We introduce additional coalescence factors for the production of strange baryons in a multiphase transport (AMPT) model in order to describe the enhanced production of multistrange hadrons observed in $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$ at the Large Hadron Collider (LHC) and $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ at Relativistic Heavy-Ion Collider (RHIC). This extended AMPT model is found to also give a reasonable description of the multiplicity dependence of the strangeness enhancement observed in high multiplicity events in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ and $p$-Pb collisions at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. We find that the coalescence factors depend on the system size but not much on whether the system is produced from $\mathrm{A}+\mathrm{A}$ or $p+\mathrm{A}$ collisions. The extended AMPT model thus provides a convenient way to model the mechanism underlying the observed strangeness enhancement in collisions of both small and large systems at RHIC and LHC energies.

Comparison of hydrodynamic calculations with experimental data inevitably requires a model for converting the fluid to particles. For shear viscous fluids, several different conversion models have been proposed, such as the quadratic Grad corrections, the Strickland-Romatschke (SR) ansatz, self-consistent shear corrections from linearized kinetic theory, or corrections from the relaxation time approach. We show, via comparison to nonlinear $2\to 2$ kinetic theory evolution, that even for low specific shear viscosities $0.03\lesssim \eta /s\lesssim 0.2$, these four models have varying accuracy and still significant errors in reproducing particle phase space densities from hydrodynamic fields. Moreover, we demonstrate that the overall reconstruction error of additive shear viscous $f=f_{\mathrm{eq}}+\delta f$ models dramatically reduces by up to one order of magnitude, if one ensures through exponentiation that $f$ is always positive. We also illustrate how even more accurate viscous $\delta f$ models can be constructed by incorporating the first time derivatives of hydrodynamic fields to account for the past evolution of the system. Such time derivatives are readily available in hydrodynamic simulations, though usually not included in the output. Though our comparisons are limited to a one-component massless system undergoing a $(0+1)$-dimensional $(0+1\mathrm{D})$ longitudinal boost-invariant expansion, we expect that the improved models will be useful in $2+1\mathrm{D}$ and $3+1\mathrm{D}$ hydrodynamic studies as well.

The high-precision differential cross-section data for the reaction $\gamma p\to K^{*+}\mathrm{\Lambda }$ are reanalyzed within a Regge-inspired effective Lagrangian approach. The model adopts Regge phenomenology to constrain the $t$-channel contributions from the $\kappa$, $K$, and $K^{*}$ exchanges. A minimal number of resonances in the $s$ channel are introduced in constructing the reaction amplitudes in order to describe the data. It is shown that the differential cross-section data for $\gamma p\to K^{*+}\mathrm{\Lambda }$ can be satisfactorily described by introducing the only $N\left(2060\right){5/2}^{-}$ resonance in the $s$ channel, which is quite different from our earlier work performed in an effective Lagrangian approach [A. C. Wang et al., Phys. Rev. C 96, 035206 (2017)], where the amplitudes are computed by evaluating Feynman diagrams and it is found that introducing at least one additional resonance apart from the $N\left(2060\right){5/2}^{-}$ is indispensable for reproducing the data. The roles of individual contributions from meson and baryon exchanges on the angular distributions are found to be highly model dependent. The extracted mass of $N\left(2060\right){5/2}^{-}$ turns out to be well determined, independent of how the $t$-channel amplitudes are constructed, whereas the width does not.

