Pauli blocking is carefully investigated for the processes of $NN\leftrightarrow N\mathrm{\Delta }$ and $\mathrm{\Delta }\to N\pi$ in heavy-ion collisions, aiming at a more precise prediction of the ${\pi }^{-}/{\pi }^{+}$ ratio which is an important observable to constrain the high-density symmetry energy. We use the $\mathrm{AMD}+\mathrm{JAM}$ approach, which combines the antisymmetrized molecular dynamics for the time evolution of nucleons and the Jet AA Microscopic transport model to treat processes for $\mathrm{\Delta }$ resonances and pions. As is known in general transport-code simulations, it is difficult to treat Pauli blocking very precisely due to unphysical fluctuations and additional smearing of the phase-space distribution function, when Pauli blocking is treated in the standard method of JAM. We propose an improved method in $\mathrm{AMD}+\mathrm{JAM}$ to use the Wigner function precisely calculated in AMD as the blocking probability. Different Pauli blocking methods are compared in heavy-ion collisions of neutron-rich nuclei, ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$, at 270 MeV/nucleon. With the more accurate method, we find that Pauli blocking is stronger, in particular for the neutron in the final state in $NN\to N\mathrm{\Delta }$ and $\mathrm{\Delta }\to N\pi$, compared to the case with a proton in the final state. Consequently, the ${\pi }^{-}/{\pi }^{+}$ ratio becomes higher when the Pauli blocking is improved, the effect of which is found to be comparable to the sensitivity to the high-density symmetry energy.

We present an attempt to probe the underlying structure of the quark-gluon plasma (QGP) at high resolution, based on the extracted jet transport coefficient $\widehat{q}$. We argue that the exchanged momentum $k$ between the hard parton and the medium varies over a range of scales, and for $k\ge 1\mathrm{GeV},\widehat{q}$ can be expressed in terms of a parton distribution function (PDF). Because the mass of a QGP constituent is unknown, we define a scaling variable $x_N$ to represent the ratio of the parton momentum to the momentum of a self-contained section of the plasma which has a mass of 1 GeV. This scaling variable is used to parametrize the QGP-PDF. Calculations based on this reconstructed $\widehat{q}$ are compared to data sensitive to the hardcore of jets, i.e., the single hadron suppression in terms of the nuclear modification factor $R_{AA}$ and the azimuthal anisotropy parameter $v_2$ as a function of transverse momentum $p_{\mathrm{T}}$, centrality, and energy of the collision. It is demonstrated that the scale evolution of the QGP-PDF is responsible for the reduction in the normalization of $\widehat{q}$ between fits to the Relativistic Heavy-Ion Collider and the Large Hadron Collider data; a puzzle, first discovered by the JET Collaboration.

We present the first application of the basis light-front quantization method to a simple chiral model of the nucleon-pion system as a relativistic bound state for the physical proton. The light-front mass-squared matrix of the nucleon-pion system is obtained within a truncated basis. The mass and the corresponding light-front wave function (LFWF) of the proton are computed by numerical diagonalization of the resulting mass-squared matrix. With the boost-invariant LFWF, we calculate the probability density distribution of the pion's longitudinal momentum fraction and the Dirac form factor of the proton.

We calculate the leading-twist, helicity-independent generalized parton distributions (GPDs) of the proton, at finite skewness, in the Nambu–Jona-Lasinio (NJL) model of quantum chromodynamics (QCD). The NJL model reproduces low-energy characteristics of QCD, including dynamical chiral symmetry breaking (DCSB). The proton bound-state amplitude is solved for using the Faddeev equation in a quark-diquark approximation, including both dynamical scalar and axial vector diquarks. GPDs are calculated using a dressed nonlocal correlator, consistent with DCSB, which is obtained by solving a Bethe-Salpeter equation. The model and approximations used observe Lorentz covariance, and as a consequence the GPDs obey polynomiality sum rules. The electromagnetic and gravitational form factors are obtained from the GPDs. We find a $D$ term of $-1.08$ when the nonlocal correlator is properly dressed, and $0.85$ when the bare correlator is used instead, suggesting that within this framework proton stability requires the constituent quarks to be dressed consistently with DCSB. We also find that the anomalous gravitomagnetic moment vanishes, as required by Poincaré symmetry.

