The splitting of elliptic flow measured in different regions of the momentum space of produced hadrons has been recently studied in transport models and proposed as a sensitive probe of the angular momentum carried by the fireball produced in a relativistic heavy ion collision. The initial-state angular momentum also gives rise to rapidity-odd directed flow which has been measured. We consider a relativistic hydrodynamic framework with the initial matter distribution suitably calibrated to describe the observed directed flow and apply it to study the spilt in the elliptic flow. Our study suggests that the split in the elliptic flow is mostly driven by directed and triangular flows and may be used to constrain models of initial-state rapidity distribution of matter in the fireball.

A new precision half-life measurement of ${}^{13}\mathrm{N}$ has been conducted using the TwinSol $\beta$-counting station at the University of Notre Dame. The measured value of $t_{1/2}^{\mathrm{new}}=597.05\left(19\right)\mathrm{s}$ differs from the previous world value by about $2.8\sigma$. An evaluation of the ${}^{13}\mathrm{N}$ half-life results in a $t_{1/2}^{\mathrm{world}}=597.19\left(22\right)\mathrm{s}$. Updated standard model predictions for the Fermi to Gamow-Teller mixing ratio $\rho$ and its associated correlation parameters have been calculated using the new ${}^{13}\mathrm{N}$ world half-life in preparation for a future measurement of the mixing ratio. Finally, an ab initio no-core configuration interaction (NCCI) calculation for the $B\left(\mathrm{GT}\right)$ of this decay, carried out using the Daejeon16 interaction, has been performed, revealing the need for higher-order chiral corrections.

Background: Coherent $\pi {}^0$ photoproduction on heavy nuclei has been suggested as a reliable tool to infer neutron skin thicknesses. To this aim, various experiments have been performed, especially on ${}^{208}\mathrm{Pb}$.

Purpose: We analyze the sensitivity of that reaction process to the nucleonic density, and especially to the neutron skin thickness, for ${}^{12}\mathrm{C}$, ${}^{40}\mathrm{Ca}$, and ${}^{208}\mathrm{Pb}$, for which reliable data exist, and on ${}^{116,124}\mathrm{Sn}$, for which measurements have been performed in Mainz. We study also the role played by the ${\pi }^0$-nucleus final-state interaction.

Methods: A model of the reaction is developed at the impulse approximation considering either plane waves or distorted waves to describe the $\pi {}^0$-nucleus scattering in the outgoing channel.

Results: Our calculations are in good agreement with existing data, especially for ${}^{208}\mathrm{Pb}$. The sensitivity of the theoretical cross sections to the choice of the nucleonic density is small and below the experimental resolution.

Conclusions: Coherent $\pi {}^0$ photoproduction is mostly an isoscalar observable that bares no practical sensitivity to the neutron skin thickness. To infer that structure observable it should be coupled to other reaction measurements, such as electron scattering, or by comparing experiments performed on isotopes of the same chemical element.

The relation between the fourth-order symmetry energy $E_{\text{sym,4}}\left({\rho }_0\right)$ of nuclear matter at saturation density ${\rho }_0$ and its counterpart $a_{\text{sym,4}}\left(A\right)$ of finite nuclei in a semiempirical nuclear mass formula is revisited by considering the high-order isospin-dependent surface tension contribution to the latter. We derive the full expression of $a_{\text{sym,4}}\left(A\right)$, which includes explicitly the high-order isospin-dependent surface tension effects, and find that the value of $E_{\text{sym,4}}\left({\rho }_0\right)$ cannot be extracted from the measured $a_{\text{sym,4}}\left(A\right)$ before the high-order surface tension is well constrained. Our results imply that a large $a_{\text{sym,4}}\left(A\right)$ value of several MeV obtained from analyzing nuclear masses can nicely agree with the empirical constraint of $E_{\text{sym,4}}\left({\rho }_0\right)\lesssim 2$ MeV from mean-field models and does not necessarily lead to a large $E_{\text{sym,4}}\left({\rho }_0\right)$ value of $\approx 20$ MeV obtained previously without considering the high-order surface tension. Furthermore, we also give the expression for the sixth-order symmetry energy $a_{\text{sym,6}}\left(A\right)$ of finite nuclei, which involves more nuclear matter bulk parameters and the higher-order isospin-dependent surface tension.