The cross section of the ${}^{23}\mathrm{Na}(n,\gamma ){}^{24}\mathrm{Na}, {}^{41}\mathrm{K}(n,p){}^{41}\mathrm{Ar}, {}^{65}\mathrm{Cu}(n,p){}^{65}\mathrm{Ni}$, and ${}^{127}\mathrm{I}(n,2n){}^{126}\mathrm{I}$ reactions have been measured at $14.92\pm 0.02$ MeV neutron energy through neutron activation method followed by off-line $\gamma$-ray spectrometry. ${}^{27}\mathrm{Al}(n,\alpha ){}^{24}\mathrm{Na}$ is used as a reference reaction for the neutron flux normalization. The neutron beam was produced via the ${}^3\mathrm{H}(d,n)$ fusion reaction. Detailed uncertainty propagation has been performed using the covariance analysis and the measured cross sections are being reported with their uncertainties and correlation matrix. The cross sections measured in the present work are compared with the earlier reported cross sections available in the EXFOR database. Furthermore, theoretical calculations have been performed using the empire-3.2 and talys-1.9 codes with RIPL-3 parametrization, from reaction threshold to 20 MeV. The present experimental cross sections are also compared with the evaluated nuclear data from TENDL-2017, JENDL-4.0, and ENDF/B-VIII.0. In the case of $\left(n,\gamma \right)$ and $\left(n,2n\right)$ reactions, the comparison is also made with the IRDFF-1.05 evaluation.

Three-body calculations of the $I=\frac{1}{2}, J^{\pi }={\frac{1}{2}}^{+}$ state of $K\overline{K}N$ system were performed. Using separable potentials for two-body interactions in the Faddeev equation, different reaction processes for the $K\overline{K}N$ three-body system were studied. Within this method, the $\pi \mathrm{\Sigma }K$ and $\pi \eta N$ mass spectra were extracted. Different types of $\overline{K}N\text{−}\pi \mathrm{\Sigma }$ potentials based on phenomenological and chiral SU(3) approach were used and the dependence of the mass spectra on the $\overline{K}N$ model of interaction was studied. It was shown that the $\pi \mathrm{\Sigma }K$ and $\pi \eta N$ mass spectra could be a useful tool to study the properties of the $N^{*}$ resonance.

Background: The ${}^{24}\mathrm{Mg}(\alpha ,\gamma ){}^{28}\mathrm{Si}$ reaction influences the production of magnesium and silicon isotopes during carbon burning and is one of eight reaction rates found to significantly impact the shape of calculated x-ray burst light curves. The reaction rate is based on measured resonance strengths and known properties of levels in ${}^{28}\mathrm{Si}$.

Purpose: It is necessary to update the astrophysical reaction rate for ${}^{24}\mathrm{Mg}(\alpha ,\gamma ){}^{28}\mathrm{Si}$ incorporating recent modifications to the nuclear level data for ${}^{28}\mathrm{Si}$, and to determine if any additional as-yet unobserved resonances could contribute to the ${}^{24}\mathrm{Mg}(\alpha ,\gamma ){}^{28}\mathrm{Si}$ reaction rate.

Methods: The reaction rate has been recalculated incorporating updated level assignments from ${}^{28}\mathrm{Si}(\alpha ,{\alpha }^{\prime }){}^{28}\mathrm{Si}$ data using the ratesmc Monte Carlo code. Evidence from the ${}^{28}\mathrm{Si}(p,p^{\prime }){}^{28}\mathrm{Si}$ reaction suggests that there are no further known resonances which could increase the reaction rate at astrophysically important temperatures, though some resonances do not yet have measured resonance strengths.

Results: The reaction rate is substantially unchanged from previously calculated rates, especially at astrophysically important temperatures. However, the reaction rate is now constrained to better than 20% across the astrophysically relevant energy range, with 95% confidence. Calculations of the x-ray burst light curve show no appreciable variations when varying the reaction rate within the uncertainty from the Monte Carlo calculations.

Conclusion: The ${}^{24}\mathrm{Mg}(\alpha ,\gamma ){}^{28}\mathrm{Si}$ reaction rate, at temperatures relevant to carbon burning and Type I x-ray bursts, is well constrained by the available experimental data. This removes one reaction from the list of eight previously found to cause variations in x-ray burst light-curve calculations.