We developed a microscopic model for antikaon absorption on two nucleons in nuclear matter. The absorption is described within a meson-exchange picture and the primary $K^{-}N$ interaction strength is derived from state-of-the-art chiral coupled-channels meson-baryon interaction models. We took into account the medium modification of the $K^{-}N$ scattering amplitudes due to the Pauli correlations. We derived the $K^{-}NN$ as well as $K^{-}N$ optical potentials as functions of nuclear matter density including the real part of the $K^{-}NN$ potential. We calculated the $K^{-}$ single- and two-nucleon absorption fractions and branching ratios for various mesonic and nonmesonic channels. We confirmed the crucial role of in-medium effects in our calculations. Our results are in very good agreement with available experimental data from old bubble chamber experiments as well as with the latest results from the AMADEUS collaboration.

Published data on the emission of charged particles following nuclear muon capture are extremely limited. In addition to its interest as a probe of the nuclear response, these data are important for the design of some current searches for lepton flavor violation. This work presents momentum spectra of protons and deuterons following ${\mu }^{-}$ capture in aluminum. It is the first measurement of a muon capture process performed with a tracking spectrometer. A precision of better than 10% over the momentum range of 100–$190\text{MeV}/c$ for protons is obtained; for deuterons of 145–$250\text{MeV}/c$ the precision is better than 20%. The observed partial yield of protons with emission momenta above $80\text{MeV}/c$ (kinetic energy $3.4\text{MeV}$) is $0.0322\pm 0.0007\left(\text{stat}\right)\pm 0.0022\left(\text{syst}\right)$ per capture, and for deuterons above $130\text{MeV}/c$ $\left(4.5\text{MeV}\right)$ it is $0.0122\pm 0.0009\left(\text{stat}\right)\pm 0.0006\left(\text{syst}\right)$. Extrapolating to total yields gives $0.045\pm 0.001\left(\text{stat}\right)\pm 0.003\left(\text{syst}\right)\pm 0.001\left(\text{extrapolation}\right)$ per capture for protons and $0.018\pm 0.001\left(\text{stat}\right)\pm 0.001\left(\text{syst}\right)\pm 0.002\left(\text{extrapolation}\right)$ for deuterons, which are the most precise measurements of these quantities to date.

Simpson and Tostevin proposed that the width and shape of exclusive parallel momentum distributions of the $A-2$ residue in direct two-nucleon knockout reactions carry a measurable sensitivity to the nucleon single-particle configurations and their couplings within the wave functions of exotic nuclei. We report here on the first benchmarks and use of this new spectroscopic tool. Exclusive parallel momentum distributions for states in the neutron-deficient nuclei ${}^{22}\mathrm{Mg},{}^{23}\mathrm{Al}$, and ${}^{24}\mathrm{Si}$ populated in such direct two-neutron removal reactions were extracted and compared to predictions combining eikonal reaction theory and shell-model calculations. For the well-known ${}^{22}\mathrm{Mg}$ and ${}^{23}\mathrm{Al}$ nuclei, measurements and calculations were found to agree, supporting the dependence of the parallel momentum distribution width on the angular momentum composition of the shell-model two-neutron amplitudes. In ${}^{24}\mathrm{Si}$, a level at 3439(9) keV, of relevance for the important ${}^{23}\mathrm{Al}(p,\gamma ){}^{24}\mathrm{Si}$ astrophysical reaction rate, was confirmed to be the $2_2^{+}$ state, whereas the $4_1^{+}$ state, expected to be strongly populated in two-neutron knockout, was not observed. This puzzle is resolved by theoretical considerations of the Thomas-Ehrman shift, which also suggests that a previously reported 3471-keV state in ${}^{24}\mathrm{Si}$ is, in fact, the ($0_2^{+}$) level with one of the largest experimental mirror-energy shifts ever observed.

