A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the $r$ process. As a proof of principle, the $\gamma$ spectra from the $\beta$ decay of ${}^{76}\mathrm{Ga}$ have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and $\gamma$-ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the ${}^{75}\mathrm{Ge}(n,\gamma ){}^{76}\mathrm{Ge}$ cross section and reaction rate.

We employ a small $x$ color glass condensate (CGC)+ nonrelativistic QCD (NRQCD) formalism to compute $J/\psi$ production at low $p_{\perp }$ in proton-proton collisions at collider energies. Very good agreement is obtained for total cross sections, rapidity distributions, and low momentum $p_{\perp }$ distributions. Similar agreement is obtained for ${\psi }^{\prime }$ production. We observe an overlap region in $p_{\perp }$ where our results match smoothly to those obtained in a next-to-leading order collinearly factorized NRQCD formalism. The relative contribution of color singlet and color octet contributions can be quantified in the $\mathrm{CGC}+\mathrm{NRQCD}$ framework, with the former contributing approximately 10% of the total cross section.

We present the first Green’s function Monte Carlo calculations of light nuclei with nuclear interactions derived from chiral effective field theory up to next-to-next-to-leading order. Up to this order, the interactions can be constructed in a local form and are therefore amenable to quantum Monte Carlo calculations. We demonstrate a systematic improvement with each order for the binding energies of $A=3$ and $A=4$ systems. We also carry out the first few-body tests to study perturbative expansions of chiral potentials at different orders, finding that higher-order corrections are more perturbative for softer interactions. Our results confirm the necessity of a three-body force for correct reproduction of experimental binding energies and radii, and pave the way for studying few- and many-nucleon systems using quantum Monte Carlo methods with chiral interactions.

We present the first ab initio calculations for $p$-shell single-$\mathrm{\Lambda }$ hypernuclei. For the solution of the many-baryon problem, we develop two variants of the no-core shell model with explicit $\mathrm{\Lambda }$ and ${\mathrm{\Sigma }}^{+},{\mathrm{\Sigma }}^0,{\mathrm{\Sigma }}^{-}$ hyperons including $\mathrm{\Lambda }\text{−}\mathrm{\Sigma }$ conversion, optionally supplemented by a similarity renormalization group transformation to accelerate model-space convergence. In addition to state-of-the-art chiral two- and three-nucleon interactions, we use leading-order chiral hyperon-nucleon interactions and a recent meson-exchange hyperon-nucleon interaction. We validate the approach for $s$-shell hypernuclei and apply it to $p$-shell hypernuclei, in particular to ${}_{\mathrm{\Lambda }}{}^7\mathrm{Li}$, ${}_{\mathrm{\Lambda }}{}^9\mathrm{Be}$, and ${}_{\mathrm{\Lambda }}{}^{13}\mathrm{C}$. We show that the chiral hyperon-nucleon interactions provide ground-state and excitation energies that generally agree with experiment within the cutoff dependence. At the same time we demonstrate that hypernuclear spectroscopy provides tight constraints on the hyperon-nucleon interactions.

We present variational Monte Carlo calculations of the neutron matter equation of state using chiral nuclear forces. The ground-state wave function of neutron matter, containing nonperturbative many-body correlations, is obtained from auxiliary-field quantum Monte Carlo simulations of up to about 340 neutrons interacting on a $10^3$ discretized lattice. The evolution Hamiltonian is chosen to be attractive and spin independent in order to avoid the fermion sign problem and is constructed to best reproduce broad features of the chiral nuclear force. This is facilitated by choosing a lattice spacing of 1.5 fm, corresponding to a momentum-space cutoff of $\mathrm{\Lambda }=414\mathrm{MeV}/c$, a resolution scale at which strongly repulsive features of nuclear two-body forces are suppressed. Differences between the evolution potential and the full chiral nuclear interaction (Entem and Machleidt $\mathrm{\Lambda }=414\mathrm{MeV}$ [L. Coraggio et al., Phys. Rev. C 87, 014322 (2013)]) are then treated perturbatively. Our results for the equation of state are compared to previous quantum Monte Carlo simulations that employed chiral two-body forces at next-to-next-to-leading order (N2LO). In addition, we include the effects of three-body forces at N2LO, which provide important repulsion at densities higher than $0.02{\mathrm{fm}}^{-3}$ as well as two-body forces at next-to-next-to-next-to-leading order.

