Nuclear Theory

We investigate the properties of baryonic matter within the framework of the in-medium modified chiral soliton model by taking into account the effects of surrounding baryonic environment on the properties of in-medium baryons. The internal parameters of the model are determined based on nuclear phenomenology at nonstrange sector and fitted by reproducing nuclear matter properties near the saturation point. We discuss the equations of state in different nuclear environments such as symmetric nuclear matter, neutron and strange matters. We show that the results for the equations of state are in good agreement with the phenomenology of nuclear matter. We also discuss how the SU(3) baryons masses undergo changes in these various types of nuclear matter.

Recent experiments [Phys. Rev. Lett. 123, 092503(2019); Phys. Rev. Lett. 118, 222501 (2017)] have made remarkable progress in measurements of the isotopic fission-fragment yields of the compound nucleus 239 U, which is of great interests for fast-neutron reactors and for benchmarks of fission models. We apply the Bayesian neural network (BNN) approach to learn existing evaluated charge yields and infer the incomplete charge yields of 239 U. We found the two-layer BNN is improved compared to the single-layer BNN for the overall performance. Our results support the normal charge yields of 239 U around Sn and Mo isotopes. The role of odd-even effects in charge yields has also been studied.

[Purpose:] We infer the posterior probability distribution functions (PDFs) and correlations of nine parameters characterizing the EOS of dense neutron-rich matter encapsulating a first-order hadron-quark phase transition from the radius data of canonical NSs reported by LIGO/VIRGO, NICER and Chandra Collaborations. We also infer the quark matter (QM) mass fraction and its radius in a 1.4 M ⊙ NS and predict their values in more massive NSs. [Method:] Meta-modelings are used to generate both hadronic and QM EOSs in the Markov-Chain Monte Carlo sampling process within the Bayesian statistical framework. An explicitly isospin-dependent parametric EOS for the npeμ matter in NSs at β equilibrium is connected through the Maxwell construction to the QM EOS described by the constant speed of sound (CSS) model of Alford, Han and Prakash. [Results:] (1) The most probable values of the hadron-quark transition density ρ t / ρ 0 and the relative energy density jump there $\De\ep/\ep_t$ are ρ t / ρ 0 = 1.6 +1.2 −0.4 and $\De\ep/\ep_t=0.4^{+0.20}_{-0.15}$ at 68\% confidence level, respectively. The corresponding probability distribution of QM fraction in a 1.4 M ⊙ NS peaks around 0.9 in a 10 km sphere. Strongly correlated to the PDFs of ρ t and $\De\ep/\ep_t$, the PDF of the QM speed of sound squared $\cQMsq/c^2$ peaks at 0.95 +0.05 −0.35 , and the total probability of being less than 1/3 is very small. (2) The correlations between PDFs of hadronic and QM EOS parameters are very weak. [Conclusions:] The available astrophysical data considered together with all known EOS constraints from theories and terrestrial nuclear experiments prefer the formation of a large volume of QM even in canonical NSs.

The neutron skin thickness Δ r np in heavy nuclei has been known as one of the most sensitive terrestrial probes of the nuclear symmetry energy around 2 3 of the saturation density ρ 0 of nuclear matter. Existing neutron skin data mostly from hadronic observables suffer from large uncertainties and their extraction from experiments are often strongly model dependent. While waiting eagerly for the promised model-independent and high-precision neutron skin data for 208 Pb and 48 Ca from the parity-violating electron scattering experiments (PREX-II and CREX at JLab as well as MREX at MESA), within the Bayesian statistical framework using the Skyrme-Hartree-Fock model we infer the posterior probability distribution functions (PDFs) of the slope parameter L of the nuclear symmetry energy at ρ 0 from imagined Δ r np ( 208 Pb )=0.15 , 0.20, and 0.30 fm as well as Δ r np ( 48 Ca )=0.12 , 0.15, and 0.25 fm, with different 1σ error bars. The results are compared with the PDFs of L inferred using the same approach from the available Δ r np data for Sn isotopes from hadronic probes. They are also compared with results from a recent Bayesian analysis of the radius and tidal deformability data of canonical neutron stars from GW170817 and NICER. The neutron skin data for Sn isotopes gives L= 45.5 +26.5 −21.6 MeV surrounding its mean value or L= 53.4 +18.6 −29.5 MeV surrounding its maximum {\it a posteriori} value, respectively, with the latter smaller than but consistent with the L= 66 +12 −20 MeV from the neutron star data within their 68\% confidence intervals. In order to provide additionally useful information on L extracted from the Δ r np of Sn isotopes, the experimental error bar of Δ r np ( 208 Pb) should be at least smaller than 0.06 fm aimed by some current experiments.