The form factor of the electromagnetic excitation of ${}^{12}\mathrm{C}$ to its $2_1^{+}$ state was measured at extremely low momentum transfers in an electron-scattering experiment at the Superconducting Darmstadt Electron Linear Accelerator (S-DALINAC). A combined analysis with the world form-factor data results in a reduced transition strength $B(E2;2_1^{+}\to 0_1^{+})=7.63\left(19\right)e^2{\mathrm{fm}}^4$ with an accuracy improved to 2.5%. In-medium no-core shell-model results with interactions derived from chiral effective field theory are able to reproduce the result. A quadrupole moment $Q\left(2_1^{+}\right)=5.97\left(30\right)e{\mathrm{fm}}^2$ can be extracted from the strict correlation with the $B\left(E2\right)$ strength emerging in the calculations.

We report on new $\gamma$-ray spectroscopy results from $\beta$ decays of ${}^{99}\mathrm{In}$ and ${}^{101}\mathrm{Sn}$. 30 new $\gamma$ rays were observed following the $\beta$ decay of ${}^{99}\mathrm{In}$, and inconsistencies in the literature with respect to the $\gamma$ rays following the $\beta$ decay of ${}^{101}\mathrm{Sn}$ were addressed with two confirmed cases and two new transitions. The experimental $\gamma$-ray energies, intensities, and coincidence relationships are discussed with shell model calculations, where theoretical $\beta$-decay branching ratios from the parent nuclei and $\gamma$-ray cascades of excited states from the daughter nuclei were combined to generate hypothetical $\beta \gamma$ spectra and $\beta \gamma \gamma$ coincidence matrices. The most intense $\beta$-delayed $\gamma$-ray branches in both ${}^{99}\mathrm{Cd}$ and ${}^{101}\mathrm{In}$ were well reproduced with this approach, and several $\gamma$ rays were assigned to new excited states based on their good agreement with shell model predictions.

When the density of a nuclear system is decreased, homogeneous states undergo the so-called Mott transition towards clusterized states, e.g., $\alpha$ clustering, both in nuclei and in nuclear matter. Here we investigate such a quantum phase transition (QPT) by using microscopic energy density functional calculations with with the relativistic and the Gogny approaches on the diluted ${}^{16}\mathrm{O}$ nucleus. The evolution of the corresponding single-particle spectrum under dilution is studied, and a Mott-like transition is predicted at about 1/3 of the saturation density. A complementary study of quartet condensation and the corresponding macroscopic QPT is undertaken in infinite matter.

In this paper we study patterns of nuclear charge radii from three perspectives. The first is based on the so-called $\delta R_{i\mathrm{n}-j\mathrm{p}}$ relations, the root-mean-square deviation of which was reported to be 0.0072 fm for nuclei with both neutron number $N$ and proton number $Z$ $\ge 8$, and are pointed out here to have actually a much smaller value, which is $\approx 0.003$ fm for most nuclei with $N\ge 28$ and $Z\ge 28$. The second and third perspectives are new relations proposed in this paper. One is called the $\delta R_{\mathrm{nn}}$ relation enlightened from the so-called “nonpairing” interaction $\delta V_{\mathrm{nn}}$ in studies of nuclear binding energies, and the other is a linear dependence of nuclear charge radii in terms of valence nucleon numbers. All these relations are very accurate in most regions, and sizable deviations from these relations could be used to shed light on structural evolutions such as phase transitions and shape coexistence. About 830 unknown nuclear charge radii are enclosed in our Supplemental Material in this paper, with theoretical uncertainty below 0.03 fm.

The LUX-ZEPLIN (LZ) experiment will enable a neutrinoless double $\beta$ decay search in parallel to the main science goal of discovering dark matter particle interactions. We report the expected LZ sensitivity to ${}^{136}\mathrm{Xe}$ neutrinoless double $\beta$ decay, taking advantage of the significant ($>600$ kg) ${}^{136}\mathrm{Xe}$ mass contained within the active volume of LZ without isotopic enrichment. After 1000 live-days, the median exclusion sensitivity to the half-life of ${}^{136}\mathrm{Xe}$ is projected to be $1.06\times {10}^{26}$ years (90% confidence level), similar to existing constraints. We also report the expected sensitivity of a possible subsequent dedicated exposure using 90% enrichment with ${}^{136}\mathrm{Xe}$ at $1.06\times {10}^{27}$ years.

