We use the world data on the pion form factor for space-like kinematics and a technique previously used to extract the proton transverse densities to extract the transverse pion charge density and its uncertainty due the incomplete knowledge of the pion form factor at large values of $Q^2$ and the experimental uncertainties. The pion charge density at small values of impact parameter $b<$ 0.1 fm is dominated by this incompleteness error while the range between 0.1–0.3 fm is relatively well constrained. A comparison of pion and proton transverse charge densities shows that the pion is denser than the proton for values of $b<0.2\mathrm{fm}$. The pion and proton transverse charge densities seem to be the same for values of $b=0.3–0.6$ fm. Future data from Thomas Jefferson National Accelerator Facility (JLab) 12 GeV and the Electron-Ion Collider (EIC) will increase the dynamic extent of the form factor data to higher values of $Q^2$ and thus reduce the uncertainties in the extracted pion transverse charge density.

The inclusive polarized structure functions of the proton and deuteron, $g_1^p$ and $g_1^d$, were measured with high statistical precision using polarized 6 GeV electrons incident on a polarized ammonia target in Hall B at Jefferson Laboratory. Electrons scattered at laboratory angles between 18 and 45 degrees were detected using the CEBAF Large Acceptance Spectrometer (CLAS). For the usual deep inelastic region kinematics, $Q^2>1$ ${\mathrm{GeV}}^2$ and the final-state invariant mass $W>2$ GeV, the ratio of polarized to unpolarized structure functions $g_1/F_1$ is found to be nearly independent of $Q^2$ at fixed $x$. Significant resonant structure is apparent at values of $W$ up to 2.3 GeV. In the framework of perturbative quantum chromodynamics, the high-$W$ results can be used to better constrain the polarization of quarks and gluons in the nucleon, as well as high-twist contributions.

Elastic angular distributions of the ${}^6\mathrm{He}$ + ${}^9\mathrm{Be}$ scattering at $E_{\mathrm{lab}}=16.2$ and 21.3 MeV have been analyzed in the context of the optical model. The projectile-target optical potential was calculated in a cluster model where the contributions from the fragment target $\left(\alpha {-}^9\mathrm{Be}\right)$ and the dineutron target $\left(2n{-}^9\mathrm{Be}\right)$ are separated and the latter was searched to reproduce the experimental data. The total reaction cross sections for the ${}^6\mathrm{He}$$+{}^9\mathrm{Be}$ system have been obtained, and the error bars have been estimated considering the spread between the present optical model and previous coupled channels and continuum discretized coupled-channels calculations. The cross sections have been reduced and compared in a systematics involving tightly bound, weakly bound, and the exotic ${}^6\mathrm{He}$ projectiles, all on ${}^9\mathrm{Be}$ target. An analysis of the enhancements observed in the total reaction cross section induced by ${}^6\mathrm{He}$ on light, medium mass, and heavy targets is presented.

We study charge-exchange excitations in doubly magic nuclei by using a self-consistent Hartree-Fock plus random phase approximation model. We use four Gogny-like finite-range interactions, two of them containing tensor forces. We investigate the effects of the various parts of the tensor forces in the two computational steps of our model, and we find that their presence is not negligible and improves the agreement with the experimental data.

The focus of the present article is to address the effects of the role of a neutron transfer channel in the enhancement of sub-barrier fusion excitation function data of various heavy-ion systems by using an energy-dependent Woods-Saxon potential (EDWSP) model in conjunction with the one-dimensional Wong's formula and the coupled-channel model by using the code ccfull. The effects of coupling to neutron transfer channels are found to have dominance over the coupling to low-lying surface vibrational states, such as the $2{}^{+}$ and $3{}^{-}$ vibrational states. Furthermore, the influence of inelastic surface excitations and the effects of six neutron transfer channels with positive ground state $Q$ values are mocked up by the EDWSP model.

Using an attractive surface delta interaction we obtain wave functions for two protons (or proton holes) in the $f_{5/2}$ and $p_{3/2}$ shells. We take the single-particle energies to be degenerate. We obtain the remarkable result that the $g$ factors of the lowest $2^{+}$ and the lowest $4^{+}$ states are equal to 1. We find that only the orbital part of the $g$ factors contributes—the spin part cancels out. Shell-model calculations are also performed for these same $g$ factors in a larger model space and with realistic effective interactions.

