Nuclear Theory·nucl-th

Monday·November 27, 2023

21 papers—8 primary·13 cross-listed

09
Exclusive $J / ψ$ , $ψ (2 s)$ , and $e^{+} e^{-}$ pair production in Au $+$ Au ultra-peripheral collisions at RHIC
STAR Collaboration
Measurements of exclusive $J / ψ$ , $ψ (2 s)$ , and electron-positron ( $e^{+} e^{-}$ ) pair photoproduction in Au $+$ Au ultra-peripheral collisions are reported by the STAR experiment at $s_{_{NN}} = 200 GeV$ . We report several first measurements at the Relativistic Heavy-Ion Collider, which are i) $J / ψ$ photoproduction with large momentum transfer up to $2.2 (GeV/c)^{2}$ , ii) coherent $J / ψ$ photoproduction associated with neutron emissions from nuclear breakup, iii) the rapidity dependence of incoherent $J / ψ$ photoproduction, iv) the $ψ (2 s)$ photoproduction cross section at mid-rapidity, and v) $e^{+} e^{-}$ pair photoproduction up to high invariant mass of 6 $GeV/ c^{2}$ . For measurement ii), the coherent $J / ψ$ total cross section of $γ^{*} + Au \to J/ ψ + Au$ as a function of the center-of-mass energy $W_{γ * N}$ 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 $J / ψ$ 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)·39 citations
10
Observation of strong nuclear suppression in exclusive $J / ψ$ photoproduction in Au $+$ Au ultra-peripheral collisions at RHIC
STAR Collaboration
We report a measurement of exclusive $J / ψ$ photoproduction in Au $+$ Au ultra-peripheral collisions at $s_{_{NN}} = 200$ GeV using the STAR detector. For the first time, i) the rapidity correlation between $J / ψ$ photoproduction and neutron emission from nuclear breakups has been experimentally measured; ii) nuclear suppression factors are measured for both the coherent and incoherent $J / ψ$ production. At photon-nucleon center-of-mass energy of 25.0 GeV, the coherent and incoherent $J / ψ$ 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)·38 citations
11
Probing Dark Sectors with Neutron Stars
Susan Gardner🇺🇸 · Mohammadreza Zakeri🇺🇸
Tensions in the measurements of neutron and kaon weak decays, such as of the neutron lifetime, may speak to the existence of new particles and dynamics not present in the Standard Model (SM). In scenarios with dark sectors, particles that couple feebly to those of the SM appear. We offer a focused overview of such possibilities and describe how the observations of neutron stars, which probe either their structure or dynamics, limit them. In realizing these constraints, we highlight how the assessment of particle processes within dense baryonic matter impacts the emerging picture -- and we emphasize both the flavor structure of the constraints and their broader connections to cogenesis models of dark matter and baryogenesis.
↳ hep-phastro-ph.HEnucl-thUniverse(2024)·18 citations
12
Mass and radius of the most massive neutron star: The probe of the equation of state and perturbative QCD
Shao-Peng Tang🇨🇳 · Ming-Zhe Han🇨🇳 · Yong-Jia Huang🇨🇳 · Yi-Zhong Fan🇨🇳 · Da-Ming Wei🇨🇳
Recently, an association of GW190425 and FRB 20190425A had been claimed and a highly magnetized neutron star (NS) remnant was speculated. Given the $\sim 2.5$ -h delay of the occurrence of FRB 20190425A, a uniformly rotating supramassive magnetar is favored since the differential rotation would have been promptly terminated by the magnetic braking. The required maximum gravitational mass ( $M_{TOV}$ ) of the nonrotating NS is $\approx 2.77 M_{⊙}$ , which is strongly in tension with the relatively low $M_{TOV} \approx 2.25 M_{⊙}$ obtained in current equation of state (EOS) constraints incorporating perturbative quantum chromodynamics (pQCD) information. However, the current mass-radius and mass-tidal deformability measurements of NSs alone do not convincingly exclude the high $M_{TOV}$ possibility. By performing EOS constraints with mock measurements, we find that with a $2%$ determination for the radius of PSR J0740+6620-like NS it is possible to distinguish between the low and high $M_{TOV}$ scenarios. We further explore the prospect to resolve the issue of the appropriate density to impose the pQCD constraints with future massive NS observations or determinations of $M_{TOV}$ and/or $R_{TOV}$ . It turns out that measuring the radius of a PSR J0740+6620-like NS is insufficient to probe the EOSs around 5 nuclear saturation density, where the information from pQCD becomes relevant. The additional precise $M_{TOV}$ measurements anyhow could provide insights into the EOS at such a density. Indeed, supposing the central engine of GRB 170817A is a black hole formed via the collapse of a supramassive NS, the resulting $M_{TOV} \approx 2.2 M_{⊙}$ considerably softens the EOS at the center of the most massive NS, which is in favor of imposing the pQCD constraint at density beyond the one achievable in the NSs.