We present our calculation of electromagnetic effects, induced by the spectator charge on Feynman-$x_F$ distributions of charged pions in peripheral $\mathrm{Pb}+\mathrm{Pb}$ collisions at CERN SPS energies, including realistic initial space-time-momentum conditions for pion emission. The calculation is performed in the framework of our simplified implementation of the fire-streak model, adapted to the production of both ${\pi }^{-}$ and ${\pi }^{+}$ mesons. Isospin effects are included to take into account the asymmetry in production of ${\pi }^{+}$ and ${\pi }^{-}$ at high rapidity. A comparison to a simpler model from the literature is made. We obtain a good description of the NA49 data on the $x_F$ and $p_T$ dependence of the ratio of cross sections ${\pi }^{+}/{\pi }^{-}$. The experimental data favors short times ($0.5<\tau <2$ fm/$c$) for fast pion creation in the local fire-streak rest frame. The possibility of the expansion of the spectators is considered in our calculation, and its influence on the electromagnetic effect observed for the ${\pi }^{+}/{\pi }^{-}$ ratio is discussed. In addition we discuss the relation between anisotropic flow and the electromagnetic distortion of ${\pi }^{+}/{\pi }^{-}$ ratios, and study the influence of transverse expansion of fire streaks as well as their vorticity on this distortion. In this latter study we find that inclusion of rotation of fire streaks in our model gives a satisfactory description of the rapidity dependence of pion directed flow. We conclude that our implementation of the fire-streak model, which properly describes the centrality dependence of ${\pi }^{-}$ rapidity spectra at CERN SPS energies, also provides a quantitative description of the electromagnetic effect on the ${\pi }^{+}/{\pi }^{-}$ ratio as a function of $x_F$.

Charmonium is a valuable probe in heavy-ion collisions to study the properties of the quark gluon plasma, and is also an interesting probe in small collision systems to study cold nuclear matter effects, which are also present in large collision systems. With the recent observations of collective behavior of produced particles in small system collisions, measurements of the modification of charmonium in small systems have become increasingly relevant. We present the results of $J/\psi$ measurements at forward and backward rapidity in various small collision systems, $p+p$, $p+\mathrm{Al}$, $p+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$, at $\sqrt{s_{{}_{NN}}}=200$ GeV. The results are presented in the form of the observable $R_{AB}$, the nuclear modification factor, a measure of the ratio of the $J/\psi$ invariant yield compared to the scaled yield in $p+p$ collisions. We examine the rapidity, transverse momentum, and collision centrality dependence of nuclear effects on $J/\psi$ production with different projectile sizes $p$ and ${}^3\mathrm{He}$, and different target sizes Al and Au. The modification is found to be strongly dependent on the target size, but to be very similar for $p+\mathrm{Au}$ and ${}^3\mathrm{He}+\mathrm{Au}$. However, for 0%–20% central collisions at backward rapidity, the modification factor for ${}^3\mathrm{He}+\mathrm{Au}$ is found to be smaller than that for $p+\mathrm{Au}$, with a mean fit to the ratio of $0.89\pm 0.03$(stat)$\pm 0.08$(syst), possibly indicating final state effects due to the larger projectile size.

Background: The near-equilibrium properties of a QCD plasma can be encoded into transport coefficients such as bulk and shear viscosity. In QCD, the ratio of these transport coefficients to entropy density, $\zeta /s$ and $\eta /s$, depends nontrivially on the plasma's temperature. This is unlike in conformal systems where they take constant values such as $\eta /s=1/\left(4\pi \right)$.

