Thu·Nov 23, 2023Thursday·November 23, 2023

1. 01*

   Validation of the ${}^{10}\mathrm{Be}$ Ground-State Molecular Structure Using ${}^{10}\mathrm{Be}(p,p\alpha {)}^6\mathrm{He}$ Triple Differential Reaction Cross-Section Measurements

   P. J. Li🇨🇳 · D. Beaumel🇫🇷 · J. Lee🇨🇳 · M. Assié🇫🇷 · S. Chen🇨🇳 · S. Franchoo🇫🇷 · J. Gibelin🇫🇷 · F. Hammache🇫🇷 · T. Harada🇯🇵 · Y. Kanada-En'yo🇯🇵 · Y. Kubota🇯🇵 · S. Leblond🇨🇳 and 49 other authors

   The cluster structure of the neutron-rich isotope ${}^{10}$Be has been probed via the $(p,p\alpha )$ reaction at 150 MeV/nucleon in inverse kinematics and in quasifree conditions. The populated states of ${}^6$He residues were investigated through missing mass spectroscopy. The triple differential cross-section for the ground-state transition was extracted for quasifree angle pairs (${\theta }_p$, ${\theta }_{\alpha }$) and compared to distorted-wave impulse approximation reaction calculations performed in a microscopic framework using successively the Tohsaki-Horiuchi-Schuck-Röpke product wave-function and the wave-function deduced from Antisymmetrized Molecular Dynamics calculations. The remarkable agreement between calculated and measured cross-sections in both shape and magnitude validates the molecular structure description of the ${}^{10}$Be ground-state, configured as an $\alpha$-$\alpha$ core with two valence neutrons occupying $\pi$-type molecular orbitals.

   nucl-exnucl-thPRL(2023)·40 citations
2. 02*

   Measurements of chemical potentials in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV

   ALICE Collaboration

   This Letter presents the most precise measurement to date of the matter-antimatter imbalance at midrapidity in Pb-Pb collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. Using the Statistical Hadronization framework, it is possible to obtain the value of the electric charge and baryon chemical potentials, ${\mu }_Q=-0.18\pm 0.90$ MeV and ${\mu }_B=0.71\pm 0.45$ MeV, with unprecedented precision. A centrality-differential study of the antiparticle-to-particle yield ratios of charged pions, protons, $\Omega$-baryons, and light (hyper)nuclei is performed. These results indicate that the system created in Pb-Pb collisions at the LHC is on average baryon-free and electrically neutral at midrapidity.

   nucl-exhep-exPRL(2024)·32 citations
3. 03*

   Exclusive $J/\psi$, $\psi (2s)$, and $e^{+}{e}^{-}$ pair production in Au$+$Au ultra-peripheral collisions at RHIC

   STAR Collaboration

   Measurements of exclusive $J/\psi$, $\psi (2s)$, and electron-positron ($e^{+}{e}^{-}$) pair photoproduction in Au$+$Au ultra-peripheral collisions are reported by the STAR experiment at $\sqrt{s_{{}_{\mathrm{NN}}}}=200\mathrm{GeV}$. We report several first measurements at the Relativistic Heavy-Ion Collider, which are i) $J/\psi$ photoproduction with large momentum transfer up to $2.2(GeV/c{)}^2$, ii) coherent $J/\psi$ photoproduction associated with neutron emissions from nuclear breakup, iii) the rapidity dependence of incoherent $J/\psi$ photoproduction, iv) the $\psi (2s)$ photoproduction cross section at mid-rapidity, and v) $e^{+}{e}^{-}$ pair photoproduction up to high invariant mass of 6 $GeV/{\mathrm{c}}^2$. For measurement ii), the coherent $J/\psi$ total cross section of ${\gamma }^{\ast }+\mathrm{Au}\to J/\psi +\mathrm{Au}$ as a function of the center-of-mass energy $W_{\gamma \ast \mathrm{N}}$ has been obtained without photon energy ambiguities. The data are quantitatively compared with the Monte Carlo models STARlight, Sartre, BeAGLE, and theoretical calculations of gluon saturation with color glass condensate, nuclear shadowing with leading twist approximation, Quantum Electrodynamics, and the Next-to-Leading Order perturbative QCD. At the photon-nucleon center-of-mass energy of 25.0 GeV, the coherent and incoherent $J/\psi$ cross sections of Au nuclei are found to be $71\pm 10\%$ and $36\pm 7\%$, respectively, of that of free protons. These data provide an important experimental constraint for nuclear parton distribution functions and a unique opportunity to advance the understanding of the nuclear modification effect at the top RHIC energy.

   nucl-exhep-exhep-phnucl-thPRC(2024)·40 citations
4. 04*

   Observation of strong nuclear suppression in exclusive $J/\psi$ photoproduction in Au$+$Au ultra-peripheral collisions at RHIC

