We present STAR measurements of strange hadron (${\mathrm{K}}_S^0, \mathrm{\Lambda }, \overline{\mathrm{\Lambda }}, {\mathrm{\Xi }}^{-}, {\overline{\mathrm{\Xi }}}^{+}, {\mathrm{\Omega }}^{-}, {\overline{\mathrm{\Omega }}}^{+}$, and $\varphi$) production at midrapidity ($\left|y\right|<0.5$) in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{{}_{NN}}}$ = 7.7–39 GeV from the Beam Energy Scan Program at the Relativistic Heavy Ion Collider (RHIC). Transverse-momentum spectra, averaged transverse mass, and the overall integrated yields of these strange hadrons are presented versus the centrality and collision energy. Antibaryon-to-baryon ratios ($\overline{\mathrm{\Lambda }}/\mathrm{\Lambda }, {\overline{\mathrm{\Xi }}}^{+}/{\mathrm{\Xi }}^{-}, {\overline{\mathrm{\Omega }}}^{+}/{\mathrm{\Omega }}^{-}$) are presented as well and used to test a thermal statistical model and to extract the temperature normalized strangeness and baryon chemical potentials at hadronic freeze-out (${\mu }_B/T_{\mathrm{ch}}$ and ${\mu }_S/T_{\mathrm{ch}}$) in central collisions. Strange baryon-to-pion ratios are compared to various model predictions in central collisions for all energies. The nuclear modification factors ($R_{\text{CP}}$) and antibaryon-to-meson ratios as a function of transverse momentum are presented for all collision energies. The ${\mathrm{K}}_S^0 R_{\text{CP}}$ shows no suppression for $p_T$ up to 3.5 $\mathrm{GeV}/c$ at energies of 7.7 and 11.5 GeV. The $\overline{\mathrm{\Lambda }}/{\mathrm{K}}_S^0$ ratio also shows baryon-to-meson enhancement at intermediate $p_T$ ($\approx 2.5 \mathrm{GeV}/c$) in central collisions at energies above 19.6 GeV. Both observations suggest that there is likely a change of the underlying strange quark dynamics at collision energies below 19.6 GeV.

We use the finite-amplitude method (FAM), an efficient implementation of the quasiparticle random phase approximation, to compute $\beta$-decay rates with Skyrme energy-density functionals for 3983 nuclei, essentially all the medium-mass and heavy isotopes on the neutron-rich side of stability. We employ an extension of the FAM that treats odd-mass and odd-odd nuclear ground states in the equal filling approximation. Our rates are in reasonable agreement both with experimental data where available and with rates from other global calculations.

In the shell-model framework, valence-space Hamiltonians connecting multiple major-oscillator shells are of key interest for investigating the physics of neutron-rich nuclei, which have been the subject of intense experimental activity for decades. Here we present an extension of the ab initio valence-space in-medium similarity renormalization group, which allows the derivation of such Hamiltonians nonperturbatively. Starting from initial two- and three-nucleon forces from chiral effective field theory, we then calculate properties of nuclei in the important island-of-inversion region above oxygen, so far unexplored with ab initio methods. Our results in the neon and magnesium isotopes indicate the importance of neutron excitation from the $sd$ to $pf$ shells and ground states dominated by intruder configurations around $N=20$, consistent with the conclusions from phenomenological studies. We also benchmark the excitation spectrum of ${}^{16}\mathrm{O}$ with coupled-cluster theory, finding generally good agreement, and discuss implications for ground-state energies and charge radii in oxygen and calcium isotopes. Finally we outline the proper procedure for treating the longstanding issue of center-of-mass contamination, and show that with a particular choice of valence space, these spurious states can be removed successfully.