We investigate the coalescence factors $B_2$ and $B_3$ at low collision energies ($\sqrt{s_{\mathrm{NN}}}<6$ GeV) with special focus on the HADES and RHIC-Beam Energy Scan (BES) experiments. It is shown that, in order to properly interpret the coalescence factors $B_A$, two important corrections are necessary: (I) $B_2$ has to be calculated using the proton $\times$ neutron yields in the denominator, instead of the square of the proton yield, and (II) the primordial proton (neutron) densities have to be used for the normalization and not the final-state (free) protons (neutrons). Both effects lead to a drastic reduction of $B_2$ and $B_3$ at low energies. This reduction decreases the discrepancy between the volumes extracted from Hanbury Brown–Twiss measurements and the volumes extracted from the coalescence factor ($V\propto 1/B_2$). While at HADES and low RHIC-BES energies these corrections are substantial, they become irrelevant above $\sqrt{s_{\mathrm{NN}}}>6$ GeV. The proposed correction method is model independent and is only based on the measurement of protons, clusters, and charged pions.

Two-particle correlation measurements projected onto two-dimensional, transverse rapidity coordinates $(y_{T1},y_{T2})$ provide an independent, orthogonal view of the multidimensional correlation distribution that is most often studied via angular projections. As such, these independent transverse projections allow access to manifestations of dynamical fluctuations in relativistic heavy-ion collisions that angular-correlation measurements may not be sensitive to. We report nonidentified charged-particle correlations for $\text{Au}+\text{Au}$ minimum-bias collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV taken by the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). Correlations are presented as two-dimensional functions of transverse rapidity for like-sign, unlike-sign, and all charged-particle pairs, as well as for particle pairs whose relative azimuthal angles lie on the near-side, the away-side, or at all relative azimuth. The correlations are constructed using charged particles with transverse momentum $p_T\ge 0.15$ $\mathrm{GeV}/c$, pseudorapidity from $-1$ to 1, and azimuthal angles from $-\pi$ to $\pi$. The significant correlation structures that are observed evolve smoothly with collision centrality. The major correlation features include a saddle shape plus a broad peak with maximum near $y_T\approx 3$, corresponding to $p_T\approx 1.5$ $\mathrm{GeV}/c$. The broad peak is observed in both like- and unlike-sign charge combinations and in near- and away-side relative azimuthal angles. The all-charge, all-azimuth correlation measurements are compared with the predictions of hijing and epos to provide theoretical context for these new measurements. The results indicate that the correlations for peripheral to mid-central collisions can be approximately described as a superposition of nucleon $+$ nucleon collisions with minimal effects from the quantum chromodynamics medium. Strong medium effects are indicated in mid- to most-central collisions.

In this work we address the question of how well the chiral crossover transition can be understood in terms of a noninteracting hadron resonance gas model. Using the latest results on the variation of hadron masses as a function of the pion mass from lattice quantum chromodynamics, we study the temperature dependence of the renormalized chiral condensate in $2+1$ flavor QCD. Furthermore, we suggest a better criterion to estimate of the pseudocritical temperature, which gives $T_c=161.2\pm 1.7$ MeV, which is much improved compared to all the earlier results within the hadron resonance gas model or chiral perturbation theory. For the curvature of the pseudocritical line we find ${\kappa }_2=0.0203\left(7\right)$, which is in very good agreement with continuum extrapolated lattice results.

The effects of the isovector scalar $\delta$-meson field on the properties of finite nuclei, infinite nuclear matter, and neutron stars are investigated within a relativistic mean field (RMF) model which includes nonlinear couplings. Several parameter sets (SRVs) are generated to asses the influence of the $\delta$ meson on the properties of neutron stars. These parametrizations correspond to different values of the coupling constant of the $\delta$ meson to nucleons, with remaining ones calibrated to yield finite nuclei and infinite nuclear matter properties consistent with the available experimental data. It is observed that, to fit the properties of finite nuclei and infinite nuclear matter, a stronger coupling between the isovector vector $\rho$ meson and nucleons is required in the presence of a $\delta$ field. Furthermore, the $\delta$ meson is found to affect the radius of the canonical neutron star significantly. The value of dimensionless tidal deformability, $\mathrm{\Lambda }$, for the canonical neutron star also satisfies the constraints from the waveform model analysis of the GW170817 binary neutron star merger event. A covariance analysis is performed to estimate the statistical uncertainties of the model parameters as well as correlations among the model parameters and different observables of interest.