Kinetic energy spectra, angular distributions, and cross sections of projectilelike fragments (PLFs) with $Z_{\mathrm{PLF}}=3-7$ have been measured in ${}^{16}\mathrm{O}+{}^{89}\mathrm{Y}$ reaction at $E_{\mathrm{lab}}=62.2$, 73.4, 78.5, and 83.5 MeV respectively. Comparison of angular distributions of PLFs, particularly of nitrogen (N), at different beam energies showed increasing contribution from overlapping collision trajectories at higher beam energies. Angular distributions of PLFs became more forward peaked with the amount of mass transfer indicating an increasing overlap of the projectile and the target nuclei with increasing mass transfer. PLF cross sections could be reasonably explained by the modified sum-rule model except for carbon (C) indicating the role of alpha cluster structure of ${}^{16}\mathrm{O}$ nucleus in the transfer process. Large cross section for PLF emitted in the α transfer channel in ${}^{16}\mathrm{O}+{}^{89}\mathrm{Y}$ reaction compared to that in ${}^{19}\mathrm{F}+{}^{89}\mathrm{Y}$ reaction further supported this observation.

Saturation properties of the JISP16 $NN$ interaction are studied in symmetric nuclear matter calculations, with special attention paid to the convergence properties with respect to the number of partial waves. We also present results of pure neutron matter calculations with the JISP16 interaction.

We discuss the building blocks for a consistent inclusion of chiral three-nucleon ($3N$) interactions into ab initio nuclear structure calculations beyond the lower $p$ shell. We highlight important technical developments, such as the similarity renormalization group (SRG) evolution in the $3N$ sector, a $JT$-coupled storage scheme for $3N$ matrix elements with efficient on-the-fly decoupling, and the importance-truncated no-core shell model with $3N$ interactions. Together, these developments make converged ab initio calculations with explicit $3N$ interactions possible also beyond the lower $p$ shell. We analyze in detail the impact of various truncations of the SRG-evolved Hamiltonian, in particular the truncation of the harmonic-oscillator model space used for solving the SRG flow equations and the omission of the induced beyond-$3N$ contributions of the evolved Hamiltonian. Both truncations lead to sizable effects in the upper $p$ shell and beyond and we present options to remedy these truncation effects. The analysis of the different truncations is a first step towards a systematic uncertainty quantification of all stages of the calculation.

We match three hadronic equations of state at low energy densities to a perturbatively computed equation of state of quarks and gluons at high energy densities. One of them includes all known hadrons treated as point particles, which approximates attractive interactions among hadrons. The other two include, in addition, repulsive interactions in the form of excluded volumes occupied by the hadrons. A switching function is employed to make the crossover transition from one phase to another without introducing a thermodynamic phase transition. A ${\chi }^2$ fit to accurate lattice calculations with temperature $100<T<1000$ MeV determines the parameters. These parameters quantify the behavior of the QCD running gauge coupling and the hard core radius of protons and neutrons, which turns out to be $0.62\pm 0.04$ fm. The most physically reasonable models include the excluded-volume effect. Not only do they include the effects of attractive and repulsive interactions among hadrons, but they also achieve better agreement with lattice QCD calculations of the equation of state. The equations of state constructed in this paper do not result in a phase transition, at least not for the temperatures and baryon chemical potentials investigated. It remains to be seen how well these equations of state will represent experimental data on high-energy heavy-ion collisions when implemented in hydrodynamic simulations.

I have computed widths for $2p$ decay of ${}^{16}\mathrm{Ne}$ to ${}^{14}\mathrm{O}+2p$. For both simultaneous and sequential decay, my calculated widths are considerably smaller than other theoretical values—all of which are considerably smaller than the most recent experimental value and a recent upper limit.