The possibility of the ${}^{14}\mathrm{C}$ cluster being a basic building block of medium-mass nuclei is discussed. Although $\alpha$ cluster structures have been widely discussed in the light $N\approx Z$ mass region, the neutron-to-proton ratio deviates from unity in the nuclei near $\beta$-stability line and in neutron-rich nuclei. Thus, more neutron-rich objects with $N>Z$ could become the building blocks of cluster structures in such nuclei. The ${}^{14}\mathrm{C}$ nucleus is strongly bound and can be regarded as such a candidate. In addition, the path to the lowest shell-model configuration at short relative distances is closed for the ${}^{14}\mathrm{C}+{}^{14}\mathrm{C}$ structure, contrary to the case of the ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ structure; this allows an appreciable separation distance between the ${}^{14}\mathrm{C}$ clusters. The recent development of the antisymmetrized quasicluster model (AQCM) allows us to utilize a $jj$-coupling shell-model wave function for each cluster in a simplified way. The AQCM results for the ${}^{14}\mathrm{C}+{}^{14}\mathrm{C}$ structure in ${}^{28}\mathrm{Mg}$ are compared with the ones of cranked relativistic mean field (CRMF) calculations. Although theoretical frameworks of these two models are quite different, they give similar results for the nucleonic densities and rotational properties of the structure under investigation. The existence of a linear chain three-${}^{14}\mathrm{C}$ cluster structure in ${}^{42}\mathrm{Ar}$ has also been predicted in AQCM. These results confirm the role of the ${}^{14}\mathrm{C}$ cluster as a possible building block of cluster structures in medium-mass nuclei.

The elliptic flow ($v_2$) event-by-event fluctuations in PbPb collisions at 5.02 TeV are analyzed within the $\mathrm{HYDJET}++$ model. Using the multiparticle, so-called $Q$-cumulant method, $v_2\left\{2\right\}$, $v_2\left\{4\right\}$, $v_2\left\{6\right\}$, and $v_2\left\{8\right\}$ are calculated and used to study their ratios and to construct skewness (${\gamma }_1^{\exp }$) as a measure of the asymmetry of the elliptic flow distribution. Additionally, in order to check if there is a hydrodynamics nature in the elliptic collectivity generated by the $\mathrm{HYDJET}++$ model, the ratio of $v_2\left\{6\right\}-v_2\left\{8\right\}$ and $v_2\left\{4\right\}-v_2\left\{6\right\}$ distributions is calculated. The analysis is performed as a function of the collision centrality. In order to check the $\mathrm{HYDJET}++$ model responses, the results of this analysis are compared to the corresponding experimental measurements from the ALICE, ATLAS, and CMS experiments. A rather good qualitative agreement is found.

Motivated by the historical detection of gravitational waves from GW170817, the neutron star and the neutron drop, i.e., a certain number of neutrons confined in an external field, are systematically investigated by ab initio calculations as well as the nonrelativistic and relativistic state-of-the-art density functional theories. Strong correlations are found among the neutron star tidal deformability, the neutron star radius, the root-mean-square radii of neutron drops, and the symmetry energies of nuclear matter at supra-saturation densities. For dense matter composed of nucleons only, these correlations, together with the upper limit on the tidal deformability extracted from GW170817, provides the constraints for the neutron star radii, the neutron drop radii, and the symmetry energy at twice saturation density as $R_{1.4M_{\odot }}⩽13.4\pm 0.2\mathrm{km},R_{\mathrm{nd}}⩽2.41\pm 0.10\mathrm{fm}$, and $E_{\mathrm{sym}}\left(2{\rho }_0\right)⩽60.7\pm 10.9\mathrm{MeV}$, respectively.

We reexamine the longstanding problem of the superfluid transition temperature $T_c$ in dilute neutron matter. It is well known that $T_c$ is strongly affected by medium polarization effects (screening), which modify the pairing interaction in the medium. We study these effects within the random-phase approximation (RPA). It turns out that the widely used Landau approximation is sufficient only at densities below about $0.002{\text{fm}}^{-3}$. At higher densities, the full RPA leads to stronger screening than the Landau approximation.

In this paper, we have calculated the $\alpha$-decay half-lives of superheavy nuclei with $106\le Z\le 126$ and a neutron number of $150\le N\le 200$ within proximity potentials and deformed-spherical Coulomb potentials by using $WS4$ $\alpha$-decay energy and the semiclassical Wentzel-Kramers-Brillouin approximation for penetration probability. Besides, we have included the preformation factor within the cluster-formation model. We have investigated magic numbers and submagic numbers in the mentioned region; with high probability, 162, 178, and 184 are predicted as neutron magic numbers. We also have confirmed that there is good agreement between our predicted half-lives and the ones obtained from semiempirical relationships such as Royer, VSS, UDL, and SemFIS2.