Background: The properties of nuclei located in the region “south” of ${}^{208}\mathrm{Pb}$ are important for understanding the $r$-process nucleosynthesis. While some isomeric states and their spectroscopic properties have been investigated experimentally in neutron-rich Pb, Tl, and Hg isotopes recently, a large portion of the area still remains unreachable.

Purpose: We aim to study the properties of nuclei in the region south of ${}^{208}\mathrm{Pb}$, including the binding and excitation energies and electromagnetic properties, in order to predict unknown properties of these nuclei, such as isomerism, utilizing a theoretical model which describes the experimentally known properties precisely. We also address whether the $N=126$ shell closure is robust or not when the proton number decreases from ${}^{208}\mathrm{Pb}$.

Methods: We performed large-scale shell-model calculations with a new Hamiltonian suggested in the present work. The model space is taken as the 5 proton orbits within $50<Z⩽82$ and the 13 neutron orbits within $82<N⩽184$, and one-particle-one-hole excitation is allowed across the $N=126$ gap. The Hamiltonian is constructed by combining the existing Hamiltonians, KHHE (with adjustment of its proton-proton part) and KHPE, and the monopole-based universal interaction.

Results: The shell-model results well reproduce the experimentally observed binding energies and spectroscopic properties, such as isomerism, core excitation, and electromagnetic properties. Some possible isomeric states in neutron-rich Pb, Tl, and Hg isotopes are predicted with transition energies and half-lives. The $N=126$ shell gap is predicted to be robust from $Z=82$ down to 72 with minor reduction. We also examine the effective charges and the quenching of the $g$ factors suitable for this region by comparisons between observed and calculated electromagnetic properties.

Conclusions: A new Hamiltonian is constructed for nuclei in the region south of ${}^{208}\mathrm{Pb}$, mainly including Pb, Tl, Hg, Au, Pt, Ir, Os, Re, and W isotopes around $N=126$, and provides them reasonable descriptions on nuclear properties including binding energies, excitation energies, and electromagnetic properties through shell-model studies. The present Hamiltonian and discussions provide fruitful information for future measurements and theoretical investigations for nuclei in this region, especially those around the $N=126$ shell, including the recommended effective charges and $g$ factors, the predicted binding energies, isomeric states, and core-excited states.

For the last two decades, experimental information on nuclear level densities for about 60 different nuclei has been obtained on the basis of the Oslo method. While each of these measurements has been typically compared to one or a few level density models, a global study including all the measurements has been missing. The present study provides a systematic comparison between Oslo data and six global level density models for 42 nuclei for which $s$-wave resonance spacings are also available. We apply a coherent normalization procedure to the Oslo data for each of the six different models, all being treated on the same footing. Our quantitative analysis shows that the constant-temperature model presents the best global description of the Oslo data, closely followed by the mean-field plus combinatorial model and Hartree-Fock plus statistical model. Their accuracies are quite similar, so that it remains difficult to clearly favour one of these models. When considering energies above the threshold where the experimental level scheme is complete, all the six models are shown to lead to rather similar accuracies with respect to Oslo data. The recently proposed shape method can, in principle, improve the situation since it provides an absolute estimate of the excitation-energy dependence of the measured level densities. We show for the specific case of ${}^{112}\mathrm{Cd}$ that the shape method could exclude the Hartree-Fock plus statistical model. Such an analysis remains to be performed for the bulk of data for which the shape method can be applied to the Oslo measurements before drawing conclusions on the general quality of a given nuclear level density model.

