A procedure is suggested for calculating electroexcitation multipoles to order 1/$M_N$${}^2$ with only the operators required in the calculations to order 1/$M_N$. It is also shown that calculations to order 1/$M_N$${}^2$ cannot account for the contributions of a fully relativistic calculation of the transverse response.

We calculate a novel “magnetic contribution” to the dilepton spectrum in heavy-ion collisions arising from interaction of relativistic quarks with intense magnetic field. Synchrotron radiation by quarks, which can be approximated by the equivalent photon flux, is followed by dilepton decay of photons in an intense magnetic field. We argue that the “magnetic contribution” dominates the dilepton spectrum at low lepton energies, whereas a conventional photon dilepton decay dominates at higher lepton energies.

Exact analytical solution for the space-time evolution of electromagnetic field in electrically conducting nuclear matter produced in heavy-ion collisions is discussed. It is argued that the parameter that controls the strength of the matter effect on the field evolution is $\sigma \gamma b$, where $\sigma$ is electrical conductivity, $\gamma$ is the Lorentz boost-factor, and $b$ is the characteristic transverse size of the matter. When this parameter is of the order 1 or larger, which is the case at the Relativistic Heavy Ion Collider and the Large Hadron Collider, the space-time dependence of the electromagnetic field completely differs from that in vacuum.

Based on a multiphase transport model, the measured jet fragmentation function ratio of $\text{Pb}+\text{Pb}$ collisions to $p+p$ collisions in CERN Large Hadron Collider experiments is decomposed into two parts, corresponding to the two contributions of jet hadronization from fragmentation and coalescence. The results suggest an existence of distinct competitions between two jet hadronization mechanisms for different $\xi =\text{ln}(1/z)$ ranges in different centrality bins. The jet fragmentation functions for different types of hadrons (mesons and baryons) are proposed as a good probe to study the competition between fragmentation and coalescence for the jet hardonization in high-energy heavy-ion collisions.

The nuclear matter symmetry energy $C_{\mathrm{sym}}\left(\rho \right)$ and its slope parameter $L$ are studied using local density approximation. With this method, the symmetry energy of nuclear matter can be deduced from matter density distributions of finite nuclei. By systematically analyzing the extracted $L$ for different isotopes, the variation trends of values of extracted $L$ along isotopic chains can be obtained. The study can explain why the neutron rich nuclei in isotopic chains such as ${}^{208}$Pb can be used to extract $L$ under local density approximation. By studying the regularity of extracted $L$ for different isotopic chains, we finally obtain the value of $L$ and its error bar: $L=66\pm 7$ MeV. Besides, the density dependence parameter $\gamma$ is constrained to be $0.69\pm 0.07$ for the ansatz of symmetry energy $C_{\mathrm{sym}}\left(\rho \right)=C_{\mathrm{sym}}\left({\rho }_0\right){\left(\frac{\rho }{{\rho }_0}\right)}^{\gamma }$.

The fusion cross sections, barrier, and spin distributions of stable and unstable nuclei are investigated through a coupled-channel approach using a density and energy-dependent effective Brueckner $G$-matrix interaction. Calculations are carried out for the fusion reactions ${}^{16,18,20,22,24}\mathrm{O}+{}^{58}$Ni and ${}^{28}\mathrm{Si}+{}^{58,62,64}$Ni. Microscopic Skyrme-Hartree-Fock proton and neutron density distributions are used in the calculations. It is found that the energy dependence of the interaction potential enhances the fusion cross section, where it increases with increasing energy due to the decrease in the interaction barrier. The density dependence of the interaction is found to be of great importance, especially for unstable nuclei, since it directly relates the fusion cross section with the nuclear structure. The effect of the neutron skin is found to largely increase the fusion cross section and spin distribution due to the increase in the overlap region. The coupling to the inelastic excited states strongly enhances the fusion cross sections. The effect of the difference between the nuclear and charge deformations is also investigated.

We study the kinetics of antibaryon production and annihilation in an expanding system, assuming that it is spatially homogeneous and chemically equilibrated at the initial stage. By solving simplified rate equations for (anti)baryon abundances we study the deviations from chemical equilibrium at late stages. The calculations are done for different expansion rates and net-baryon-to-entropy ratios, covering the conditions from the early universe to heavy-ion collisions. Our analysis includes both stable (anti)baryons and resonances. We conclude that residual antibaryon abundances are very sensitive to the time scales of expansion. Our calculations naturally explain noticeable deviations of $\overline{p}/\pi$ and $p/\pi$ ratios observed in nuclear collisions at Large Hadron Collider (LHC) energy from the thermal model predictions. We conclude that at high bombarding energies the chemical freeze-out of (anti)baryons should occur at lower temperatures as compared to mesons.