We follow the time evolution of non-Abelian gauge bosons from far-from-equilibrium initial conditions to thermal equilibrium by numerically solving an effective kinetic equation that becomes accurate in the weak coupling limit. We consider isotropic initial conditions that are either highly overoccupied or underoccupied. We find that overoccupied systems thermalize through a self-similar cascade reaching equilibrium in multiples of a thermalization time $t_{\text{eq}}\approx 72./(1+0.12\log {\lambda }^{-1})\times 1/{\lambda }^{2}T$, whereas underoccupied systems undergo a “bottom-up” thermalization in a time $t_{\text{eq}}\approx [34.+21.\log (Q/T)]/(1+0.037\log {\lambda }^{-1})\times {(Q/T)}^{1/2}/{\lambda }^{2}T$, where $Q$ is the characteristic momentum scale of the initial condition. We apply this result to model initial stages of heavy-ion collisions and find rapid thermalization roughly in a time $Q{t}_{\text{eq}}\lesssim 10$ or $t_{\text{eq}}\lesssim 1\mathrm{fm}/c$.

The reduced transition probability $B(E2;0^{+}\to 2^{+})$ has been measured for the neutron-rich nucleus ${}^{74}\mathrm{Ni}$ in an intermediate energy Coulomb excitation experiment performed at the National Superconducting Cyclotron Laboratory at Michigan State University. The obtained $B(E2;0^{+}\to 2^{+})=642_{-226}^{+216}{e}^2{\mathrm{fm}}^4$ value defines a trend which is unexpectedly small if referred to ${}^{70}\mathrm{Ni}$ and to a previous indirect determination of the transition strength in ${}^{74}\mathrm{Ni}$. This indicates a reduced polarization of the $Z=28$ core by the valence neutrons. Calculations in the $pfgd$ model space reproduce well the experimental result indicating that the $B(E2)$ strength predominantly corresponds to neutron excitations. The ratio of the neutron and proton multipole matrix elements supports such an interpretation.

The quasifission mechanism hinders fusion in heavy systems through breakup within zeptoseconds into two fragments with partial mass equilibration. Its dependence on the structure of both the collision partners and the final fragments is a key question. Our original approach is to combine an experimental measurement of the fragments’ mass-angle correlations in ${}^{40}\mathrm{Ca}+{}^{238}\mathrm{U}$ with microscopic quantum calculations. We demonstrate an unexpected interplay between the orientation of the prolate deformed ${}^{238}\mathrm{U}$ with quantum shell effects in the fragments. In particular, calculations show that only collisions with the tip of ${}^{238}\mathrm{U}$ produce quasifission fragments in the magic $Z=82$ region, while collisions with the side are the only ones that may result in fusion.

We investigate the properties of charmonia in strong magnetic fields by using QCD sum rules. We show how to implement the mixing effects between ${\eta }_c$ and $J/\psi$ on the basis of field-theoretical approaches, and then show that the sum rules are saturated by the mixing effects with phenomenologically determined parameters. Consequently, we find that the mixing effects are the dominant contribution to the mass shifts of the static charmonia in strong magnetic fields.

Beyond mean-field methods are very successful tools for the description of large-amplitude collective motion for even-even atomic nuclei. The state-of-the-art framework of these methods consists in a generator coordinate method based on angular-momentum and particle-number projected triaxially deformed Hartree-Fock-Bogoliubov (HFB) states. The extension of this scheme to odd-mass nuclei is a long-standing challenge. We present for the first time such an extension, where the generator coordinate space is built from self-consistently blocked one-quasiparticle HFB states. One of the key points for this success is that the same Skyrme interaction is used for the mean-field and the pairing channels, thus avoiding problems related to the violation of the Pauli principle. An application to ${}^{25}\mathrm{Mg}$ illustrates the power of our method, as agreement with experiment is obtained for the spectrum, electromagnetic moments, and transition strengths, for both positive and negative parity states and without the necessity for effective charges or effective moments. Although the effective interaction still requires improvement, our study opens the way to systematically describe odd-$A$ nuclei throughout the nuclear chart.

We present the first ab initio construction of valence-space Hamiltonians for medium-mass nuclei based on chiral two- and three-nucleon interactions using the in-medium similarity renormalization group. When applied to the oxygen isotopes, we find experimental ground-state energies are well reproduced, including the flat trend beyond the drip line at ${}^{24}\mathrm{O}$. Similarly, natural-parity spectra in ${}^{21,22,23,24}\mathrm{O}$ are in agreement with experiment, and we present predictions for excited states in ${}^{25,26}\mathrm{O}$. The results exhibit a weak dependence on the harmonic-oscillator basis parameter and reproduce spectroscopy within the standard $sd$ valence space.

