The Canadian Penning Trap mass spectrometer at the Californium Rare Isotope Breeder Upgrade (CARIBU) facility was used to measure the masses of eight neutron-rich isotopes of Nd and Sm. These measurements are the first to push into the region of nuclear masses relevant to the formation of the rare-earth abundance peak at $A\sim 165$ by the rapid neutron-capture process. We compare our results with theoretical predictions obtained from “reverse engineering” the mass surface that best reproduces the observed solar abundances in this region through a Markov chain Monte Carlo technique. Our measured masses are consistent with the reverse-engineering predictions for a neutron star merger wind scenario.

We demonstrate that the diffusion currents do not depend only on gradients of their corresponding charge density, but that the different diffusion charge currents are coupled. This happens in such a way that it is possible for density gradients of a given charge to generate dissipative currents of another charge. Within this scheme, the charge diffusion coefficient is best viewed as a matrix, in which the diagonal terms correspond to the usual charge diffusion coefficients, while the off-diagonal terms describe the coupling between the different currents. In this Letter, we calculate for the first time the complete diffusion matrix for hot and dense nuclear matter, including baryon, electric, and strangeness charges. We find that the baryon diffusion current is strongly affected by baryon charge gradients but also by its coupling to gradients in strangeness. The electric charge diffusion current is found to be strongly affected by electric and strangeness gradients, whereas strangeness currents depend mostly on strange and baryon gradients.

The tiny droplets of quark gluon plasma (QGP) created in high-energy nuclear collisions experience fast expansion and cooling with a lifetime of a few $\mathrm{fm}/c$. Despite the information provided by probes such as jet quenching and quarkonium suppression, and the excellent description by hydrodynamical models, direct access to the time evolution of the system remains elusive. We point out that the study of hadronically decaying $W$ bosons, notably in events with a top-antitop quark pair, can provide key novel insight into the time structure of the QGP. This is because of a unique feature, namely a time delay between the moment of the collision and that when the $W$-boson decay products start interacting with the medium. Furthermore, the length of the time delay can be constrained by selecting specific reconstructed top-quark momenta. We carry out a Monte Carlo feasibility study and find that the LHC has the potential to bring first limited information on the time structure of the QGP. Substantially increased LHC heavy-ion luminosities or future higher-energy colliders would open opportunities for more extensive studies.

The neutron-rich isotopes ${}^{58–63}\mathrm{Cr}$ were produced for the first time at the ISOLDE facility and their masses were measured with the ISOLTRAP spectrometer. The new values are up to 300 times more precise than those in the literature and indicate significantly different nuclear structure from the new mass-surface trend. A gradual onset of deformation is found in this proton and neutron midshell region, which is a gateway to the second island of inversion around $N=40$. In addition to comparisons with density-functional theory and large-scale shell-model calculations, we present predictions from the valence-space formulation of the ab initio in-medium similarity renormalization group, the first such results for open-shell chromium isotopes.

Materials containing a high proportion of grain boundaries offer significant potential for the development of radiation-resistant structural materials. However, a proper understanding of the connection between the radiation-induced microstructural behavior of a grain boundary and its impact at long natural time scales is still missing. In this Letter, point defect absorption at interfaces is summarized by a jump Robin-type condition at a coarse-grained level, wherein the role of interface microstructure is effectively taken into account. Then a concise formula linking the sink strength of a polycrystalline aggregate with its grain size is introduced and is well compared with experimental observation. Based on the derived model, a coarse-grained formulation incorporating the coupled evolution of grain boundaries and point defects is proposed, so as to underpin the study of long-time morphological evolution of grains induced by irradiation. Our simulation results suggest that the presence of point defect sources within a grain further accelerates its shrinking process, and radiation tends to trigger the extension of twin boundary sections.

Ground-state two-proton ($2p$) radioactivity is a rare decay mode found in a few very proton-rich isotopes. The $2p$ decay lifetime and properties of emitted protons carry invaluable information on nuclear structure in the presence of a low-lying proton continuum. The recently measured $2p$ decay of ${}^{67}\mathrm{Kr}$ turned out to be unexpectedly fast. Since ${}^{67}\mathrm{Kr}$ is expected to be a deformed system, we investigate the impact of deformation effects on the $2p$ radioactivity. We apply the recently developed Gamow coupled-channel framework, which allows for a precise description of three-body systems in the presence of rotational and vibrational couplings. This is the first application of a three-body approach to a two-nucleon decay from a deformed nucleus. We show that deformation couplings significantly increase the $2p$ decay width of ${}^{67}\mathrm{Kr}$; this finding explains the puzzling experimental data. The calculated angular proton-proton correlations reflect a competition between $1p$ and $2p$ decay modes in this nucleus.