Correlators between event planes of different harmonics in relativistic heavy-ion collisions have the potential to provide crucial information on the initial state of the matter formed in these collisions. We present a new procedure for analyzing such correlators, which is less demanding in terms of detector acceptance than the one used recently by the ATLAS Collaboration to measure various two-plane and three-plane correlators in Pb-Pb collisions at the Large Hadron Collider (LHC). It can also be used unambiguously for quantitative comparison between theory and data. We use this procedure to carry out realistic simulations within a multiphase transport (AMPT) model. Our theoretical results are in excellent agreement with the ATLAS data, in contrast with previous hydrodynamic calculations which only achieved qualitative agreement. We present predictions for new correlators, in particular four-plane correlators, which can easily be analyzed with our new method.

An exactly solvable model for a description of the two-neutrino double-$\beta$ decay transition of the Fermi type is considered. By using perturbation theory an explicit dependence of the two-neutrino double-$\beta$ decay matrix element on the like-nucleon pairing, particle-particle, and particle-hole proton-neutron interactions is found by assuming a weak violation of isospin symmetry of the Hamiltonian expressed with generators of the SO(5) group. It is found that there is a dominance of double-$\beta$ decay transition through a single state of the intermediate nucleus. Then, an energy-weighted sum rule connecting $\Delta Z=2$ nuclei is presented and discussed. It is suggested that this sum rule can be exploited to study the residual interactions of the nuclear Hamiltonian.

We propose an axisymmetric angle-dependent gap (ADG) state with the broken rotational symmetry in isospin-asymmetric nuclear matter. In this state, the deformed Fermi spheres of neutrons and protons increase the pairing probabilities along the axis of symmetry breaking near the average Fermi surface. We find that the state possesses lower free energy and larger gap value than the angle-averaged gap state at large isospin asymmetries. These properties are mainly caused by the coupling of different $m_j$ components of the pairing gap. Furthermore, we find the transition from the ADG state to the normal state is of second order and the ADG state vanishes at the critical isospin asymmetry ${\alpha }_c$ where the angle-averaged gap vanishes.

Experimental data at Relativistic Heavy Ion Collider and Super Proton Synchrotron energies suggest a systematic correlation between yield ratio $\overline{p}/p$ and $K^{-}/K^{+}$, which reveal some universality of hadron production in relativistic heavy ion collisions. We propose an explanation based on the quark combination mechanism that focuses on the production asymmetry between baryons and antibaryons. We start from the basic ideas of quark combination to carry out a general analysis of the properties of the global production of baryons and mesons and obtain the yields of baryons, antibaryons, and mesons as functions of the number of constituent quarks and antiquarks just before hadronization. In particular, we study effects of quark-antiquark asymmetry on the ratio of (anti-)baryons to mesons and that of antibaryons to baryons. We use these formula to well explain the data of $\overline{p}/p$ and $K^{-}/K^{+}$ at different of collision energies and rapidities and suggest further measurements at moderate RHIC energies in the mid-forward rapidity regions to make the decisive test of this universality.

Background: The pseudospin symmetry (PSS) has been studied extensively for bound states. Recently, we justified rigorously that the PSS in single-particle resonant states is exactly conserved when the attractive scalar and repulsive vector potentials of the Dirac Hamiltonian have the same magnitude but opposite sign [Phys. Rev. Lett. 109, 072501 (2012)].

Purpose: To understand more deeply the PSS in single-particle resonant states, we focus on several issues related to the exact conservation and breaking mechanism of the PSS in single-particle resonances. In particular, we are interested in how the energy and width splittings of PS partners depend on the depth of the scalar and vector potentials.

Methods: We investigate the asymptotic behaviors of radial Dirac wave functions. Spherical square-well potentials are employed in which the PSS breaking part in the Jost function can be well isolated. By examining the zeros of Jost functions corresponding to small components of the radial Dirac wave functions, general properties of the PSS are analyzed.

Results: By examining the Jost function, the occurrence of intruder orbitals is explained and it is possible to trace continuously the PS partners from the PSS limit to the case with a finite potential depth. The dependence of the PSS in resonances as well as in bound states on the potential depth is investigated systematically. We find a threshold effect in the energy splitting and an anomaly in the width splitting of pseudospin partners when the depth of the single-particle potential varies from zero to a finite value.

Conclusions: The conservation and the breaking of the PSS in resonant states and bound states share some similar properties. The appearance of intruder states can be explained by examining the zeros of Jost functions. Origins of the threshold effect in the energy splitting and the anomaly in the width splitting of PS partners, together with many other problems, are still open and should be further investigated.

