The photon from neutron-proton bremsstrahlung in $p+\mathrm{Pb}$ reactions is examined as a potential probe of the neutron-skin thickness in different centralities and at different proton incident energies. It is shown that the best choice of reaction environment is about 140 MeV for the incident proton and the 95%–100% centrality for the reaction system since the incident proton mainly interacts with neutrons inside the skin of the target and thus leads to different photon production to a maximal extent. Moreover, considering two main uncertainties from both photon production probability and nucleon-nucleon cross section in the reaction, I propose to use the ratio of photon production from two reactions to measure the neutron-skin thickness because of its cancellation effects on these uncertainties simultaneously, but preserved about 13%–15% sensitivities on the varied neutron-skin thickness from 0.1 to 0.3 fm within the current experimental uncertainty range of the neutron-skin size in ${}^{208}\mathrm{Pb}$.

Measurements of complete and incomplete fusion cross sections for ${}^6\mathrm{Li}+{}^{154}\mathrm{Sm}$ have been performed at energies above the Coulomb barrier by the online $\gamma$-ray method, to investigate the effect of breakup and inelastic couplings on the complete fusion (CF) of this weakly bound system. We show that inelastic excitation couplings have non-negligible effects, when compared with the breakup effect, for deformed nuclei at energies very close to the Coulomb barrier. The average CF suppression corresponding to dynamic breakup effects was found to be around 35%. The total fusion cross section is not affected by the breakup coupling. A comparison between the ${}^6\mathrm{Li}$-induced CF suppression for three different samarium isotopes shows that the breakup effect is larger for the more spherical isotope.

Microscopic deuteron-nucleus optical potential was constructed on the basis of the nucleon-nucleus optical potentials recently obtained by the authors from approximate calculations of the mass operator of the single-particle Green function using the Skyrme forces, which in general involve additional density- and momentum-dependent terms. Both the nucleon- and deuteron-nucleus elastic scattering processes are described in a self-consistent approach using the effective nucleon-nucleon forces, which simultaneously provide a satisfactory description of nuclear structure. The calculations performed using the Watanabe-type approximation have made it possible to obtain reasonable results for describing differential cross sections and polarization observables for the elastic deuteron scattering in a wide range of target-nucleus mass numbers at different incident deuteron energies, when using several Skyrme-force variants both from literature and proposed by the authors. Contributions to elastic deuteron-nucleus scattering cross sections coming from the effects of deuteron virtual breakup have been estimated in the continuum-discretized coupled channels approach.

We report the measurement of beam-target double spin asymmetries $\left(A_{\text{LT}}\right)$ in the inclusive production of identified hadrons, $\vec{e}$ + ${}^3{\text{He}}^{\uparrow }\to h+X$, using a longitudinally polarized 5.9-GeV electron beam and a transversely polarized ${}^3\mathrm{He}$ target. Hadrons $({\pi }^{\pm },K^{\pm }$, and proton) were detected at ${16}^{\circ }$ with an average momentum $\langle P_h\rangle =2.35$ GeV/c and a transverse momentum $\left(p_T\right)$ coverage from 0.60 to 0.68 GeV/c. Asymmetries from the ${}^3\mathrm{He}$ target were observed to be nonzero for ${\pi }^{\pm }$ production when the target was polarized transversely in the horizontal plane. The ${\pi }^{+}$ and ${\pi }^{-}$ asymmetries have opposite signs, analogous to the behavior of $A_{\text{LT}}$ in semi-inclusive deep-inelastic scattering.

The integrated proton-deuteron cross section $\tilde{\sigma }$ for the case of the incident proton vector polarization $p_y^p$ and tensor polarization $P_{xz}$ of the deuteron target provides a null-test signal for time-reversal invariance violating but $P$-parity conserving (TVPC) effects. We study the null-test observable $\tilde{\sigma }$ within the Glauber theory of the double-polarized $pd$ scattering. Full spin dependence of the ordinary strong $pN$ scattering amplitudes and different types of the hypothetical TVPC $pN$ amplitudes are taken into account. We show that the contribution from the exchange of the lowest-mass meson allowed in the TVPC interaction, i.e., the $\rho$ meson, to the null-test observable $\tilde{\sigma }$ is zero. The axial $h_1$ meson exchange makes a nonzero contribution. We find that inclusion of the Coulomb interaction does not lead to divergence of the cross section $\tilde{\sigma }$ and we calculate its energy dependence at the proton beam energy 100–1000 MeV.