We propose observables $v_0$ and $v_0\left(p_T\right)$ which quantify the relative fluctuations in the total transverse momentum at fixed multiplicity. We first study the factorization of the fixed multiplicity momentum-dependent two-particle correlation function into a product of $v_0\left(p_T^a\right)$ and $v_0\left(p_T^b\right)$ within realistic hydrodynamic simulations. Then we present computations of $v_0\left(p_T\right)$ for different particle types. We determine the relation between the integrated $v_0$ and previously measured observables and compare results from a hybrid hydrodynamics-based model to experimental data. The effects of bulk viscosity and an initial pre-equilibrium stage on the results are quantified. We find that $v_0$ is strongly correlated with the initial state entropy per elliptic area, $S/A$. Using this result, we explain how the observed correlations between the elliptic flow and the transverse momentum (both in simulations and experiment) reflect the initial state correlations between $1/A$ and ellipticity ${\varepsilon }_2$ at fixed multiplicity. We argue that the systematic experimental study of $v_0$, with the same sophistication as used for the other $v_n$, can contribute significantly to our understanding of quark gluon plasma properties.

We present an analysis of proton-number fluctuations in $\sqrt{s_{NN}}=2.4 \mathrm{GeV}$ ${}^{197}\mathrm{Au}+{}^{197}\mathrm{Au}$ collisions measured with the High-Acceptance DiElectron Spectrometer (HADES) at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. With the help of extensive detector simulations done with Isospin Quantum Molecular Dynamics (IQMD) transport model events including nuclear clusters, various nuisance effects influencing the observed proton cumulants have been investigated. Acceptance and efficiency corrections have been applied as a function of fine-grained rapidity and transverse momentum bins, as well as considering local track density dependencies. Next, the effects of volume changes within particular centrality selections have been considered and beyond-leading-order corrections have been applied to the data. The efficiency and volume-corrected proton number moments and cumulants $K_n$ of orders $n=1, 2, 3, \mathrm{and} 4$ have been obtained as a function of centrality and phase-space bin, as well as the corresponding correlators $C_n$. We find that the observed correlators show a power-law scaling with the mean number of protons, i.e., $C_n\propto {\langle N\rangle }^n$, indicative of mostly long-range multiparticle correlations in momentum space. We also present a comparison of our results with Au $+$ Au collision data obtained at the Relativistic Heavy Ion Collider (RHIC) at similar centralities but higher $\sqrt{s_{NN}}$.

We report quantum Monte Carlo calculations of weak transitions in $A\le 10$ nuclei, based on the Norfolk two- and three-nucleon chiral interactions, and associated one- and two-body axial currents. We find that the contribution from two-body currents is at the 2–3% level, with the exception of matrix elements entering the rates of ${}^8\mathrm{Li}$, ${}^8\mathrm{B}$, and ${}^8\mathrm{He}$ $\beta$ decay. These matrix elements are suppressed in impulse approximation based on the (leading order) Gamow Teller transition operator alone; two-body currents provide a $20–30\%$ correction, which is, however, insufficient to bring theory in agreement with experimental data. For the other transitions, the agreement with the data is satisfactory, and the results exhibit a negligible to mild model dependence when different combinations of Norfolk interactions are utilized to construct the nuclear wave functions. We report a complete study of two-body weak transition densities which reveals the expected universal behavior of two-body currents at short distances throughout the range of $A=3$ to $A=10$ systems considered here.

Relativistic quantum molecular dynamics based on the relativistic mean field theory (RQMD.RMF) is extended by including momentum-dependent potential. The equation of state (EoS) dependence of the directed and the elliptic flow of protons in the beam energy range of $2.3<\sqrt{s_{NN}}<20$ GeV is examined. It is found that the directed flow depends strongly on the optical potential at high energies, $\sqrt{s_{NN}}>3$ GeV, where no information is available experimentally. The correlation between effective mass at saturation density and the optical potential is found: smaller values of effective mass require smaller strengths of the optical potential to describe the directed flow data. This correlation can also be seen in the beam energy dependence of the elliptic flow at $\sqrt{s_{NN}}>3$ GeV, although its effect is rather weak. On the other hand, stiff EoS is required to describe the elliptic flow at lower energies. Experimental constraints on the optical potential from $pA$ collisions will provide important information on the EoS at high energies. The proton directed and the elliptic flow are well described in the RQMD.RMF model from $\sqrt{s_{NN}}=2.3$ to 8.8 GeV. In contrast, to reproduce the collapse of the directed flow above 10 GeV, pressure has to be reduced, which indicates a softening of the EoS around $\sqrt{s_{NN}}=10$ GeV.