We calculate the $\mathrm{\Lambda }$-nucleon scattering phase shifts and mixing angles by applying time-ordered perturbation theory to the manifestly Lorentz-invariant formulation of SU(3) baryon chiral perturbation theory. Scattering amplitudes are obtained by solving the corresponding coupled-channel integral equations that have a milder ultraviolet behavior compared to their nonrelativistic analogs. This allows us to consider the removed cutoff limit in our leading-order calculations also in the ${}^{3}P_0$ and ${}^{3}P_1$ partial waves. We find that, in the framework we are using, at least some part of the higher-order contributions to the baryon-baryon potential in these channels needs to be treated nonperturbatively, and we demonstrate how this can be achieved in a way consistent with quantum field theoretical renormalization for the leading contact interactions. We compare our results with the ones of the nonrelativistic approach and lattice QCD phase shifts obtained for non-physical pion masses.

We propose a new model to describe the $\alpha +\alpha$ interaction that takes into account the Pauli nonlocality through a velocity-dependent term. With this interaction, we describe very well the phase shifts obtained from elastic scattering data analyses for $\alpha +\alpha$ at low energies. We also obtain a good description of the $s$-wave resonance related to the ${}^8\mathrm{Be}$ ground-state. The model is based on double-folding procedures and, therefore, it can easily be extended to other systems. We present a test of the model in the case of elastic scattering for ${}^4\mathrm{He}+{}^{208}\mathrm{Pb}$.

Background: Clustering plays an important role in the structure of ${}^{10}\mathrm{Be}$. Exotic molecular-like configurations, such as $\alpha$:$2n$:$\alpha$, have been suggested at relatively low excitation energies.

Purpose: To search for the high-spin states that may belong to the molecular-like $\alpha$:$2n$:$\alpha$ configuration in ${}^{10}\mathrm{Be}$.

Method: Measuring excitation functions for ${}^6\mathrm{He}+\alpha$ scattering, populating states in the excitation energy range from 4.5 MeV to 8 MeV in ${}^{10}\mathrm{Be}$ using a ${}^6\mathrm{He}$ rare-isotope beam and a thick helium gas target.

Results: No new excited states in ${}^{10}\mathrm{Be}$ have been observed. Stringent limits on the possible degree of $\alpha$-clustering of the hypothetical yrast $6^{+}$ state have been obtained.

Conclusions: The high-spin members of the $\alpha$:$2n$:$\alpha$ molecular-like rotational band configuration, that is considered to have a $0^{+}$ band head at 6.18 MeV, either do not exist or have small overlap with the ${}^6\mathrm{He}$(g.s.)$+\alpha$ channel.

Isoscaling parameters $\alpha$ and $\beta$ have been explored as a function of breakup angle in binary excited projectile-like fragment decays produced in collisions of ${}^{70}\mathrm{Zn}+{}^{70}\mathrm{Zn}$ and ${}^{64}\mathrm{Zn}+{}^{64}\mathrm{Zn}$ at 35 MeV per nucleon. In this analysis, focus was placed on isoscaling the second heaviest fragment with $4\le Z_L\le 8$ emitted from the excited projectile-like fragment in events that contained a heavy fragment with $Z_H\ge 12$. The breakup orientation ${\theta }_{\mathrm{prox}}$ was defined as the angle between the heavy and light fragments' center-of-mass velocity and the fragment pairs' relative velocity. Breakups between $0^{\circ }<{\theta }_{\mathrm{prox}}\le {80}^{\circ }$ have been shown to be dominated by dynamical contributions, while break-up angles of ${\theta }_{\mathrm{prox}}>{100}^{\circ }$ are predominantly statistical. Historically, isoscaling has often been understood and applied in a statistical context, assuming that the fragments are produced after statistical equilibrium is achieved. Studying isoscaling parameters as a function of ${\theta }_{\mathrm{prox}}$ reveals the sensitivity of $\alpha$ and $\beta$ to the mechanism of fragment production.