↳ astro-ph.HEgr-qcnucl-thPRD(2024)·8 citations
13
Bose-Einstein condensate stars in combined Rastall-Rainbow gravity
O. P. Jyothilakshmi🇮🇳 · Lakshmi J. Naik🇮🇳 · V. Sreekanth🇮🇳
We study zero and finite temperature static Bose-Einstein condensate (BEC) stars in the combined Rastall-Rainbow (RR) theory of gravity by considering different BEC equation of states (EoSs). We obtain the global properties of BEC stars by solving the modified Tolman-Oppenheimer-Volkoff equations with values of Rastall parameter $κ$ and Rainbow function $Σ$ chosen accordingly to get the results in theories of Rastall, Rainbow and RR. We observe that the parameter $κ$ has negligible effect on the maximum mass of the stars considered, whereas $Σ$ alters it significantly, and increasing the value of $κ$ beyond a certain limit results in unstable solutions for any value of $Σ$ . We report that the inclusion of temperature in our analysis expands the parameter space by including more values of $κ$ . However, temperature has negligible effect on the maximum mass of the stellar profiles in all the three theories. We find that the maximum masses and radii of the stars within RR theory can have good agreement with the observational data on pulsars for all the EoSs considered and in particular, the Colpi-Wasserman-Shapiro EoS, which was ruled out in General Relativity (GR). We also find that, in contrast to the results of GR, BEC stars consistent with observations can be realised in the RR theory with smaller bosonic self-interaction strength.
↳ astro-ph.HEgr-qchep-phnucl-thGen.Rel.Grav.(2024)·8 citations
14
Color Confinement and Random Matrices -- A random walk down group manifold toward Casimir scaling --
Georg Bergner🇩🇪 · Vaibhav Gautam🇬🇧 · Masanori Hanada🇬🇧
We explain the microscopic origin of linear confinement potential with the Casimir scaling in generic confining gauge theories. In the low-temperature regime of confining gauge theories such as QCD, Polyakov lines are slowly varying Haar random modulo exponentially small corrections with respect to the inverse temperature, as shown by one of the authors (M.~H.) and Watanabe. With exact Haar randomness, computation of the two-point correlator of Polyakov loops reduces to the problem of random walk on group manifold. Linear confinement potential with approximate Casimir scaling except at short distances follows naturally from slowly varying Haar randomness. With exponentially small corrections to Haar randomness, string breaking and loss of Casimir scaling at long distance follow. Hence we obtain the Casimir scaling which is only approximate and holds only at intermediate distance, which is precisely needed to explain the results of lattice simulations. For $(1 + 1)$ -dimensional theories, there is a simplification that admits the Casimir scaling at short distances as well.
↳ hep-thhep-lathep-phnucl-thJHEP(2024)·5 citations
15
Enhanced Dilepton production near the color superconducting phase and the QCD critical point
Toru Nishimura🇯🇵 · Yasushi Nara🇯🇵 · Jan Steinheimer🇩🇪
The dilepton production yields in relativistic heavy ion collisions are investigated along isentropic trajectories in the quark (Wigner) phase within the two-flavor Nambu-Jona-Lasinio model. An enhancement of the ultra-low energy dilepton yield in the vicinity of the color superconducting (CSC) phase and the QCD critical point (QCD-CP) is found, compared to the free quark gas. Furthermore, we have found a nontrivial structure in the beam energy dependence of the ultra-low energy dilepton yield. A local maximum and minimum of the dilepton yield as a function of entropy per baryon emerge when the trajectories are close to both locations of the CSC phase transition line and the QCD-CP. Only the maximum appears in the scenario without the CSC phase but with the QCD-CP. On the other hand, when only the CSC phase is considered, the dilepton yield monotonically increases as the beam energy decreases. These distinctive patterns could potentially serve as signals of the CSC phase and QCD-CP. In addition, it is found that the dilepton production yield and the location of the minimum strongly depend on the value of diquark coupling, suggesting the possibility that the value of the diquark coupling may be extracted from experimental data.
↳ hep-phnucl-exnucl-thEPJA(2024)·10 citations
16
Quark-photon vertex in confining models
C. Mena🇧🇷 · L. F. Palhares (Rio de Janeiro State University)🇧🇷
We compute the one-loop quark-photon vertex and the quark magnetic moment in three different models with an infrared-modified gluon propagator, namely: the massive (Curci-Ferrari-like) model, the Gribov-Zwanziger model, and the Refined Gribov-Zwanziger model. We show results for the $F_{2}$ form factor and analyze the role played by the mass parameters associated with the confined gluon in these models. Using the framework of the Constituent Quark Model, we further construct the observable proton magnetic moment including the effects of QCD interactions generated by the different confining models. Our results show that there is no qualitative observable difference stemming from the presence of complex-conjugated poles. On the other hand, quantitative differences between the various confining models can be sizable, so that observable constraints would in principle be possible, provided one has sufficient information about the constituent quark mass and the QCD running coupling.
