New articles on nucl-th

[1] 2009.08741

$J/ψ$ near $T_c$

We calculate the mass shift and thermal decay width of the $J/\psi$ near the QCD transition temperature $T_c$ by imposing two independent constraints on these variables that can be obtained first by solving the Schr\"odinger equation and second from the QCD sum rule approach. While the real part of the potential is determined by comparing the QCD sum rule result for charmonium and the D meson to that from the potential model result, the imaginary potential is taken to be proportional to the perturbative form multiplied by a constant factor, which in turn can be determined by applying the two independent constraints. The result shows that the binding energy and the thermal width becomes similar in magnitude at around $T=1.09T_c$, above which the sum rule analysis also becomes unstable, strongly suggesting that the $J/\psi$ will melt slightly above $T_c$.

[2] 2009.08858

Benchmark of medium-induced radiative energy loss model for heavy-ion collisions

We report on a benchmark calculation of the in-medium radiative energy loss of low-virtuality jet partons within the EPOS3-Jet framework. The radiative energy loss is based on an extension of the Gunion-Bertsch matrix element for a massive projectile and a massive radiated gluon. On top of that, the coherence (LPM effect) is implemented by assigning a formation phase to the trial radiated gluons in a fashion similar to the approach in JHEP 07 (2011), 118, by Zapp, Stachel and Wiedemann. In a calculation with a simplified radiation kernel, we reproduce the radiation spectrum reported in the approach above. The radiation spectrum produces the LPM behaviour $dI/d\omega\propto\omega^{-1/2}$ up to an energy $\omega=\omega_c$, when the formation length of radiated gluons becomes comparable to the size of the medium. Beyond $\omega_c$, the radiation spectrum shows a characteristic suppression due to a smaller probability for a gluon to be formed in-medium. Next, we embed the radiative energy loss of low-virtuality jet partons into a more realistic "parton gun" calculation, where a stream of hard partons at high initial energy $E_\text{ini}=100$ GeV and initial virtuality $Q^2=E^2$ passes through a box of QGP medium with a constant temperature. At the end of the box evolution, the partons are hadronized using Pythia 8, and the jets are reconstructed with the FASTJET package. We find that the full jet energy loss in such scenario approaches a ballpark value reported by the ALICE collaboration. However, the calculation uses a somewhat larger value of the coupling constant $\alpha_s$ to compensate for the missing collisional energy loss of the low-virtuality jet partons.

[3] 2009.08885

New equations of state constrained by nuclear physics, observations, and high-density QCD calculations

We present new equations of state for applications in core-collapse supernova and neutron star merger simulations. We start by introducing an effective mass parametrization that is fit to recent microscopic calculations up to twice saturation density. This is important to capture the predicted thermal effects, which have been shown to determine the proto-neutron star contraction in supernova simulations. The parameter range of the energy-density functional underlying the equation of state is constrained by chiral effective field theory results at nuclear densities as well as by functional renormalization group computations at high densities based on QCD. We further implement observational constraints from measurements of heavy neutron stars, the gravitational wave signal of GW170817, and from the recent NICER results. Finally, we study the resulting allowed ranges for the equation of state and for properties of neutron stars, including the predicted ranges for the neutron star radius and maximum mass.

[4] 2009.08887

Isobaric analog state energy in deformed nuclei: a toy model

A formula to evaluate the effects of a general deformation on the Coulomb direct contribution to the energy of the Isobaric Analog State (IAS) is presented and studied via a simple yet physical model. The toy model gives a reasonable account of microscopic deformed Hartree-Fock-Bogolyubov (HFB) calculations in a test case, and provides a guidance when predicting unknown IAS energies. Thus, deformed HFB calculations, to predict the IAS energies, are performed for several neutron-deficient medium-mass and heavy nuclei which are now planned to be studied experimentally.

[5] 2009.08911

High-accuracy calculation of the deuteron charge and quadrupole form factors in chiral effective field theory

We present a comprehensive analysis of the deuteron charge and quadrupole form factors based on the latest two-nucleon potentials and charge density operators derived in chiral effective field theory. The single- and two-nucleon contributions to the charge density are expressed in terms of the proton and neutron form factors, for which the most up-to-date empirical parametrizations are employed. By adjusting the fifth-order short-range terms in the two-nucleon charge density operator to reproduce the world data on the momentum-transfer dependence of the deuteron charge and quadrupole form factors, we predict the values of the structure radius and the quadrupole moment of the deuteron: $r_{\rm str}=1.9729\substack{+0.0015\\ -0.0012}\ \text{fm},\ Q_d=0.2854\substack{+0.0038\\ -0.0017}\ \text{fm}^2. $ A comprehensive and systematic analysis of various sources of uncertainty in our predictions is performed. Following the strategy advocated in our recent publication Phys. Rev. Lett. 124, 082501 (2020), we employ the extracted structure radius together with the accurate atomic data for the deuteron-proton mean-square charge radii difference to update the determination of the neutron charge radius, for which we find: $r_n^2=-0.105\substack{+0.005\\ -0.006} \, \text{fm}^2$. Given the observed rapid convergence of the deuteron form factors in the momentum-transfer range of $Q \simeq 1-2.5$ fm$^{-1}$, we argue that this intermediate-energy domain is particularly sensitive to the details of the nucleon form factors and can be used to test different parametrizations.

[6] 2009.08913

Baryon stopping as a relativistic Markov process in phase space

We reconsider baryon stopping in relativistic heavy-ion collisions in a nonequilibrium-statistical framework. The approach combines earlier formulations based on quantum chromodynamics with a relativistic diffusion model through a suitably derived fluctuation-dissipation relation, thus allowing for a fully time-dependent theory that is consistent with QCD. We use an existing framework for relativistic stochastic processes in spacetime that are Markovian in phase space, and adapt it to derive a Fokker-Planck equation in rapidity space, which is solved numerically. The time evolution of the net-proton distribution function in rapidity space agrees with stopping data from the CERN Super Proton Synchrotron and the BNL Relativistic Heavy Ion Collider.

[7] 2009.08781

Effect of neutrino magnetic moment and charge radius on the neutrino mean free path in dense matter with medium modifications of the nucleon form factors

A study of neutrino charge radius and magnetic moment on the neutrino electroweak interaction with dense nuclear matter are performed by considering medium modifications of the weak and electromagnetic nucleon form factors of the constituents of matter. A relativistic mean field model and the quark-meson coupling model are respectively adopted for the in-medium effective nucleon mass and nucleon form factors. We find that the cross sections of neutrino scattering in cold nuclear medium increase when neutrino form factors as well as the in-medium modifications of the nucleon weak and electromagnetic form factors are simultaneously taken into account. The cross section increase results in the decrease of the neutrino mean free path, in particular at larger neutrino magnetic moment and charge radius. The largest quenching of the neutrino mean free path is estimated to be about 15--70\% for $\mu_\nu = 5 \times 10^{-10} \mu_B$ and $R_\nu = 3.5 \times 10^{-5}~\textrm{MeV}^{-1}$ compared with the values obtained without the neutrino magnetic moment and charge radius. The decrease of the neutrino mean free path is expected to decelerate the cooling of neutron stars.