   STAR Collaboration

   We report a measurement of exclusive $J/\psi$ photoproduction in Au$+$Au ultra-peripheral collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}=200$ GeV using the STAR detector. For the first time, i) the rapidity correlation between $J/\psi$ photoproduction and neutron emission from nuclear breakups has been experimentally measured; ii) nuclear suppression factors are measured for both the coherent and incoherent $J/\psi$ production. At photon-nucleon center-of-mass energy of 25.0 GeV, the coherent and incoherent $J/\psi$ cross sections of Au nuclei are found to be $71\pm 10\%$ and $36\pm 7\%$, respectively, of that of free protons. The stronger suppression observed in the incoherent production provides a new experimental handle to study the initial-state parton density in heavy nuclei. Data are compared with theoretical models quantitatively.

   nucl-exhep-exhep-phnucl-thPRL(2024)·39 citations
5. 05*

   Strong Gravity Extruding Peaks in Speed of Sound Profiles of Massive Neutron Stars

   Bao-Jun Cai🇨🇳 · Bao-An Li🇺🇸

   The speed of sound squared (SSS) $s^2$ in massive neutron stars (NSs) characterizes not only the stiffness of supradense neutron-rich matter within but also equivalently properties of the curved geometry due to the strong-field gravity and matter-geometry coupling. A peaked density or radius profile of $s^2$ has been predicted for massive NSs using various NS Equation of State (EOS) models. However, the nature, cause, location and size of the peak in $s^2$ profiles are still very EOS model dependent. In this work, we investigate systematically $s^2$ profiles in massive NSs in a new approach that is independent of the nuclear EOS model and without any presumption about the NS structure and/or composition. In terms of the small quantities (reduced radius, the energy density and pressure scaled by their central values), we perform double-element perturbative expansions in solving perturbatively the scaled Tolman--Oppenheimer--Volkoff (TOV) equations and analyzing $s^2$ profiles from the Newtonian limit to the general relativistic (GR) case. The GR term in the TOV equations plays a twofold role: it compresses NS matter and modifies the pressure/energy density ratio from small values in Newtonian stars showing no $s^2$ peak to large ones for massive NSs possessing a peak in their $s^2$ profiles, and eventually takes away the peak in extremely compact/massive NSs approaching the causality limit. {In particular, the peaked behavior in $s^2$ is expected to emerge near the center of massive NSs like PSR J0740+6620, while a sharp phase transition is unlikely to occur there.} These features revealed from our analyses are universal as they are intrinsic properties of the GR stellar structure equations independent of the still very uncertain EOS of supradense neutron-rich matter in NSs.

   ↳ nucl-thastro-ph.HEastro-ph.SRgr-qc+1PRD(2024)·13 citations
6. 06*

   Multiplicity dependence of charged-particle intra-jet properties in pp collisions at $\sqrt{s}$ = 13 TeV

   ALICE Collaboration

   The first measurement of the multiplicity dependence of intra-jet properties of leading charged-particle jets in proton-proton (pp) collisions is reported. The mean charged-particle multiplicity and jet fragmentation distributions are measured in minimum-bias and high-multiplicity pp collisions at $\sqrt{s}$ = 13 TeV using the ALICE detector. Jets are reconstructed from charged particles produced in the midrapidity region ($|\eta |<0.9$) using the sequential recombination anti-$k_{\mathrm{T}}$ algorithm with jet resolution parameters $R=0.2$, 0.3, and 0.4 for the transverse momentum ($p_{\mathrm{T}}$) interval 5-110 GeV/$c$. High-multiplicity events are selected by the forward V0 scintillator detectors. The mean charged-particle multiplicity inside the leading jet cone rises monotonically with increasing jet $p_{\mathrm{T}}$ in qualitative agreement with previous measurements at lower energies. The distributions of jet fragmentation function variables $z^{\mathrm{ch}}$ and ${\xi }^{\mathrm{ch}}$ are measured for different jet-$p_{\mathrm{T}}$ intervals. Jet-$p_{\mathrm{T}}$ independent fragmentation of leading jets is observed for wider jets except at high- and low-$z^{\mathrm{ch}}$. The observed hump-backed plateau structure in the ${\xi }^{\mathrm{ch}}$ distribution indicates suppression of low-$p_{\mathrm{T}}$ particles. In high-multiplicity events, an enhancement of the fragmentation probability of low-$z^{\mathrm{ch}}$ particles accompanied by a suppression of high-$z^{\mathrm{ch}}$ particles is observed compared to minimum-bias events. This behavior becomes more prominent for low-$p_{\mathrm{T}}$ jets with larger jet radius. The results are compared with predictions of QCD-inspired event generators, PYTHIA 8 with Monash 2013 tune and EPOS LHC. It is found that PYTHIA 8 qualitatively reproduces the jet modification in high-multiplicity events except at high jet $p_{\mathrm{T}}$. These measurements provide important constraints to models of jet fragmentation.

   ↳ hep-exnucl-exEPJC(2024)·13 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.