It has been found in recent heavy-ion experiments that the second and the third flow harmonics of direct photons are larger than most theoretical predictions. In this study, I construct effective parton phase-space distributions with in-medium interaction using quasiparticle models so that they are consistent with a lattice QCD equation of state. Then I investigate their effects on thermal photons using a hydrodynamic model. Numerical results indicate that elliptic flow and transverse momentum spectra are modified by the corrections to Fermi-Dirac and Bose-Einstein distributions.

The hydrodynamic helicity separation effect in noncentral heavy-ion collisions is investigated using the hadron-string dynamics (HSD) model. Computer simulations are done to calculate velocity and hydrodynamic helicity on a mesh in a small volume around the center of the reaction. The time dependence of hydrodynamic helicity is observed for various impact parameters and different calculation methods. Comparison with a similar earlier work is carried out. A new quantity related to jet handedness is used to probe for $p$-odd effects in the final state.

Nucleon-antinucleon annihilation in the large-$N_c$ limit of QCD in the Witten regime of fixed velocity is considered with a focus on the spin and isospin dependence of the annihilation cross section. In general, time reversal and isospin invariance restrict the annihilation cross section so that it depends on six independent energy-dependent terms. At large $N_c$, a spin-flavor symmetry emerges that acts to further restrict the dependence of the annihilation cross section to three of these terms; the other terms amount to $1/N_c$ corrections. Assuming dominance of the leading order terms, several identities are derived that relate annihilation in different spin-isospin channels. A key prediction is that for unpolarized nucleons in Witten kinematics, the proton-antiproton annihilation cross section should be equal to the proton-antineutron annihilation cross section up to corrections of relative order $1/N_c$. Unpolarized nucleon-antinucleon annihilation data appear to be consistent with this expectation.

Radiative capture rates of thermal $\mathrm{\Lambda }\mathrm{\Lambda }+\mathrm{\Xi }N$ states into a H dibaryon are calculated in the novel imaginary time method. The H dibaryon is assumed to be a bound state of $\mathrm{\Xi }N$ with spin $J^{\pi }=0^{+}$, isospin $I=0$ and strangeness $-2$. We consider the $E1$ transition to H from $\mathrm{\Xi }N (L=1)$ scattering states which mix with $\mathrm{\Lambda }\mathrm{\Lambda }(L=1)$. In order to calculate the transition rates, we formulate a coupled-channel imaginary time method by extending the one-channel formula originally proposed by Yabana and Funaki. The imaginary time method allows us to avoid the sum over all the excited thermal initial states, and thus to save computational time significantly. The transition rates are given as a function of temperature and the unknown binding energy of the H dibaryon, which we take as a parameter. It is found that the transition rate is not sensitive to the choices of the H binding energy or the strengths of the channel coupling for temperatures 3 MeV or higher.

The meson-baryon interaction in $s$ wave in the strangeness $S=-1$ sector has been studied, employing a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The parameters of the Lagrangian have been fitted to a large set of experimental data in different two-body channels, paying special attention to the $\overline{K}N\to K\mathrm{\Xi }$ reaction, which is particularly sensitive to the NLO terms. With the aim of improving the model in the $K\mathrm{\Xi }$ production channels, effects of the high spin hyperon resonances $\mathrm{\Sigma }\left(2030\right)$ and $\mathrm{\Sigma }\left(2250\right)$ have been taken into account phenomenologically.

We present the full description of a measurement of the branching ratios for the $\beta$ decay of ${}^{38}\mathrm{Ca}$. This decay includes five allowed $0^{+}\to 1^{+}$ branches and a superallowed $0^{+}\to 0^{+}$ one. With our new result for the latter, we determine its $ft$ value to be $3062.3\pm 6.8$ s, a result whose precision (0.2%) is comparable to the precision of the 13 well-known $0^{+}\to 0^{+}$ transitions used up until now for the determination of $V_{\text{ud}}$, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa matrix. The ${}^{38}\mathrm{Ca}$ superallowed transition thus becomes the first addition to this set of transitions in nearly a decade and the first for which a precise mirror comparison is possible, thus enabling an improved test of the isospin-symmetry-breaking corrections required for the extraction of $V_{\text{ud}}$.

Background: Three-nucleon forces (3NFs) have nontrivial implications on the evolution of correlations at extreme proton-neutron asymmetries. Recent ab initio calculations show that leading-order chiral interactions are crucial to obtain the correct binding energies and neutron driplines along the O, N, and F chains [A. Cipollone, C. Barbieri, and P. Navrátil, Phys. Rev. Lett. 111, 062501 (2013)].