Purpose: In this work, we show that in a $(0+1)\mathrm{D}$ boost-invariant fluid with no transverse expansion, a temperature-dependent $\zeta /s\left(T\right)$ or $\eta /s\left(T\right)$ can be described by an equivalent effective viscosity ${〈\zeta /s〉}_{\text{eff}}$ or ${〈\eta /s〉}_{\text{eff}}$. This effective viscosity combines the actual temperature-dependent $\zeta /s\left(T\right)$ or $\eta /s\left(T\right)$ with the temperature profile of the fluid. We extend the concept of effective viscosity in systems with transverse expansion and discuss how effective viscosities can be used to identify families of $\zeta /s\left(T\right)$ and $\eta /s\left(T\right)$ that lead to similar hydrodynamic evolution.

Methods: The Navier-Stokes relativistic hydrodynamic equations are used to provide a first definition of effective viscosity, in $(0+1)\mathrm{D}$ and $(1+1)\mathrm{D}$. In the $(0+1)\mathrm{D}$ case, the analysis is extended to Israel-Stewart-type second-order hydrodynamics to clarify the effect of higher-order hydrodynamics corrections on the effective viscosity.

Results: In a boost-invariant fluid with no transverse expansion [$(0+1)\mathrm{D}$], the effective viscosity is expressed as a simple integral of $\zeta /s\left(T\right)$ or $\eta /s\left(T\right)$ over temperature, with a weight determined by the speed of sound of the fluid. The result is general for any equation of state with a moderate temperature dependence of the speed of sound, including the QCD equation of state. This definition of effective viscosity can be used to identify infinite families of $\zeta /s\left(T\right)$ or $\eta /s\left(T\right)$ that produce essentially indistinguishable temperature profiles. In a boost-invariant cylindrical system [$(1+1)\mathrm{D}$], a similar definition of effective viscosity is obtained in terms of characteristic trajectories in time and transverse direction. This leads to an infinite number of constraints on an infinite functional space for $\zeta /s\left(T\right)$ and $\eta /s\left(T\right)$. Realistic examples are presented by using a finite number of constraints on a finite functional space.

Conclusions: The definition of effective viscosity in a $(0+1)\mathrm{D}$ system clarifies how infinite families of $\zeta /s\left(T\right)$ and $\eta /s\left(T\right)$ can result in nearly identical hydrodynamic temperature profiles. By extending the study to a boost-invariant cylindrical [$(1+1)\mathrm{D}$] fluid, we identify an approximate but more general definition of effective viscosity that highlights the potential and limits of the concept of effective viscosity in fluids with limited symmetries.

Ultra-relativistic peripheral collisions of heavy ions at the CERN Large Hadron Collider (LHC) can produce copies of numbers of lepton pairs via the two-photon process. Since the energies of the heavy ions are so high, multipair production cross sections of the light leptons, especially electrons, are quite large so that it is possible to measure them experimentally. To calculate the multipair production probabilities, first, we should have an impact parameter dependence cross section. We have obtained a well-behaved impact parameter dependence cross section and by using the Monte Carlo methods, we have calculated multipair production cross sections of electrons and muons in Pb-Pb heavy-ion collisions at LHC energies. We have also used some experimental restrictions in our calculation to compare our findings with the experimental results.

Open heavy-flavor hadrons provide unique probes of the medium produced in ultrarelativistic heavy-ion collisions. Due to their increased mass relative to light-flavor hadrons, long lifetime, and early production in hard-scattering interactions, they provide access to the full evolution of the partonic medium formed in heavy-ion collisions. This paper reports two-dimensional (2D) angular correlations between neutral $D$ mesons and unidentified charged particles produced in minimum-bias $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$. $D^0$ and ${\overline{D}}^0$ mesons are reconstructed via their weak decay to $K^{\mp }{\pi }^{\pm }$ using the Heavy Flavor Tracker in the Solenoidal Tracker at RHIC experiment. Correlations on relative pseudorapidity and azimuth $(\mathrm{\Delta }\eta ,\mathrm{\Delta }\varphi )$ are presented for peripheral, midcentral, and central collisions with $D^0$ transverse momentum from $2–10\mathrm{GeV}/c$. Attention is focused on the 2D peaked correlation structure near the triggered $D^0$ meson, the near-side (NS) peak, which serves as a proxy for a charm-quark-containing jet. The correlated NS yield of charged particles per $D^0$ meson and the 2D widths of the NS peak increase significantly from peripheral to central collisions. These results are compared with similar correlations using unidentified charged particles, consisting primarily of light-flavor hadrons, at similar trigger particle momenta. Similar per-trigger yields and widths of the NS correlation peak are observed. The present results provide additional evidence that $D^0$ mesons undergo significant interactions with the medium formed in heavy-ion collision and show, for the first time, significant centrality evolution of the NS 2D peak in the correlations of particles associated with a heavy-flavor hadron produced in these collisions.