A comparative study is made of the momentum-space structure of dineutrons in the Borromean nuclei ${}^{11}\mathrm{Li}$, ${}^6\mathrm{He}$, ${}^{22}\mathrm{C}$, and ${}^{19}\mathrm{B}$. The ground-state properties of these nuclei are well described by a three-body model using a newly constructed finite-range $nn$ interaction in momentum space. I clarify how the mean opening angle between momenta of valence neutrons and the opening-angle distribution reflect the two-neutron density of the Borromean nuclei. By indicating the similarities to the distributions for the correlation angle in the knockout-reaction experiments, I show that the angular correlations of halo neutrons can provide rich information for the characteristic structure of dineutrons in the Borromean nuclei.

Nuclei in the vicinity of the $N=Z$ line provide many sensitive probes of isospin symmetry. One example concerns the character and sequence of low-lying states of the $T=1/2$ mirror pair ${}^{71}\mathrm{Kr}$ and ${}^{71}\mathrm{Br}$ which has been under debate for several decades. In this paper we report a new measurement of the absolute $\beta$-branching to ground and excited states which, taken with our precise lifetime of $T_{1/2}=94.9\left(4\right)\text{ms}$, gives a superallowed ground state–to–ground state $\log (ft$) value of 3.64(4). This is only consistent with both ${}^{71}\mathrm{Br}$ and ${}^{71}\mathrm{Kr}$ having the same spin and parity, $J^{\pi }=5/2^{-}$, as expected from mirror symmetry. The $\beta$-delayed proton emission to the first-excited state in ${}^{70}\mathrm{Se}$ was observed for the first time which also strongly supports this assignment.

The excited states in ${}^{73}\mathrm{Br}$ nucleus have been investigated through the fusion evaporation reaction ${}^{50}\mathrm{Cr}({}^{28}\mathrm{Si}$, $\alpha p){}^{73}\mathrm{Br}$ at a beam energy of 90 MeV using the Indian National Gamma Array. The $\gamma \text{−}\gamma$ coincidence technique has been used to add eight new $\gamma$-ray transitions in the level scheme. The mixing ratio of $\mathrm{\Delta }I=0$ (mixed with $E2$ and $M1$) transitions have been determined using angular distribution and $R_{\mathrm{DCO}}$-polarization measurement. The half-life of the ${\mathrm{9/2}}^{+}$ isomeric state has been measured to be ${\tau }_{1/2}=52\left(2\right)$ ns from the variation in the intensity of delayed $\gamma$-ray transition as a function of coincidence time window. The two state mixing model calculations were performed to obtain the mixing amplitude, and mixing interaction of two different configurations of ${}^{73}\mathrm{Br}$. The calculated mixing amplitudes along with the deformations of two different configurations provide the monopole transition strength ${\rho }^2\left(E0\right)$ for Se, Br, and Kr isotopes in a semiempirical approach. These results support a prolate-oblate shape coexistence in the odd-$A{}^{73}\mathrm{Br}$ nucleus. The observed structural properties have been discussed in terms of projected shell model calculations.

The structure of ${}^{64}\mathrm{Ni}$, the heaviest stable Ni isotope, has been investigated via high-statistics, multistep safe Coulomb excitation to search for shape coexistence, a phenomenon recently observed in neutron-rich ${}^{66}\mathrm{Ni}$ and ${}^{70}\mathrm{Ni}$ as well as in doubly magic, $N=40, {}^{68}\mathrm{Ni}$. The study was motivated by recent, state-of-the-art Monte Carlo shell-model calculations (MCSM), where a Hamiltonian with effective interactions incorporating the monopole tensor force predicts the existence of shape coexistence, also in the lower-mass ${}^{62,64}\mathrm{Ni}$ isotopes. A set of transition and static $E2$ matrix elements for both yrast and near-yrast structures was extracted from the differential Coulomb excitation cross sections. From comparisons between the new results and MCSM as well as other shell-model calculations, a clearer picture of the structure of ${}^{64}\mathrm{Ni}$ emerges. Specifically, the low-spin states are shown to be dominated by proton and neutron excitations mainly within the $fp$ shell, with minimal contribution from the $g_{9/2}$ shape-driving neutron orbital. The agreement between experimental data and MCSM results indicates a small oblate deformation for the $0_2^{+}$ level and a spherical shape for the $0_3^{+}$ state. In addition, the small upper limit determined for the $B\left(E2\right)$ probability of a transition associated with the decay of the recently observed 3463-keV, $0_4^{+}$ state agrees with its proposed assignment to a prolate shape, herewith providing first evidence for triple shape coexistence in a stable Ni isotope.