In a Monte Carlo Hauser-Feshbach statistical framework, we describe spectra, average multiplicities, average energy, and multiplicity distributions of the prompt $\gamma$ rays produced in the thermal neutron-induced fission of ${}^{235}\mathrm{U}$ and ${}^{239}\mathrm{Pu}$, and the spontaneous fission of ${}^{252}\mathrm{Cf}$. Comparisons against recent experimental data show reasonable agreement in all cases investigated, after adjustment of the initial spin distribution in the fission fragments. In particular, when we include in the calculation the Doppler broadening we obtain a qualitatively good description of the measured low-energy spectra, where contributions from collective discrete transitions in specific fragments can be identified. At higher energies, both the calculated neutron and $\gamma$-ray spectra are softer than experimental data. The impact of selected model parameters on the prompt neutron and $\gamma$-ray spectra is analyzed. Finally, we present the prompt $\gamma$ spectrum and multiplicity distribution for the neutron-induced fission of ${}^{235}\mathrm{U}$ for 5.5 MeV neutron incident energy, just below the threshold for second-chance fission.

In this paper we present results from the first high-precision prompt-$\gamma$-ray spectral measurements from the reaction ${}^{241}\mathrm{Pu}$($n_{\mathrm{th}}$, $f$). Apart from one recent experiment, no data are reported in the literature for this fissioning system, which motivated a new dedicated experiment. We have measured prompt-fission $\gamma$ rays with three cerium-doped $\mathrm{La}{\mathrm{Br}}_3$ (two $5.08\text{cm}\times 5.08$ cm and one $7.62\text{cm}\times 7.62$ cm) and one $\mathrm{Ce}{\mathrm{Br}}_3$ ($5.08\text{cm}\times 5.08$ cm) scintillation detectors, which all exhibit excellent timing and good energy resolution. The average $\gamma$-ray multiplicity was determined to be ${\overline{\nu }}_{\gamma }=(8.21\pm 0.09)$ per fission, the average energy to be ${\epsilon }_{\gamma }=(0.78\pm 0.01)$ MeV, and the total energy to be $E_{\gamma ,\text{tot}}=(6.41\pm 0.06)$ MeV as the weighted average from all detectors. Since the results from all detectors are in excellent agreement, and the total released $\gamma$ energy is modestly higher than the one in the present evaluated nuclear data files, we suspect that the underestimation of the prompt-$\gamma$ heating in nuclear reactors is due to fast-neutron-induced fission on ${}^{238}\mathrm{U}$ or rather from fission induced by $\gamma$ rays from neutron capture in the construction material.

The compound nucleus (CN) fusion/formation probability $P_{CN}$ is defined and its detailed variations with the CN excitation energy $E^{*}$, center-of-mass energy $E_{\mathrm{c}.\mathrm{m}.}$, fissility parameter $\chi$, CN mass number $A_{CN}$, and Coulomb interaction parameter $Z_1{Z}_2$ are studied for the first time within the dynamical cluster-decay model (DCM). The model is a nonstatistical description of the decay of a CN to all possible processes. The (total) fusion cross section ${\sigma }_{\mathrm{fusion}}$ is the sum of the CN and noncompound nucleus (nCN) decay cross sections, each calculated as the dynamical fragmentation process. The CN cross section ${\sigma }_{CN}$ is constituted of evaporation residues and fusion-fission, including intermediate-mass fragments, each calculated for all contributing decay fragments ($A_1$, $A_2$) in terms of their formation and barrier penetration probabilities $P_0$ and $P$. The nCN cross section ${\sigma }_{\mathit{nCN}}$ is determined as the quasi-fission (qf) process, where $P_0=1$ and P is calculated for the entrance-channel nuclei. The DCM, with effects of deformations and orientations of nuclei included in it, is used to study the $P_{CN}$ for about a dozen “hot” fusion reactions forming a CN of mass number $A\sim 100$ to superheavy nuclei and for various different nuclear interaction potentials. Interesting results are that $P_{CN}=1$ for complete fusion, but $P_{CN}<1$ or $P_{CN}\ll 1$ due to the nCN contribution, depending strongly on different parameters of the entrance-channel reaction but found to be independent of the nuclear interaction potentials used.

The redistribution in momentum space of heavy quarks via their interactions in the quark-gluon plasma is an excellent probe of the heavy quark coupling strength to the medium. We utilize a Monte Carlo Langevin calculation for tracking heavy quark-antiquark pairs embedded in a viscous hydrodynamic space-time evolution. We find that the nuclear modification factor $\left(R_{\mathrm{AA}}\right)$ for charm quarks is relatively insensitive to the coupling to the quark-gluon plasma at early times where the highest temperatures are achieved. In contrast the azimuthal angular correlation of charm and anticharm quarks is extremely sensitive to the early time evolution. For beauty quarks the situation is reversed in terms of sensitivity. This work identifies the kinematic distributions of the heavy quarks with the greatest sensitivity, and must be followed by tests of whether they survive hadronization, in particular if recombination is dominant.