The thermodynamic properties of high temperature and high density QCD matter are explored within the chiral SU(3)-flavor parity-doublet Polyakov-loop quark-hadron mean-field model, CMF. The quark sector of the CMF model is tuned to describe the ${\mu }_B=0$ thermodynamics data of lattice QCD. The resulting lines of constant physical variables as well as the baryon number susceptibilities are studied in some detail in the temperature–chemical-potential plane. The CMF model predicts three consecutive transitions: the nuclear first-order liquid-vapor phase transition, chiral symmetry restoration, and the crossover transition to a quark matter phase. All three phenomena are crossovers, for most of the $T\text{−}{\mu }_B$ plane. The deviations from the free ideal hadron gas baseline at ${\mu }_B=0$ and $T\approx 100\text{–}200$ MeV can be attributed to remnants of the liquid-vapor first-order phase transition in nuclear matter. The chiral crossing transition determines the baryon fluctuations at much higher ${\mu }_B\approx 1.5$ GeV. At high baryon densities, ${\mu }_B\approx 2.4$ GeV, the behavior of fluctuations is controlled by crossover to quark matter. The CMF model also describe well the static properties of high ${\mu }_B$ neutron stars as well as recent neutron star merger observations. The effective equation of state presented here describes simultaneously lattice QCD results at ${\mu }_B=0$ as well as observed physical phenomena (nuclear matter and neutron star matter) at $T\cong 0$ and high densities, ${\mu }_B>1$ GeV.

Recently we updated a multiphase transport (ampt) model with modern parton distribution functions of nuclei (nPDFs). Here we study open charm production in the updated ampt model and compare to the experimental data from $pp$ and $AA$ collisions over a wide range of collision energies. Besides the update of nPDFs, we removed the transverse momentum cutoff on initial heavy quark productions and also included the resultant heavy flavor cross section into the total minijet cross section in the initial condition as described by the hijing model. We show that the ampt model with these updates provides a much better description of the yields and transverse momentum spectra of various open charm hadrons in comparison with the experimental data. This lays the foundation for further heavy flavor studies within the transport model approach.

A system size scan program was recently proposed for the STAR experiments at the Relativistic Heavy Ion Collider (RHIC). In this study, we employ a multiphase transport (ampt) model for considering the bulk properties at the freeze-out stage for ${}^{10}\mathrm{B}+{}^{10}\mathrm{B}$, ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$, ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}$, ${}^{20}\mathrm{Ne}+{}^{20}\mathrm{Ne}$, ${}^{40}\mathrm{Ca}+{}^{40}\mathrm{Ca}$, ${}^{96}\mathrm{Zr}+{}^{96}\mathrm{Zr}$, and ${}^{197}\mathrm{Au}+{}^{197}\mathrm{Au}$ collisions at RHIC energies $\sqrt{s_{NN}}$ of 200, 20, and 7.7 GeV. The results for ${}^{197}\mathrm{Au}+{}^{197}\mathrm{Au}$ collisions are comparable with those of previous experimental STAR data. The transverse momentum $p_T$ spectra of charged particles (${\pi }^{\pm }$, $K^{\pm }$, $p$, and $\overline{p}$) at the kinetic freeze-out stage, based on a blast-wave model, are also discussed. In addition, we use a statistical thermal model to extract the parameters at the chemical freeze-out stage, which agree with those from other thermal model calculations. It was found that there is a competitive relationship between the kinetic freeze-out parameter $T_{\mathrm{kin}}$ and the radial expansion velocity ${\beta }_T$, which also agrees with the STAR or ALICE results. We found that the chemical freeze-out strangeness potential ${\mu }_s$ remains constant in all collision systems and that the fireball radius $R$ is dominated by $〈N_{\mathrm{Part}}〉$, which can be well fitted by a function of $a{〈N_{\mathrm{Part}}〉}^b$ with $b\approx 1/3$. In addition, we calculated the nuclear modification factors for different collision systems with respect to the ${}^{10}\mathrm{B}+{}^{10}\mathrm{B}$ system, and found that they present a gradual suppression within a higher $p_T$ range from small to large systems.

We review the design, simulation, and tests of a detection system for measuring the energy distribution of daughter nuclei recoiling from the $\beta$ decay of laser trapped neon isotopes. This distribution is sensitive to several new physics effects in the weak sector. Our “decay microscope” relies on imaging the velocity distribution of high-energy recoil ions in coincidence with electrons shaken off in the decay. We demonstrate by way of Monte Carlo simulation that the nuclear microscope increases the statistical sensitivity of kinematic measurements to the underlying energy distribution and limits the main systematic bias caused by discrepancy in the trap position along the detection axis.