The nonrelativistic reduction of the self-consistent covariant density functional theory is realized for the first time with the similarity renormalization group method. The reduced nonrelativistic Hamiltonian and densities are calculated by solving the corresponding flow equations with a novel expansion in terms of the inverse of the Dirac effective mass. The efficiency and accuracy of this newly proposed framework have been demonstrated for several typical spherical nuclei. It is found that the exact solutions of the total energies, traces of vector and scalar densities, and the root-mean-square radii are reproduced quite well for all nuclei. This allows one to directly compare and bridge the relativistic and nonrelativistic nuclear energy density functional theories in the future.

Transfer reactions provide information about the single-particle nature of nuclear levels. In particular, the differential cross sections from these measurements are sensitive to the angular momentum of the transferred particle and the spectroscopic factor of the populated level. However, the process of extracting these properties is subject to uncertainties, both from experimental and theoretical sources. By integrating the distorted wave Born approximation into a Bayesian model, we propagate these uncertainties through to the spectroscopic factors and orbital angular momentum values. We use previously reported data of the proton pickup reaction ${}^{70}\mathrm{Zn}(d,{}^{3}He){}^{69}\mathrm{Cu}$ as an example. By accounting for uncertainties in the experimental data, optical model parameters, and reaction mechanism, we find that the extracted spectroscopic factors for low-lying states of ${}^{69}\mathrm{Cu}$ are subject to large, asymmetric uncertainties ranging from 35 to $108\%$. Additionally, Bayesian model comparison is employed to assign probabilities to each of the allowed angular momentum transfers. This method confirms the assignments for many states, but suggests that the data for a state lying at 3.70 MeV are better characterized by an $\ell =3$ transfer, rather than the previously reported $\ell =2$.

The overlap in the mass symmetric region of the reaction products from fusion-fission and quasifission complicates the assignment of symmetric events to complete fusion on the basis of the mass distribution alone. Additional observables, besides mass distribution, should be used. The approach proposed here relies on the fact that fusion-fission and quasifission are characterized by different timescales. Within this framework, we performed a detailed study to find out how timescales can be probed via angular momentum transfer as measured via $\gamma$-ray multiplicities. The proof of principle was carried out by measuring the $\gamma$ rays in coincidence with fusion-fission and quasielastic binary fragments in the reaction ${}^{32}\mathrm{S}$ $+$ ${}^{197}\mathrm{Au}$ at beam energy near the Coulomb barrier. The experiment was performed at the Accélérateur Linéaire Tandem à Orsay (ALTO) facility at the Institut De Physique Nucléaire (IPN) in Orsay (France) using a detection setup consisting of ORGAM (ORsay GAMma) and PARIS (Photon Array Radioactive Ion Stable beams) $\gamma$-detectors arrays coupled with the CORSET (CORrelation SETup) time-of-flight spectrometer. Results of the sensitivity of this method to distinguish reaction channels with different dynamics are discussed.

We report on a precise measurement of the electron-antineutrino angular correlation ($a$ coefficient) in free neutron beta decay from the $a\mathrm{SPECT}$ experiment. The $a$ coefficient is inferred from the recoil energy spectrum of the protons which are detected in $4\pi$ by the $a\mathrm{SPECT}$ spectrometer using magnetic adiabatic collimation with an electrostatic filter. Data are presented from a 100-day run at the Institut Laue Langevin in 2013. The sources of systematic errors are considered and included in the final result. We obtain $a=-0.10430\left(84\right)$ which is the most precise measurement of the neutron $a$ coefficient to date. From this, the ratio of axial vector to vector coupling constants is derived giving $\left|\lambda \right|=1.2677\left(28\right)$.