A possible mechanism to explain the origin of the light $p$ nuclei in the Galaxy is the nucleosynthesis in the proton-rich neutrino-driven wind ejecta of core-collapse supernovas via the $\nu p$ process. However, this production scenario is very sensitive to the underlying supernova dynamics and the nuclear physics input. As far as the nuclear uncertainties are concerned, the breakout from the $pp$ chains via the ${}^7\mathrm{Be}(\alpha ,\gamma ){}^{11}\mathrm{C}$ reaction has been identified as an important link which can influence the nuclear flow and, therefore, the efficiency of the $\nu p$ process. However, its reaction rate is poorly known over the relevant temperature range, $T$ = 1.5–3 GK. We report on the first direct measurement of two resonances of the ${}^7\mathrm{Be}(\alpha ,\gamma ){}^{11}\mathrm{C}$ reaction with previously unknown strengths using an intense radioactive ${}^7\mathrm{Be}$ beam from the Isotope Separator and Accelerator (ISAC-I) Center facility and the DRAGON recoil separator in inverse kinematics. We have decreased the ${}^7\mathrm{Be}(\alpha ,\gamma ){}^{11}\mathrm{C}$ reaction rate uncertainty to $\approx 9.4\text{–}10.7$% over the relevant temperature region.

The $\beta$ decay of ${}^{76}\mathrm{Cu}$ to the levels of ${}^{76}\mathrm{Zn}$ was studied at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Lab (ORNL). A purified ${}^{76}\mathrm{Cu}$ beam was developed and data were recorded for the decay of the $A=76$ decay chain using four high-purity germanium (HPGe) clover detectors at the Low-energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS). In this measurement, data on γ-ray emission following $\beta$ decay, including $\beta \gamma$ and $\gamma \gamma$ coincidences, were collected and $\gamma \gamma$ spectra were analyzed to identify the statistically significant coincidences. From this analysis, we propose a level scheme for ${}^{76}\mathrm{Zn}$ which contains a total of 59 energy levels up to 6.0 MeV containing 105 $\gamma$ rays. We have identified an additional 53 $\gamma$ rays associated with this decay which could not be place in the decay scheme due to insufficient coincidence information or no energy match to identified levels. No $\gamma$ rays from states in ${}^{75}\mathrm{Zn}$ fed in the delayed-neutron branch were observed even though other $\gamma$ rays in the $A=75$ decay chain were observed. Spin and parity assignments are proposed for some levels based on comparison to systematics and shell model calculations.

Suppression of jet spectra or jet quenching in high-energy heavy-ion collisions is caused by jet energy loss in the dense medium. The azimuthal anisotropy of jet energy loss in noncentral heavy-ion collisions can lead to finite values of jet anisotropic flow coefficients. This is investigated within the linear Boltzmann transport model, which simulates both elastic scattering and medium-induced gluon radiation based on perturbative quantum chromodynamics for jet shower and medium recoil partons as well as radiated gluons as they propagate through the quark-gluon plasma. The dynamical evolution of the quark-gluon plasma in each event of heavy-ion collisions is provided by the $(3+1)$-dimensional CLVisc hydrodynamic model with fully fluctuating initial conditions. This framework has been shown to well describe the suppression of single inclusive jet spectra. We calculate in this study the elliptic $\left(v_2^{\mathrm{jet}}\right)$ and triangular $\left(v_3^{\mathrm{jet}}\right)$ anisotropy coefficients of the single inclusive jet spectra in $\text{Pb}+\text{Pb}$ collisions at the Large Hadron Collider energies. We investigate the colliding energy, centrality, jet transverse momentum dependence of the jet anisotropy, as well as their event-by-event correlation with the flow coefficients of the soft bulk hadrons. An approximate linear correlation between jet and bulk $v_2$ is found. The effect of the bulk $v_n$ fluctuation on $v_n^{\mathrm{jet}}$ is found negligible. We also investigate the effect of jet-induced medium excitation, which is influenced by radial flow, on jet $v_2^{\mathrm{jet}}$. The sensitivity of jet elliptic anisotropy $v_2^{\mathrm{jet}}$ to the shear viscosity of the bulk medium is also studied.