We report on the design and performance of a Mott polarimeter optimized for a nominal 5-MeV electron beam from the Continuous Electron Beam Accelerator Facility (CEBAF) injector. The rf time structure of this beam allows the use of time of flight in the scattered electron detection, making it possible to cleanly isolate those detected electrons that originate from the scattering foil, and resulting in measured scattering asymmetries which are exceptionally stable over a broad range of beam conditions, beam currents, and foil thicknesses. In two separate series of measurements from two different photocathode electron sources, we have measured the Mott scattering asymmetries produced by an approximately 86% transversely polarized electron beam incident on ten gold foils with nominal thicknesses between 50 and 1000 nm. The statistical uncertainty of the measured asymmetry from each foil is below 0.25%. Within this statistical precision, the measured asymmetry was unaffected by ±1-mm shifts in the beam position on the target foil, and by beam current changes and dead-time effects over a wide range of beam currents. The overall uncertainty of our beam polarization measurement, arising from the uncertainty in the value of the scattering asymmetry at zero foil thickness as determined from our fits to the measured asymmetries versus scattering foil thicknesses, the estimated systematic effects, and the (dominant) uncertainty from the calculation of the theoretical Sherman function, is 0.61%. A simulation of the polarimeter using geant4 has confirmed that double scattering in the target foil is the sole source of the dependence of the measured asymmetry on foil thickness, and gives a result for the asymmetry versus foil thickness in good agreement with both our measurements and a simple calculation. Future measurements at different beam energies and with target foils of different atomic numbers will seek to bound uncertainties from small effects such as radiative corrections to the calculation of the polarimeter analyzing power. A simultaneous high-precision measurement of the beam polarization with a different polarimeter, AESOP (Accurate Electron Spin Optical Polarimeter), under development at the University of Nebraska, clearly possible at the CEBAF accelerator, will allow a high-precision comparison of our measured asymmetries with theoretical calculations of the Mott analyzing power. Finally, the improved precision of the current Mott polarimeter along with similar improvements to other Jefferson Lab polarimeters warrants another precision comparison of all of these polarimeters when measuring a beam of the same polarization.

A microscopic calculation of half-lives for the recently observed ${}^{108}\mathrm{Xe}\to {}^{104}\mathrm{Te}\to {}^{100}\mathrm{Sn}\alpha$-decay chain is performed by using a self-consistent framework based on energy density functionals. The relativistic density functional DD-PC1 and a separable pairing interaction of finite range are used to compute axially symmetric deformation-energy surfaces of ${}^{104}\mathrm{Te}$ and ${}^{108}\mathrm{Xe}$ as functions of quadrupole, octupole, and hexadecupole collective coordinates. Dynamic least-action paths are determined that trace the $\alpha$-particle emission from the equilibrium deformation to the point of scission. The calculated half-lives, 197 ns for ${}^{104}\mathrm{Te}$ and $50\mu \mathrm{s}$ for ${}^{108}\mathrm{Xe}$, are compared with recent experimental values of the half-lives of superallowed $\alpha$ decay of ${}^{104}\mathrm{Te}$: $<18$ ns, and ${}^{108}\mathrm{Xe}$: ${58}_{-23}^{+106}\mu \mathrm{s}$.