The energy- and density-dependent single-particle potential for nucleons is constructed in a medium of infinite isospin-symmetric nuclear matter starting from realistic nuclear interactions derived within the framework of chiral effective field theory. The leading-order terms from both two- and three-nucleon forces give rise to real, energy-independent contributions to the nucleon self-energy. The Hartree-Fock contribution from the two-nucleon force is attractive and strongly momentum dependent, in contrast to the contribution from the three-nucleon force which provides a nearly constant repulsive mean field that grows approximately linearly with the nuclear density. Together, the leading-order perturbative contributions yield an attractive single-particle potential that is however too weak compared to phenomenology. Second-order contributions from two- and three-body forces then provide the additional attraction required to reach the phenomenological depth. The imaginary part of the optical potential, which is positive (negative) for momenta below (above) the Fermi momentum, arises at second order and is nearly inversion-symmetric about the Fermi surface when two-nucleon interactions alone are present. The imaginary part is strongly absorptive and requires the inclusion of an effective mass correction as well as self-consistent single-particle energies to improve agreement with phenomenology.

The scintillation properties of liquid helium upon the recoil of a low-energy helium atom are discussed in the context of the possible use of this medium as a detector of dark matter. It is found that the prompt scintillation yield in the range of recoil energies from a few keV to 100 keV is somewhat higher than that obtained by a linear extrapolation from the measured yield for a 5-MeV $\alpha$ particle. A comparison is made of both the scintillation yield and the charge separation by an electric field for nuclear recoils and for electrons stopped in helium.

We perform Brueckner-Hartree-Fock calculations of hypernuclear matter employing the recent Nijmegen extended soft-core 08 hyperon-nucleon and hyperon-hyperon potentials. The results are used in a generalized Skyrme-Hartree-Fock model to calculate the properties of single- and double-$\Lambda$ hypernuclei. Based on those results, estimates of the effects of hypernuclear three-body forces and other corrections are made.

Recently, two strongly intensive quantities, $\Delta [A,B]$ and $\Sigma [A,B]$, designed for the study of event-by-event fluctuations in high-energy collisions were introduced. They are defined in terms of two extensive event observables $A$ and $B$. In this paper a special normalization of the $\Delta [A,B]$ and $\Sigma [A,B]$ fluctuation measures is proposed. It ensures that they are dimensionless and yields a common scale required for a quantitative comparison of fluctuations of different, in general dimensional, extensive quantities. Namely, the properly normalized strongly intensive measures assume the value one for fluctuations given by the independent particle model, and they are equal to zero when the $A$ and $B$ observables have constant values in all collision events.

We study the production of the stable six-quark $H$ dibaryon via the $(K^{-},K^{+})$ reaction on a ${}^{12}$C target within a covariant effective Lagrangian model. The calculations are performed within a factorization approximation, in which the full production amplitude is written as a product of the amplitudes for the $K^{-}+p\to K^{+}+{\Xi }^{-}$ and ${\Xi }^{-}+p\to H$ processes. The $K^{+}{\Xi }^{-}$ production vertex is described by excitation, propagation, and decay of $\Lambda$ and $\Sigma$ resonance states in the initial collision of a $K^{-}$ meson with a target proton in the incident channel. The parameters of the resonance vertices are taken to be the same as those determined previously by describing the available data on total and differential cross sections for the $p(K^{-},K^{+}){\Xi }^{-}$ reaction within a similar model. The ${\Xi }^{-}+p\to H$ fusion process is treated within a quark model where the $H$ dibaryon is considered as a stable particle. For the $K^{+}$ meson angle fixed at 0${}^{\circ }$, the $H$ production cross section is found to be about 2.9 $\mu b/sr$ for $H$ mass just below the $\Lambda \Lambda$ threshold at a $K^{-}$ beam momentum of 1.67 GeV/$c$. This is an order of magnitude larger than the value for this quantity reported earlier in calculations performed on a ${}^3$He target using a different model for the cascade hyperon production. We have also calculated the beam momentum dependence of the $H$ production cross section and the energy spectrum of the emitted $K^{+}$ meson.

The high-spin states of the two neutron-rich nuclei ${}^{88}$Kr${}_{52}$ and ${}^{89}$Rb${}_{52}$ have been studied from the ${}^{18}$O+${}^{208}$Pb fusion-fission reaction. Their level schemes were built from triple $\gamma$-ray coincidence data, and $\gamma -\gamma$ angular correlations were analyzed in order to assign spin and parity values to most of the observed states. The two level schemes evolve from collective structures to single-particle excitations as a function of the excitation energy. Comparison with results of shell-model calculations gives the specific proton and neutron configurations which are involved to generate the angular momentum along the yrast lines.