We propose to utilize the $K^{-}d\to {\pi }^{-}\mathrm{\Lambda }p$ and $K^{-}d\to {\pi }^0\mathrm{\Lambda }n$ reactions in order to investigate the difference between the low-energy $\mathrm{\Lambda }p$ and $\mathrm{\Lambda }n$ interactions. In these reactions, the $\mathrm{\Lambda }p$ and $\mathrm{\Lambda }n$ scatterings appear as final state interactions. We calculate the differential cross sections of these reactions with stopped kaons theoretically. We introduce isospin breaking by using the physical masses for the participating hadrons and through the chiral unitary amplitudes for $K^{-}N\to \pi N$ and $K^{-}N\to \overline{K}N$. With stopped kaons, the $\mathrm{\Lambda }N$ interaction takes place dominantly in the spin-triplet state thanks to the deuteron spin and $s$-wave dominance of the scattering amplitudes at low energy. We find that the ratio of the $\mathrm{\Lambda }N$ invariant mass spectra of these reactions is useful for revealing qualitative properties of charge symmetry breaking in the low-energy $\mathrm{\Lambda }N$ interaction. We also find that the contributions coming from the $\pi$ and $\mathrm{\Sigma }$ exchange diagrams which have $\pi N$ final state interaction and $\mathrm{\Sigma }N\to \mathrm{\Lambda }N$ conversion, respectively, are negligibly small around the $\mathrm{\Lambda }N$ threshold, while the contributions from the impulse diagram without final state interactions and the $\overline{K}$ exchange diagram containing the $\pi \mathrm{\Lambda }$ final state interaction are main sources of the background.

Energetic quarks liberated from hadrons in nuclear deep-inelastic scattering propagate through the nuclear medium, interacting with it via several processes. These include quark energy loss and nuclear interactions of forming hadrons. One manifestation of these interactions is the enhanced emission of low-energy charged particles, referred to as grey tracks. We use the theoretical components of the BeAGLE event generator to interpret grey track signatures of parton transport and hadron formation by comparing its predictions to E665 data. We extend the base version of BeAGLE by adding four different options for describing parton energy loss. The E665 data we used consists of multiplicity ratios for fixed-target scattering of 490 GeV muons on xenon normalized to deuterium as a function of the number of grey tracks. We compare multiplicity ratios for E665 grey tracks to the predictions of BeAGLE, varying the options and parameters to determine which physics phenomena can be identified by these data. We find that grey tracks are unaffected by modifications of the forward production. Thus their production must be dominated by interactions with hadrons in the backward region. This offers the advantage that selecting certain particles in the forward region is unlikely to bias a centrality selection. We see a strong correlation between the number of grey tracks and the in-medium path length. Our energy loss model does not reproduce the suppression observed in the projectile region. We see an underprediction of the proton production rate in backward kinematics, suggesting that a stronger source of interaction with the nuclear medium is needed for accurate modeling. These results lay an important foundation for future spectator tagging studies at both Jefferson Laboratory and at the Electron-Ion Collider, where neutron and proton grey track studies will be feasible down to very small momenta.

We found the important role of the spatially compact nucleon wave packets to fully describe the nucleon correlations within the framework of the high-momentum antisymmetrized molecular dynamics (HM-AMD), which is a variational method based on the antisymmetrized molecular dynamics. In HM-AMD, short-range and tensor correlations between nucleons are described by nucleon pairs with high momentum (high-momentum pairs), which are given by putting large centroids of the Gaussian wave packets in opposite signs. In this paper, we further improve momentum distribution of the high-momentum pairs by varying the width parameter of the Gaussian wave packets of nucleons. We show the reliability of this new scheme by applying it to the ${}^3\mathrm{H}$ nucleus with the bare Argonne v8' potential. It is found that the spatially compact nucleon wave packets give the important effect to lower the total energy, which brings sufficient high-momentum components in the nucleus. We also include the spin-parallel configuration of the three nucleons induced by the tensor interaction, which is necessary to converge the HM-AMD results. Finally, comparable results to the other theoretical calculations are obtained for the total energy and Hamiltonian components.