Fri·Oct 27, 2023Friday·October 27, 2023

1. 01*

   Further evidence for shape coexistence in ${}^{79}$Zn${}^m$ near doubly-magic ${}^{78}$Ni

   L. Nies (1 and 2)🇨🇭 · L. Canete (3 and 4)🇫🇮 · D. D. Dao (5)🇫🇷 · S. Giraud (6)🇫🇷 · A. Kankainen (3)🇫🇮 · D. Lunney (7)🇫🇷 · F. Nowacki (5)🇫🇷 · B. Bastin (6)🇫🇷 · M. Stryjczyk (3)🇫🇮 · P. Ascher (8)🇫🇷 · K. Blaum (9)🇩🇪 · R. B. Cakirli (10)🇹🇷 and 22 other authors

   Isomers close to doubly-magic ${}_{28}^{78}$Ni${}_{50}$ provide essential information on the shell evolution and shape coexistence near the $Z=28$ and $N=50$ double shell closure. We report the excitation energy measurement of the $1/2^{+}$ isomer in ${}_{30}^{79}$Zn${}_{49}$ through independent high-precision mass measurements with the JYFLTRAP double Penning trap and with the ISOLTRAP Multi-Reflection Time-of-Flight Mass Spectrometer. We unambiguously place the $1/2^{+}$ isomer at 942(10) keV, slightly below the $5/2^{+}$ state at 983(3) keV. With the use of state-of-the-art shell-model diagonalizations, complemented with Discrete Non Orthogonal shell-model calculations which are used here the first time to interpret shape coexistence, we find low-lying deformed intruder states, similar to other $N=49$ isotones. The $1/2^{+}$ isomer is interpreted as the band-head of a low-lying deformed structure akin to a predicted low-lying deformed band in ${}^{80}$Zn, and points to shape coexistence in ${}^{79,80}$Zn similar to the one observed in ${}^{78}$Ni. The results make a strong case for confirming the claim of shape coexistence in this key region of the nuclear chart.

   nucl-exnucl-thPRL(2023)·15 citations
2. 02*

   Production of $\eta$ and ${\eta }^{\prime }$ mesons in $pp$ and $p$Pb collisions

   LHCb collaboration: R. Aaij · A.S.W. Abdelmotteleb · C. Abellan Beteta · F. Abudinén · T. Ackernley · B. Adeva · M. Adinolfi · P. Adlarson · C. Agapopoulou · C.A. Aidala · Z. Ajaltouni · S. Akar and 1092 other authors

   The production of $\eta$ and ${\eta }^{\prime }$ mesons is studied in proton-proton and proton-lead collisions collected with the LHCb detector. Proton-proton collisions are studied at center-of-mass energies of $5.02$ and $13\mathrm{TeV}$, and proton-lead collisions are studied at a center-of-mass energy per nucleon of $8.16\mathrm{TeV}$. The studies are performed in center-of-mass rapidity regions $2.5<y_{c.m.}<3.5$ (forward rapidity) and $-4.0<y_{c.m.}<-3.0$ (backward rapidity) defined relative to the proton beam direction. The $\eta$ and ${\eta }^{\prime }$ production cross sections are measured differentially as a function of transverse momentum for $1.5<p_{\mathrm{T}}<10\mathrm{GeV}$ and $3<p_{\mathrm{T}}<10\mathrm{GeV}$, respectively. The differential cross sections are used to calculate nuclear modification factors. The nuclear modification factors for $\eta$ and ${\eta }^{\prime }$ mesons agree at both forward and backward rapidity, showing no significant evidence of mass dependence. The differential cross sections of $\eta$ mesons are also used to calculate $\eta /{\pi }^0$ cross section ratios, which show evidence of a deviation from the world average. These studies offer new constraints on mass-dependent nuclear effects in heavy-ion collisions, as well as $\eta$ and ${\eta }^{\prime }$ meson fragmentation.

   nucl-exhep-exPRC(2024)·13 citations
3. 03*

   Baryon density dependence of viscosities of the quark-gluon plasma at hadronization

   Zhidong Yang🇨🇳 · Yifeng Sun🇨🇳 · Lie-Wen Chen🇨🇳

   The $\varphi$ meson and $\Omega$ baryon provide unique probes of the properties of the quark-gluon plasma (QGP) at hadronization in relativistic heavy-ion collisions. Using the quark recombination model with the quark phase-space information parameterized in a viscous blastwave, we perform Bayesian inference of the shear and bulk viscosities of the QGP at hadronization with a temperature of $T\sim 160$ MeV by analyzing the $\varphi$ and $\Omega$ data in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=$ 19.6-200 GeV and Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 2.76 TeV, corresponding to a baryon chemical potential variation from ${\mu }_B\approx 0$ (at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV) to $200$ MeV (at $\sqrt{s_{\mathrm{NN}}}=19.6$ GeV). We find that the shear viscosity to enthalpy ratio $\eta T/(ϵ+P)$ of the QGP at hadronization decreases as ${\mu }_B$ increases, with $\eta T/(ϵ+P)\approx 0.18$ at ${\mu }_B=0$ and $\eta T/(ϵ+P)\approx 0.08$ at ${\mu }_B=200$ MeV, while the corresponding specific bulk viscosity is essentially constant with $\zeta T/(ϵ+P)=0.02\sim 0.04$ for ${\mu }_B<200$ MeV. Our results suggest that the QGP at hadronization ($T\sim 160$ MeV) with finite baryon density is more close to perfect fluid than that with zero baryon density.

   ↳ nucl-thastro-ph.HEhep-phnucl-exPRC(2024)·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.