We study the collision energy dependence of (anti-)deuteron and (anti-)triton production in the most central Au+Au collisions at s NN − − − √ = 7.7, 11.5, 19.6, 27, 39, 62.4 and 200 GeV, using the nucleon coalescence model. The needed phase-space distribution of nucleons at the kinetic freeze-out is generated from a new 3D hybrid dynamical model (\texttt{iEBE-MUSIC}) by using a smooth crossover equation of state (EoS) without a QCD critical point. Our model calculations predict that the coalescence parameters of (anti-)deuteron ( B 2 (d) and B 2 ( d ¯ ) ) decrease monotonically as the collision energy increases, and the light nuclei yield ratio N t N p / N 2 d remains approximately a constant with respect to the collision energy. These calculated observables fail to reproduce the non-monotonic behavior of the corresponding data from the STAR Collaboration. Without including any effects of the critical point in our model, our results serve as the baseline predictions for the yields of light nuclei in the search for the possible QCD critical points from the experimental beam energy scan of heavy ion collisions.

We analyse various flow coefficients of anisotropic momentum distribution of final state particles in mid-central ( b = 5--9 fm ) Au + Au collisions in the beam energy range E Lab = 1A??58A GeV. Different variants of the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model, namely the pure transport (cascade) mode and the hybrid mode, are employed for this investigation. In the hybrid UrQMD model, the ideal hydrodynamical evolution is integrated with the pure transport calculation for description of the evolution of the fireball. We opt for the different available equations of state (EoS) replicating the hadronic as well as partonic degrees of freedom together with possible phase transitions, viz. hadron gas, chiral + deconfinement EoS and bag model EoS, to investigate their effect on the properties of the final state particles. We also attempt to gain insights about the dynamics of the medium by studying different features of particle production such as particle ratios and net-proton rapidity distribution. The results and conclusions drawn here would be useful to understand the response of various observables to the underlying physics of the model as well as to make comparisons with the upcoming measurements of the future experiments at Facility for Antiproton and Ion Research (FAIR) and Nuclotron-based Ion Collider fAcility (NICA).

We study the beam-normal single-spin asymmetry (BNSSA) in high-energy elastic electron scattering from several spin-0 nuclei. Existing theoretical approaches work in the plane-wave formalism and predict the BNSSA to scale as ?�A/Z with the atomic number Z and nuclear mass number A . While this prediction holds for light and intermediate nuclei, a striking disagreement in both the sign and the magnitude of BNSSA was observed by the PREX collaboration for 208 Pb, coined the "PREX puzzle". To shed light on this disagreement, we go beyond the plane-wave approach which neglects Coulomb distortions known to be significant for heavy nuclei. We explicitly investigate the dependence of BNSSA on A and Z by i) including inelastic intermediate states' contributions into the Coulomb problem in the form of an optical potential, ii) by accounting for the experimental information on the A -dependence of the Compton slope parameter, and iii) giving a thorough account of the uncertainties of the calculation. Despite of these improvements, the PREX puzzle remains unexplained. We discuss further strategies to resolve this riddle.

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/dω∝ ω −1/2 up to an energy ω= ω c , when the formation length of radiated gluons becomes comparable to the size of the medium. Beyond ω 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 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 α s to compensate for the missing collisional energy loss of the low-virtuality jet partons.

The energy spectra of light-mass kaonic nuclei were investigated using the theoretical framework of the 0s -orbital model with zero-range K ¯ N and K ¯ K ¯ interactions of effective single-channel real potentials. The energies of the K ¯ NN , K ¯ NNN , K ¯ NNNN , K ¯ K ¯ N , and K ¯ K ¯ NN systems were calculated in the cases of weak- and deep-binding of the K ¯ N interaction, which was adjusted to fit the Λ(1405) mass with the energy of the K ¯ N bound state. The results qualitatively reproduced the energy systematics of kaonic nuclei calculated via other theoretical approaches. In the energy spectra of the K ¯ NN and K ¯ K ¯ NN systems, the lowest states K ¯ NN( J π ,T= 0 − ,1/2) and K ¯ K ¯ NN( 0 + ,0) were found to have binding energies approximately twice and four times as large as that of the K ¯ N(1/ 2 − ,0) state, respectively. Higher ( J π ,T) states including K ¯ NN( 1 − ,1/2) , K ¯ K ¯ NN( 0 + ,1) , and K ¯ K ¯ NN( 1 + ,1) were predicted at energies of 9--25 MeV below the antikaon-decay threshold. The effective Λ(1405) - Λ(1405) interaction in the K ¯ K ¯ NN system was also investigated via a K ¯ N+ K ¯ N -cluster model. Strong and weak Λ(1405) - Λ(1405) attractions were obtained in the S π = 0 + and S π = 1 − channels, respectively. The Λ(1405) - Λ(1405) interaction in the $$\bar{K}\bar{K} NN$ system was compared with the effective $d$-$d$ interaction in the $NNNN$ system, and the properties of dimer-dimer interactions in hadron and nuclear systems were discussed.

In this work, we present a new version of the Bohr collective Hamiltonian for triaxial nuclei within Deformation-Dependent Mass formalism (DDM) using the Hulthén potential. We shall call the developed model Z(5)-HD. Analytical expressions for energy spectra are derived by means of the recent version of the Asymptotic Iteration Method. The calculated numerical results of energies and B(E2) transition rates are compared with the experimental data, and several theoretical results from Z(5) model, the model Z(5)-H using the Hulthén potential without DDM formalism as well as theoretical predictions of Z(5)-DD model with Davidson potential using DDM formalism. The obtained results show an overall agreement with experimental data and an important improvement in respect to the other models.