Midrapidity production of ${\pi }^{\pm }, K^{\pm }$, and $\left(\overline{p}\right)p$ measured by the ALICE experiment at the CERN Large Hadron Collider, in Pb-Pb and inelastic $pp$ collisions at $\sqrt{s_{NN}}=5.02$ TeV, is presented. The invariant yields are measured over a wide transverse momentum ($p_{\mathrm{T}}$) range from hundreds of $\mathrm{MeV}/c$ up to 20 $\mathrm{GeV}/c$. The results in Pb-Pb collisions are presented as a function of the collision centrality, in the range $0–90\%$. The comparison of the $p_{\mathrm{T}}$-integrated particle ratios, i.e., proton-to-pion ($p/\pi$) and kaon-to-pion ($K/\pi$) ratios, with similar measurements in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV show no significant energy dependence. Blast-wave fits of the $p_{\mathrm{T}}$ spectra indicate that in the most central collisions radial flow is slightly larger at 5.02 TeV with respect to 2.76 TeV. Particle ratios ($p/\pi , K/\pi$) as a function of $p_{\mathrm{T}}$ show pronounced maxima at $p_{\mathrm{T}}\approx 3\mathrm{GeV}/c$ in central Pb-Pb collisions. At high $p_{\mathrm{T}}$, particle ratios at 5.02 TeV are similar to those measured in $pp$ collisions at the same energy and in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV. Using the pp reference spectra measured at the same collision energy of 5.02 TeV, the nuclear modification factors for the different particle species are derived. Within uncertainties, the nuclear modification factor is particle species independent for high $p_{\mathrm{T}}$ and compatible with measurements at $\sqrt{s_{NN}}=2.76$ TeV. The results are compared to state-of-the-art model calculations, which are found to describe the observed trends satisfactorily.

Background: Neutron-rich nuclei with mass number between 100 and 110 attract much attention, since several kinds of shapes, such as spherical, prolate, oblate, and triaxial shapes, are predicted. In particular, for neutron-rich Mo isotopes, different models predict different magnitudes and rigidity of triaxial deformation. Previous interpretations of experimental results based solely on low-lying $2_2^{+}$ states are insufficient to distinguish between the rigid triaxial shape, $\gamma$ vibration, or $\gamma$-soft rotor.

Purpose: The shape evolution of ${}^{106}\mathrm{Mo}$, ${}^{108}\mathrm{Mo}$, and ${}^{110}\mathrm{Mo}$ is investigated through their $2_1^{+}$-state lifetimes, decay-branching ratios of the $2_2^{+}$ state, and energies of the low-lying collective excited states with $K^{\pi }=0^{+},2^{+}$, and $4^{+}$.

Method: $\beta$-delayed $\gamma$-ray spectroscopy was employed for neutron-rich Nb and Zr isotopes produced at the RIKEN RI Beam Factory to populate excited states in ${}^{106}\mathrm{Mo}$, ${}^{108}\mathrm{Mo}$, and ${}^{110}\mathrm{Mo}$. The EUroball-RIKEN Cluster Array was used for high-resolution $\gamma$-ray detection and lifetimes of the $2_1^{+}$ states were determined using the UK fast-timing array of ${\mathrm{LaBr}}_3\left(\mathrm{Ce}\right)$ detectors.

Results: New $\gamma$-ray transitions and levels are reported, including newly assigned $0_2^{+}$ states in ${}^{108,110}\mathrm{Mo}$. Quadrupole deformations were obtained for ${}^{106,108,110}\mathrm{Mo}$ from their $2_1^{+}$ energies and lifetimes. The $\beta$-delayed neutron-emission probabilities of ${}^{108}\mathrm{Nb}$ and ${}^{110}\mathrm{Nb}$ were determined by examining the $\gamma$ rays of their respective daughter decays.