Purpose: Here we discuss the impact of 3NFs along the oxygen chain for other quantities of interest, such has the spectral distribution for attachment and removal of a nucleon, spectroscopic factors, and radii. The objective is to better delineate the general effects of 3NFs on nuclear correlations.

Methods: We employ self-consistent Green's function (SCGF) theory which allows a comprehensive calculation of the single-particle spectral function. For the closed subshell isotopes, ${}^{14}\mathrm{O}$, ${}^{16}\mathrm{O}$, ${}^{22}\mathrm{O}$, ${}^{24}\mathrm{O}$, and ${}^{28}\mathrm{O}$, we perform calculations with the Dyson-ADC(3) method, which is fully nonperturbative and is the state of the art for both nuclear physics and quantum chemistry applications. The remaining open-shell isotopes are studied using the newly developed Gorkov-SCGF formalism up to second order.

Results: We produce complete plots for the spectral distributions. The spectroscopic factors for the dominant quasiparticle peaks are found to depend very little on the leading-order (NNLO) chiral 3NFs. The latter have small impact on the calculated matter radii, which, however, are consistently obtained smaller than experiment. Similarly, single-particle spectra tend to be too spread with respect to the experiment. This effect might hinder, to some extent, the onset of correlations and screen the quenching of calculated spectroscopic factors. The most important effect of 3NFs is thus the fine tuning of the energies for the dominant quasiparticle states, which governs the shell evolution and the position of driplines.

Conclusions: Although present chiral NNLO 3NFs interactions do reproduce the binding energies correctly in this mass region, the details of the nuclear spectral function remain at odds with the experiment showing too-small radii and a too-spread single-particle spectrum, similar to what has already been pointed out for larger masses. This suggests a lack of repulsion in the present model of $NN+3N$ interactions, which is mildly apparent already for masses in the $A=14–28$ mass range.

Complete evolution of the strongly interacting matter formed in ultrarelativistic heavy-ion collisions is studied within a coupled Boltzmann and relativistic viscous hydrodynamics approach. For the initial nonequilibrium evolution phase, we employ a multiphase transport (AMPT) model that explicitly includes event-by-event fluctuations in the number and positions of the participating nucleons as well as of the produced partons with subsequent parton transport. The ensuing near-equilibrium evolution of quark-gluon and hadronic matter is modeled within the $(2+1)$-dimensional relativistic viscous hydrodynamics. We probe the role of parton dynamics in generating and maintaining the spatial anisotropy in the preequilibrium phase. Substantial spatial eccentricities ${\varepsilon }_n$ are found to be generated in the event-by-event fluctuations in parton production from initial nucleon-nucleon collisions. For ultracentral heavy-ion collisions, the model is able to explain qualitatively the unexpected hierarchy of the harmonic flow coefficients $v_n\left(p_T\right)(n=2–6)$ observed at energies currently available at the CERN Large Hadron Collider (LHC). We find that the results for $v_n\left(p_T\right)$ are rather insensitive to the variation (within a range) of the time of switchover from AMPT parton transport to hydrodynamic evolution. The usual Grad and the recently proposed Chapman-Enskog-like (nonequilibrium) single-particle distribution functions are found to give very similar results for $v_n(n=2–4)$. The model describes well both the BNL Relativistic Heavy Ion Collider and LHC data for $v_n\left(p_T\right)$ at various centralities, with a constant shear viscosity to entropy density ratio of 0.08 and 0.12, respectively. The event-by-event distributions of $v_{2,3}$ are in good agreement with the LHC data for midcentral collisions. The linear response relation $v_n=k_n{\varepsilon }_n$ is found to be true for $n=2,3$, except at large values of ${\varepsilon }_n$, where a larger value of $k_n$ is required, suggesting a small admixture of positive nonlinear response even for $n=2,3$.

We present results of analyses of two-pion interferometry in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=7.7$, 11.5, 19.6, 27, 39, 62.4, and 200 GeV measured in the STAR detector as part of the BNL Relativistic Heavy Ion Collider Beam Energy Scan program. The extracted correlation lengths (Hanbury-Brown–Twiss radii) are studied as a function of beam energy, azimuthal angle relative to the reaction plane, centrality, and transverse mass ($m_T$) of the particles. The azimuthal analysis allows extraction of the eccentricity of the entire fireball at kinetic freeze-out. The energy dependence of this observable is expected to be sensitive to changes in the equation of state. A new global fit method is studied as an alternate method to directly measure the parameters in the azimuthal analysis. The eccentricity shows a monotonic decrease with beam energy that is qualitatively consistent with the trend from all model predictions and quantitatively consistent with a hadronic transport model.