We compute the transport coefficients that appear in the fluid-dynamical equations for the bulk viscous pressure and shear-stress tensor using the 14-moment approximation in the limit of small, but finite, masses. In this limit, we are able to express all these coefficients in terms of known thermodynamic quantities, such as the thermodynamic pressure, energy density, and the velocity of sound. We explicitly demonstrate that the ratio of bulk viscosity to bulk relaxation time behaves very differently, as a function of temperature, than the ratio of shear viscosity to shear relaxation time. We further explicitly compute, for the first time, the transport coefficients that couple the bulk viscous pressure to the shear-stress tensor and vice versa. The coefficient that couples bulk viscous pressure to shear-stress tensor is found to be orders of magnitude larger than the bulk viscosity itself, suggesting that bulk viscous pressure production owes more to this coupling than to the expansion rate of the system.

Driven by the Beam Energy Scan (BES) program at the RHIC, researches and discussions on the QCD phase diagram have flourished recently. In order to provide a reference from microscopic transport models, we performed a systematic analysis, using a multiphase transport (AMPT) model for the particle yields and a statistical model (thermus) for the thermal fit, for Au + Au collisions at $\sqrt{s_{\mathrm{NN}}}=7.7–200$ GeV. It is found that at a fixed collision centrality the chemical freeze-out parameter, temperature $T_{\mathrm{ch}}$, increases with collision energy and somehow saturates at certain values of $T_{\mathrm{ch}}$ in collisions near $\sqrt{s_{\mathrm{NN}}}=10$ GeV, indicating the limiting temperature in hadronic interactions; meanwhile the baryon chemical potential ${\mu }_B$ decrease with the collision energy. The saturation temperature is also found to be dependent on partonic interaction. At a given collision energy, it is found that both $T_{\mathrm{ch}}$ and ${\mu }_B$ decrease towards more peripheral collisions in the grand canonical approach. The energy and centrality dependence of other chemical freeze-out parameters, strangeness chemical potential ${\mu }_S$, strangeness undersaturation factor ${\gamma }_S$, and the volume of the fireball $V$ are also presented in this paper. The chemical potential ratio ${\mu }_s/{\mu }_B$ is also compared with lattice QCD calculation. The AMPT default model gives better descriptions on both the particle yields and the chemical freeze-out parameters than those from the AMPT string-melting model.

In this paper we investigate how the energy and momentum deposited by partonic dijets in the quark-gluon plasma (QGP) may affect the direct, elliptic, and triangular flow of low (and intermediate) $p_T$ hadrons in central $\mathrm{Au}+\mathrm{Au}$ collisions at the BNL Relativistic Heavy Ion Collider. The dijets are modeled as external sources in the energy-momentum conservation equations for hydrodynamics, which are solved on an event-by-event basis within the ideal-fluid approximation. We focus our investigation at midrapidity and solve the hydrodynamic equations by imposing boost invariance. Differential anisotropic flow coefficients for $p_T\gtrsim 1\mathrm{GeV}$ are found to be significantly enhanced if the dijets deposit on average more than 12 GeV in the QGP (or more than 6 GeV per jet). Because this extra energy and momentum added to the medium perturbs the geometry-induced hydrodynamic expansion, the correlation between the $v_2$ and $v_3$ coefficients (for $p_T\gtrsim 1\mathrm{GeV}$) and their corresponding initial eccentricities are considerably weakened. In addition, we argue that the extra amount of direct flow induced by dijets may be quantified by comparing the azimuthal dependence of dihadron correlations in dijet events with the corresponding quantity obtained in events without dijets. This comparison could be used to give a rough estimate of the magnitude of the effective coupling between the jets and the medium.

The quantum-fluctuation method using Coulomb corrections is explored to extract temperatures and densities of hot nuclear systems produced in Fermi-energy heavy-ion collisions. The role of the neutron-proton asymmetry of the system was investigated. Temperature values were observed to not depend on the system neutron-proton asymmetry while a clear dependence is seen for density values. Coulomb corrections have been shown to lower temperature values by almost 2 MeV. On the other hand, density results exhibit a small variation.