Conclusions: The even-odd energy staggering in the $2_2^{+}$ band was compared with typical patterns of the $\gamma$-vibrational band, rigid triaxial rotor, and $\gamma$-soft rotor. The very small even-odd staggering of ${}^{106}\mathrm{Mo}$, ${}^{108}\mathrm{Mo}$, and ${}^{110}\mathrm{Mo}$ favors a $\gamma$-vibrational band assignment. The kinematic moment of inertia for the $2_2^{+}$ band showed a trend similar to the ground-state band, which is as expected for the $\gamma$-vibrational band. Beyond-mean-field calculations employing the constrained Hartree-Fock-Bogoliubov and local quasiparticle-random-phase approximation method using the $\mathrm{SLy}5+\mathrm{T}$ interaction reproduced the ground and $2_2^{+}$ bands in ${}^{106}\mathrm{Mo}$ and ${}^{108}\mathrm{Mo}$. The collective wave functions are consistent with the interpretation of the $2_2^{+}$ band as the $\gamma$-vibrational band of the prolate shape. However, the staggering pattern observed in ${}^{110}\mathrm{Mo}$ differs from the one suggested in the calculations which predict a $\gamma$-soft rotor. There was no experimental indication of the oblate shape or the $\gamma$-soft rotor predicted in these Mo isotopes.

Quantum many-body theory has witnessed tremendous progress in various fields, ranging from atomic and solid-state physics to quantum chemistry and nuclear structure. Due to the inherent computational burden linked to the ab initio treatment of microscopic fermionic systems, it is desirable to obtain accurate results through low-order perturbation theory. In atomic nuclei, however, effects such as strong short-range repulsion between nucleons can spoil the convergence of the expansion and make the reliability of perturbation theory unclear. Mathematicians have devised an extensive machinery to overcome the problem of divergent expansions by making use of so-called resummation methods. In large-scale many-body applications, such schemes are often of limited use since no a priori analytical knowledge of the expansion is available. We present here eigenvector continuation as an alternative resummation tool that is both efficient and reliable because it is based on robust and simple mathematical principles.

We report benchmark calculations of the energy per particle of pure neutron matter as a function of the baryon density using three independent many-body methods: Brueckner–Bethe–Goldstone, Fermi hypernetted chain/single-operator chain, and auxiliary-field diffusion Monte Carlo. Significant technical improvements are implemented in the latter two methods. The calculations are made for two distinct families of realistic coordinate-space nucleon-nucleon potentials fit to scattering data, including the standard Argonne $v_{18}$ interaction and two of its simplified versions, and four of the new Norfolk $\mathrm{\Delta }$-full chiral effective field theory potentials. Primarily because of the advancements in the auxiliary-field diffusion Monte Carlo, we observe good agreement among the three many-body techniques up to nuclear saturation density—the maximum difference in the energy per particle is within $1.5\mathrm{MeV}$ for all the potentials we consider. At higher densities, the divergences become more important, and are mainly driven by the Fermi hypernetted chain/single-operator calculations. We also study the connection between nucleon-nucleon scattering data and the energy per particle of pure neutron matter. Our results suggest that fitting to higher-energy nucleon-nucleon scattering helps reduce the spread of energies among the models.

The Ultracold Neutron Asymmetry (UCNA) experiment was designed to measure the $\beta$-decay asymmetry parameter, $A_0$, for free neutron decay. In the experiment, polarized ultracold neutrons are transported into a decay trap, and their $\beta$-decay electrons are detected with $\approx 4\pi$ acceptance into two detector packages which provide position and energy reconstruction. The experiment also has sensitivity to $b_n$, the Fierz interference term in the neutron $\beta$-decay rate. In this work, we determine $b_n$ from the energy dependence of $A_0$ using the data taken during the UCNA 2011–2013 run. In addition, we present the same type of analysis using the earlier 2010 $A$ dataset. Motivated by improved statistics and comparable systematic errors compared to the 2010 data-taking run, we present a new $b_n$ measurement using the weighted average of our asymmetry dataset fits, to obtain $b_n=0.066\pm 0.{041}_{\text{stat}}\pm 0.{024}_{\text{syst}}$ which corresponds to a limit of $-0.012<b_n<0.144$ at the 90% confidence level.