Theoretical calculations are performed to investigate the angular momentum and Coulomb effects on fragmentation and multifragmentation in peripheral heavy-ion collisions at Fermi energies. Inhomogeneous distributions of hot fragments in the freeze-out volume are taken into account by microcanonical Markov chain calculations within the statistical multifragmentation model. Including an angular momentum and a long-range Coulomb interaction between projectile and target residues leads to new features in the statistical fragmentation picture. In this case, one can obtain specific correlations of the sizes of emitted fragments with their velocities and an emission in the reaction plane. In addition, one may see a significant influence of these effects on isotope production both in the midrapidity and in the kinematic regions of the projectile/target. The relation of this approach to the simulations of such collisions with dynamical models is also discussed.

The presence of various fissionlike reactions in heavy-ion induced reactions is a major hurdle in the path to laboratory synthesis of heavy and super-heavy nuclei. It is known that the cross section of forming a heavy evaporation residue in fusion reactions depends on the three factors—the capture cross section, probability of compound nucleus formation $P_{\mathrm{CN}}$, and the survival probability of the compound nucleus against fission. As the probability of compound nucleus formation, $P_{\mathrm{CN}}$ is difficult to theoretically estimate because of its complex dependence on several parameters; attempts have been made in the past to deduce it from the fission fragment anisotropy data. In the present work, the fragment anisotropy data for a number of heavy-ion reactions are analyzed and it is found that deduction of $P_{\mathrm{CN}}$ from the anisotropy data also requires the knowledge of the ratio of relaxation time of the $K$ degree of freedom to pre-equilibrium fission time.

Background: The isobaric yield ratio difference (IBD) method is found to be sensitive to the density difference of neutron-rich nucleus induced reaction around the Fermi energy.

Purpose: An investigation is performed to study the IBD results in the transport model.

Methods: The antisymmetric molecular dynamics (AMD) model plus the sequential decay model gemini are adopted to simulate the $140A$ MeV ${}^{58,64}\mathrm{Ni}+{}^9\mathrm{Be}$ reactions. A relative small coalescence radius $R_c=$ 2.5 fm is used for the phase space at $t=$ 500 fm/c to form the hot fragment. Two limitations on the impact parameter ($b1=0–2$ fm and $b2=0–9$ fm) are used to study the effect of central collisions in IBD.

Results: The isobaric yield ratios (IYRs) for the large-$A$ fragments are found to be suppressed in the symmetric reaction. The IBD results for fragments with neutron excess $I=$ 0 and 1 are obtained. A small difference is found in the IBDs with the $b1$ and $b2$ limitations in the AMD simulated reactions. The IBD with $b1$ and $b2$ are quite similar in the AMD + GEMINI simulated reactions.

Conclusions: The IBDs for the $I=0$ and 1 chains are mainly determined by the central collisions, which reflects the nuclear density in the core region of the reaction system. The increasing part of the IBD distribution is found due to the difference between the densities in the peripheral collisions of the reactions. The sequential decay process influences the IBD results. The AMD + GEMINI simulation can better reproduce the experimental IBDs than the AMD simulation.

We report on the determination of the electrocouplings for the transition from the proton to the $N\left(1675\right){\frac{5}{2}}^{-}$ resonance state using recent differential cross section data on $ep\to e{\pi }^{+}n$ by the CLAS collaboration at $1.8\le Q^2<4.5$ ${\mathrm{GeV}}^2$. The data have been analyzed using two different approaches, the unitary isobar model and fixed-$t$ dispersion relations. The extracted ${\gamma }^{*}p\to N\left(1675\right){\frac{5}{2}}^{-}$ helicity amplitudes show considerable coupling through the $A_{1/2}^p$ amplitude, that is significantly larger than the predicted three-quark contribution to this amplitude. The amplitude $A_{3/2}^p$ is much smaller. Both results are consistent with the predicted sizes of the meson-baryon contributions at $Q^2\ge 1.8$ ${\mathrm{GeV}}^2$ from the dynamical coupled-channel model.

We compare two approaches to describe the inner crust of neutron stars: On the one hand, the simple coexistence of a liquid (clusters) and a gas phase, and on the other hand, the energy minimization with respect to the density profile, including Coulomb and surface effects. We find that the phase-coexistence model gives a reasonable description of the densities in the clusters and in the gas, but the precision is not high enough to obtain the correct proton fraction at low baryon densities. We also discuss the surface tension and neutron skin obtained within the energy minimization.