We derive and compute effective valence-space shell-model interactions from ab initio coupled-cluster theory and apply them to open-shell and neutron-rich oxygen and carbon isotopes. Our shell-model interactions are based on nucleon-nucleon and three-nucleon forces from chiral effective-field theory. We compute the energies of ground and low-lying states, and find good agreement with experiment. In particular, our computed $2^{+}$ states are consistent with $N=14,16$ shell closures in ${}^{22,24}\mathrm{O}$, and a weaker $N=14$ shell closure in ${}^{20}\mathrm{C}$. We find good agreement between our coupled-cluster effective-interaction results with those obtained from standard single-reference coupled-cluster calculations for up to eight valence neutrons.

We report the first measurement of charmed-hadron ($D^0$) production via the hadronic decay channel ($D^0\to K^{-}+{\pi }^{+}$) in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ with the STAR experiment. The charm production cross section per nucleon-nucleon collision at midrapidity scales with the number of binary collisions, $N_{\mathrm{bin}}$, from $p+p$ to central $\mathrm{Au}+\mathrm{Au}$ collisions. The $D^0$ meson yields in central $\mathrm{Au}+\mathrm{Au}$ collisions are strongly suppressed compared to those in $p+p$ scaled by $N_{\mathrm{bin}}$, for transverse momenta $p_T>3\mathrm{GeV}/c$, demonstrating significant energy loss of charm quarks in the hot and dense medium. An enhancement at intermediate $p_{\mathrm{T}}$ is also observed. Model calculations including strong charm-medium interactions and coalescence hadronization describe our measurements.

Delayed $\gamma$-ray cascades, originating from the decay of $(6^{+})$ isomeric states, in the very neutron-rich, semimagic isotopes ${}^{136,138}$Sn have been observed following the projectile fission of a ${}^{238}$U beam at RIBF, RIKEN. The wave functions of these isomeric states are proposed to be predominantly a fully aligned pair of $f_{7/2}$ neutrons. Shell-model calculations, performed using a realistic effective interaction, reproduce well the energies of the excited states of these nuclei and the measured transition rates, with the exception of the $B(E2;6^{+}\to 4^{+})$ rate of ${}^{136}$Sn, which deviates from a simple seniority scheme. Empirically reducing the $\nu f_{7/2}^2$ orbit matrix elements produces a $4_1^{+}$ state with almost equal seniority 2 and 4 components, correctly reproducing the experimental $B(E2;6^{+}\to 4^{+})$ rate of ${}^{136}$Sn. These data provide a key benchmark for shell-model interactions far from stability.

The first determination of radii of point proton distribution (proton radii) of ${}^{12–17}\mathrm{B}$ from charge-changing cross sections (${\sigma }_{\mathrm{CC}}$) measurements at the FRS, GSI, Darmstadt is reported. The proton radii are deduced from a finite-range Glauber model analysis of the ${\sigma }_{\mathrm{CC}}$. The radii show an increase from ${}^{13}\mathrm{B}$ to ${}^{17}\mathrm{B}$ and are consistent with predictions from the antisymmetrized molecular dynamics model for the neutron-rich nuclei. The measurements show the existence of a thick neutron surface with neutron-proton radius difference of 0.51(0.11) fm in ${}^{17}\mathrm{B}$.

Recent results in $d+\mathrm{Au}$ and $p+\mathrm{Pb}$ collisions at RHIC and the LHC provide evidence for collective expansion and flow of the created medium. We propose a control set of experiments to directly compare particle emission patterns from $p+\mathrm{Pb}$, $d+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$ or $t+\mathrm{Au}$ collisions at the same $\sqrt{s_{NN}}$ . Using a Monte Carlo Glauber simulation we find that a ${}^3\mathrm{He}$ or triton projectile, with a realistic wave function description, induces a significant intrinsic triangular shape to the initial medium. If the system lives long enough, this survives into a significant third-order flow moment $v_3$ even with viscous damping. By comparing systems with one, two, and three initial hot spots, one could disentangle the effects from the initial spatial distribution of the deposited energy and viscous damping. These are key tools for answering the question of how small a droplet of matter is necessary to form a quark-gluon plasma described by nearly inviscid hydrodynamics.

Symmetries in nature offer very simple descriptions of complex systems. Partial Dynamical Symmetries (PDS) can considerably broaden their relevance. To present the first extensive test of a PDS for nuclei, we compare an SU(3) PDS to gamma to ground band $B(E2)$ values for 47 deformed nuclei. The parameter-free PDS is found to be quite successful, but with characteristic discrepancies, suggesting that symmetry remnants are more pervasive than heretofore realized. Furthermore, the SU(3) PDS gives new insights into collective models (e.g., interacting boson approximation). If these reproduce the PDS, they reflect finite size effects, while differences from the PDS point to SU(3) configuration mixing.