We present a microscopic calculation of $\alpha$-cluster formation in heavy nuclei ${}^{104}\mathrm{Te}$ $(\alpha +{}^{100}\mathrm{Sn})$, ${}^{212}\mathrm{Po}$ $(\alpha +{}^{208}\mathrm{Pb})$, and their neighbors ${}^{102}\mathrm{Sn},{}^{102}\mathrm{Te},{}^{210}\mathrm{Pb}$, and ${}^{210}\mathrm{Po}$ by using the quartetting wave function approach. To improve the local density approximation, the shell structure of the core nucleus is considered, and the center-of-mass (c.m.) effective potential for the quartet is obtained self-consistently from the shell model wave functions. The $\alpha$-cluster formation and decay probabilities are obtained by solving the bound-state of the c.m. motion of the quartet and the scattering state of the formed $\alpha$ cluster in the Gurvitz approach. Striking shell effects on the $\alpha$-cluster formation probabilities are analyzed for magic numbers 50, 82, and 126. The computed $\alpha$-decay half-lives of these special nuclei are compared with the newest experimental data.

The deuteron form factors are calculated using two model wave functions obtained from the 2007 covariant spectator theory high-precision fits to $np$ scattering data. Included in the calculation is a new class of isoscalar $np$ interaction currents which are automatically generated by the nuclear force model used in these fits. If the nuclear model WJC2 is used, a precision fit (${\chi }^2$/datum $\eqsim 1$) to the Sick global analysis (GA) of all $ed$ elastic scattering data can be obtained by adjusting the unknown off-shell nucleon form factors $F_3\left(Q^2\right)$ (discussed before) and $F_4\left(Q^2\right)$ (introduced in this paper) and predicting the high-$Q^2$ behavior of the neutron charge form factor $G_{En}\left(Q^2\right)$ well beyond the region where it has been measured directly. Relativistic corrections, isoscalar interaction currents, and off-shell effects are defined and discussed, and their sizes are displayed. A rationale for extending $ed$ elastic scattering measurements to higher $Q^2$ is presented.

Decay spectroscopy of ${}^{250}\mathrm{No}$ has been performed using digital electronics and pulse-shape analysis of the fast nuclear decays for the first time. Previous studies of ${}^{250}\mathrm{No}$ reported two distinct fission decay lifetimes, related to the direct fission of the ground state and to the decay of an isomeric state but without the possibility to determine if the isomeric state decayed directly via fission or via internal electromagnetic transitions to the ground state. The data obtained in the current experiment allowed the puzzle to finally be resolved, attributing the shorter half-life of $t_{1/2}=3.8\pm 0.3\mu \mathrm{s}$ to the ground state and the longer half-life $t_{1/2}=34.9_{-3.2}^{+3.9}\mu \mathrm{s}$ to the decay of an isomeric state. ${}^{250}\mathrm{No}$ becomes, thus, one of a very few examples of very heavy nuclei with an isomeric state living considerably longer than its ground state. This phenomenon has important consequences for the nuclear-structure models aiming to determine the borders of the island of stability of superheavy elements.

Excited states of the neutron-rich nucleus ${}^{148}\mathrm{Ce}$ have been populated by neutron-induced fission of a ${}^{235}\mathrm{U}$ target. Its electromagnetic decays were studied by means of $\gamma$-ray coincidence spectroscopy with fast-timing capabilities. Lifetimes of the $2_1^{+}$ and $4_1^{+}$ states of ${}^{148}\mathrm{Ce}$ were obtained and their $E2$ decay rates deduced. The $B_{4/2}=B(E2;4_1^{+}\to 2_1^{+})/B(E2;2_1^{+}\to 0_1^{+})$ ratio indicates that ${}^{148}\mathrm{Ce}$ is a transitional nucleus while the $N=88/90$ shape phase transition evolves into a gradual change of nuclear deformation for proton numbers $Z<60$.