ photoproduction cross section, will be discussed.

   nucl-exhep-exEPJ Web Conf.(2022)·5 citations
2. 02*

   Advancement of Photospheric Radius Expansion and Clocked Type-I X-Ray Burst Models with the New ${}^{22}$Mg$(\alpha ,p{)}^{25}$Al Reaction Rate Determined at Gamow Energy

   J. Hu · H. Yamaguchi · Y. H. Lam🇨🇳 · A. Heger🇦🇺 · D. Kahl · A. M. Jacobs · Z. Johnston🇺🇸 · S. W. Xu🇨🇳 · N. T. Zhang🇨🇳 · S. B. Ma🇨🇳 · L. H. Ru · E. Q. Liu and 25 other authors

   We report the first (in)elastic scattering measurement of ${}^{25}\mathrm{Al}+p$ with the capability to select and measure in a broad energy range the proton resonances in ${}^{26}$Si contributing to the ${}^{22}$Mg$(\alpha ,p)$ reaction at type I x-ray burst energies. We measured spin-parities of four resonances above the $\alpha$ threshold of ${}^{26}$Si that are found to strongly impact the ${}^{22}$Mg$(\alpha ,p)$ rate. The new rate advances a state-of-the-art model to remarkably reproduce light curves of the GS 1826$-$24 clocked burster with mean deviation $<9$ % and permits us to discover a strong correlation between the He abundance in the accreting envelope of photospheric radius expansion burster and the dominance of ${}^{22}$Mg$(\alpha ,p)$ branch.

   nucl-exastro-ph.HEnucl-thPRL(2021)·22 citations
3. 03*

   Holographic charm and bottom pentaquarks I: Mass spectra with spin effects

   Yizhuang Liu🇵🇱 · Maciej A. Nowak🇵🇱 · Ismail Zahed🇺🇸

   We revisit the three non-strange pentaquarks $[\frac{1}{2}{\frac{1}{2}}^{-}{]}_{S=0,1}$ and $[\frac{1}{2}{\frac{3}{2}}^{-}{]}_{S=1}$ predicted using the holographic dual description, where chiral and heavy quark symmetry are manifest in the triple limit of a large number of colors, large quark mass and strong ${}^{\prime }$t Hooft gauge coupling. In the heavy quark limit, the pentaquarks with internal heavy quark spin $S$ are all degenerate. The holographic pentaquarks are dual to an instanton bound to heavy mesons in bulk, without the shortcomings related to the nature of the interaction and the choice of the hard core inherent to the molecular constructions. We explicitly derive the spin-spin and spin-orbit couplings arising from next to leading order in the heavy quark mass, and lift totally the internal spin degeneray, in fair agreement with the newly reported charmed pentaquarks from LHCb. New charm and bottom pentaquark states are predicted.

   ↳ hep-phhep-thnucl-exnucl-thPRD(2021)·13 citations
4. 04*

   Angular momentum removal by neutron and $\gamma$-ray emissions during fission fragment decays

   I. Stetcu🇺🇸 · A.E. Lovell🇺🇸 · P. Talou🇺🇸 · T. Kawano🇺🇸 · S. Marin🇺🇸 · S.A. Pozzi🇮🇹 · A. Bulgac🇺🇸

   We investigate the angular momentum removal from fission fragments (FFs) through neutron and $\gamma$-ray emission, where we find that about half the neutrons are emitted with angular momenta $\ge 1.5\hslash$ and that the change in angular momentum after the emission of neutrons and statistical $\gamma$ rays is significant, contradicting usual assumptions. Per fission event, in our simulations, the neutron and statistical $\gamma$-ray emissions change the spin of the fragment by 3.5 -- 5~$\hslash$, with a large standard deviation comparable to the average value. Such wide angular momentum removal distributions can hide any underlying correlations in the fission fragment initial spin values. Within our model, we reproduce data on spin measurements from discrete transitions after neutron emissions, especially in the case of light FFs. The agreement further improves for the heavy fragments if one removes from the analysis the events that would produce isomeric states. Finally, we show that while in our model the initial FF spins do not follow a saw-tooth like behavior observed in recent measurements, the average FF spin computed after neutron and statistical $\gamma$ emissions exhibits a shape that resembles a saw tooth. This suggests that the average FF spin measured after statistical emissions is not necessarily connected with the scission mechanism as previously implied.

   ↳ nucl-thnucl-exPRL(2021)·45 citations
5. 05*

   Single-Logarithmic Corrections to Small-$x$ Helicity Evolution

   Yossathorn Tawabutr🇺🇸

   The small-$x$ quark helicity evolution equations at double-logarithmic order, with the kernel $\sim {\alpha }_s{\ln }^2(1/x)$, have been derived previously. In this work, we derive the single-logarithmic corrections to the equations, to order ${\alpha }_s\ln (1/x)$ of the evolution kernel. The new equations include the effects of the running coupling and the unpolarized small-$x$ evolution, both of which are parametrically significant at single-logarithmic order. The large-$N_c$ and large-$N_c\&N_f$ approximations to the equation are computed. (Here, $N_c$ and $N_f$ are the numbers of quark colors and flavors, respectively.) Their solutions will provide more precise estimates of the quark helicity distribution at small $x$, contributing to the resolution of the proton spin puzzle.

   ↳ hep-phhep-exnucl-exnucl-thSciPost Phys.Proc.(2022)·4 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.