↳ hep-phhep-thnucl-th4 citations
17
Roberge-Weiss periodicity and singularity in hadron resonance gas model with excluded volume effects
Riki Oshima🇯🇵 · Hiroaki Kouno🇯🇵 · Kouji Kashiwa🇯🇵
Quantum chromodynamics (QCD) with pure imaginary baryon number chemical potential mu =i theta T, where T is temperature and theta is a real number, has the Roberge-Weiss periodicity. We study the theta-dependence of the baryon number density and the pressure in the hadron resonance gas model with excluded volume effects of baryons. It is shown that the baryon number density and the pressure are smooth periodic functions of theta at low or high temperature. However, they have singular behavior at theta =(2k+1)pi where k is an integer, when T sim 211MeV. This temperature is consistent with the Roberge-Weiss transition temperature TRW obtained by lattice QCD simulations. This singularity can be explained by the dual excluded volume effects in which the roles of point-like and non point-like particles are exchanged each other in the ordinary excluded volume effects. It is also indicated that the excluded volume effect is visible just below TRW and is directly detectable by the lattice QCD simulation at finite theta. We compare the results with the one obtained by the Polyakov-loop extended Nambu-Jona-Lasinio model.
↳ hep-phhep-latnucl-thPRD(2025)·4 citations
18
Contrasting observables related to the $N^{*} (1535)$ from the molecular or a genuine structure
Hai-Peng Li🇨🇳 · Jing Song🇨🇳 · Wei-Hong Liang🇨🇳 · R. Molina🇨🇳 · E. Oset🇨🇳
In this work we compare the predictions for the scattering length and effective range of the channels $K^{0} Σ^{+}, K^{+} Σ^{0}, K^{+} Λ$ and $η p$ , assuming the $N^{*} (1535)$ state as a molecular state of these channels, or an original genuine state, made for instance from three quarks. Looking at very different scenarios, what we conclude is that the predictions of these two pictures are drastically different, to the point that we advise the measurement of these magnitudes, accessible for instance by measuring correlation functions, in order to gain much valuable information concerning the nature of this state.
↳ hep-phnucl-thEPJC(2024)·17 citations
19
An NJL model analysis of a magnetised nonextensive QCD medium
Chowdhury Aminul Islam🇩🇪
We investigate the effect of a background magnetic field when applied to a nonextensive QCD medium in a $2 + 1$ flavour Nambu\textemdash Jona-Lasinio model. The effect of a constant as well as an $e B$ -dependent coupling is considered. For the constant coupling, the well-known magnetic catalysis effect is observed with reduced strength in both the condensates and the transition temperatures compared to the standard extensive medium. In the case of a field-dependent coupling, we observe a competition between the nonextensive parameter, $q$ and $e B$ . With sufficiently high $q$ -values, the phenomenon of inverse magnetic catalysis \textemdash\, a well-known trait in effective models featuring $e B$ -dependent coupling, appears to be eliminated within the range of magnetic fields examined in our present study.
↳ hep-phnucl-thEPJA(2024)·6 citations
20
Systematics of the low-energy electric dipole strength in the Sn isotopic chain
M. Markova (1)🇳🇴 · P. von Neumann-Cosel (2)🇩🇪 · E. Litvinova (3,4,5) ((1) Department of Physics, University of Oslo, Oslo, Norway, (2) Institut fuer Kernphysik, Technische Universitaet Darmstadt, Darmstadt, Germany, (3) Department of Physics, Western Michigan University, Kalamazoo, Michigan, USA, (4) National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan, USA, (5) GANIL, CEA/DRF-CNRS/IN2P3, Caen, France)🇺🇸
We present a systematic study of the mass dependence of the low-energy electric dipole strength (LEDS) in Sn isotopes in the range $A = 111 - 124$ based on data obtained with the Oslo method and with relativistic Coulomb excitation in forward-angle ( $p, p^{'}$ ) scattering. The combined data cover an energy range of $2 - 20$ MeV which permits, with minimal assumptions, a decomposition of the total strength into the contribution from the low-energy tail of the isovector giant dipole resonance (IVGDR) and possible resonance-like structures on top of it. In all cases, a resonance peaked at about 8.3 MeV is observed, exhausting an approximately constant fraction of the Thomas-Reiche-Kuhn (TRK) sum rule with a local maximum at $^{120}$ Sn which might be related to shell structure effects. For heavier isotopes ( $A \geq 118$ ) a consistent description of the data requires the inclusion of a second resonance centered at 6.5 MeV, representing the isovector response of the pygmy dipole resonance (PDR). Its strength corresponds to a small fraction of the total LEDS only and shows an approximately linear dependence on mass number. The experimental results are also compared to ab initio-based microscopic calculations to investigate the importance of an inclusion of quasiparticle vibration coupling (qPVC) for a realistic description of the LEDS. A possible interpretation of the experimentally observed two-bump structure is given.
↳ nucl-exnucl-thPLB(2025)·15 citations
21
Magnetic field at nucleus for ionized atoms
Andrzej Tucholski · Zygmunt Patyk
The study of the magnetic properties of atoms and nuclei was performed. A linear dependence between the strength of the magnetic field at the nucleus and the effective charge divided by the major quantum number were analyzed and explained. The calculations of the magnetic field at the nucleus were done for a wide set of electron configurations within the framework of relativistic Dirac-Hartree-Fock method. Results are compared to experimental results of $g$ -factor measurements.
↳ physics.atom-phnucl-th0 citations

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