A sequence of low-energy levels in ${{}_{32}{}^{78}\mathrm{Ge}}_{46}$ has been identified with spins and parity of $2^{+}$, $3^{+}$, $4^{+}$, $5^{+}$, and $6^{+}$. Decays within this band proceed strictly through $\mathrm{\Delta }J=1$ transitions, unlike similar sequences in neighboring Ge and Se nuclei. Above the $2^{+}$ level, members of this sequence do not decay into the ground-state band. Moreover, the energy staggering of this sequence has the phase that would be expected for a $\gamma$-rigid structure. The energies and branching ratios of many of the levels are described well by shell-model calculations. However, the calculated reduced transition probabilities for the $\mathrm{\Delta }J=2$ in-band transitions imply that they should have been observed, in contradiction with the experiment. Within the calculations of Davydov, Filippov, and Rostovsky for rigid-triaxial rotors with $\gamma =30°$, there are sequences of higher-spin levels connected by strong $\mathrm{\Delta }J=1$ transitions which decay in the same manner as those observed experimentally, yet are calculated at too high an excitation energy.

We analyze and propose a solution to the apparent inconsistency between our current knowledge of the equation of state of asymmetric nuclear matter, the energy of the isobaric analog state (IAS) in a heavy nucleus such as ${}^{208}\mathrm{Pb}$, and the isospin symmetry breaking forces in the nuclear medium. This is achieved by performing state-of-the-art Hartree-Fock plus random phase approximation calculations of the IAS that include all isospin symmetry breaking contributions. To this aim, we propose a new effective interaction that is successful in reproducing the IAS excitation energy without compromising other properties of finite nuclei.

The prompt $D^0$ meson azimuthal anisotropy coefficients, $v_2$ and $v_3$, are measured at midrapidity ($|y|<1.0$) in Pb-Pb collisions at a center-of-mass energy $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ per nucleon pair with data collected by the CMS experiment. The measurement is performed in the transverse momentum ($p_T$) range of 1 to $40\mathrm{GeV}/c$, for central and midcentral collisions. The $v_2$ coefficient is found to be positive throughout the $p_T$ range studied. The first measurement of the prompt $D^0$ meson $v_3$ coefficient is performed, and values up to 0.07 are observed for $p_T$ around $4\mathrm{GeV}/c$. Compared to measurements of charged particles, a similar $p_T$ dependence, but smaller magnitude for $p_T<6\mathrm{GeV}/c$, is found for prompt $D^0$ meson $v_2$ and $v_3$ coefficients. The results are consistent with the presence of collective motion of charm quarks at low $p_T$ and a path length dependence of charm quark energy loss at high $p_T$, thereby providing new constraints on the theoretical description of the interactions between charm quarks and the quark-gluon plasma.

Thermalized matter created in noncentral relativistic heavy-ion collisions is expected to be tilted in the reaction plane with respect to the beam axis. The most notable consequence of this forward-backward symmetry breaking is the observation of rapidity-odd directed flow for charged particles. On the other hand, the production points for heavy quarks are forward-backward symmetric and shifted in the transverse plane with respect to the fireball. The drag on heavy quarks from the asymmetrically distributed thermalized matter generates substantial directed flow for heavy flavor mesons. We predict a very large rapidity-odd directed flow of $D$ mesons in noncentral Au-Au collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$, several times larger than for charged particles. A possible experimental observation of a large directed flow for heavy flavor mesons would represent an almost direct probe of the three-dimensional distribution of matter in heavy-ion collisions.

The low-energy dipole excitations in ${}^{24}\mathrm{Mg}$ are investigated within the Skyrme quasiparticle random phase approximation for axial nuclei. The calculations with the force SLy6 reveal a remarkable feature: the lowest $I^{\pi }K=1^{-}1$ excitation ($E=7.92\mathrm{MeV}$) in ${}^{24}\mathrm{Mg}$ is a vortical toroidal state (TS) representing a specific vortex-antivortex realization of the well-known spherical Hill’s vortex in a strongly deformed axial confinement. This is a striking example of an individual TS which can be much more easily discriminated in experiment than the toroidal dipole resonance embracing many states. The TS acquires the lowest energy due to the huge prolate axial deformation in ${}^{24}\mathrm{Mg}$. The result persists for different Skyrme parametrizations (SLy6, SVbas, SkM*). We analyze spectroscopic properties of the TS and its relation with the cluster structure of ${}^{24}\mathrm{Mg}$. Similar TSs could exist in other highly prolate light nuclei. They could serve as promising tests for various reactions to probe a vortical (toroidal) nuclear flow.

The structure of deformed neutron-rich nuclei in the rare-earth region is of significant interest for both the astrophysics and nuclear structure fields. At present, a complete explanation for the observed peak in the elemental abundances at $A\sim 160$ eludes astrophysicists, and models depend on accurate quantities, such as masses, lifetimes, and branching ratios of deformed neutron-rich nuclei in this region. Unusual nuclear structure effects are also observed, such as the unexpectedly low energies of the first $2^{+}$ levels in some even-even nuclei at $N=98$. In order to address these issues, mass and $\beta$-decay spectroscopy measurements of the ${}^{160}{\mathrm{Eu}}_{97}$ and ${}^{162}{\mathrm{Eu}}_{99}$ nuclei were performed at the Californium Rare Isotope Breeder Upgrade radioactive beam facility at Argonne National Laboratory. Evidence for a gap in the single-particle neutron energies at $N=98$ and for large deformation (${\beta }_2\sim 0.3$) is discussed in relation to the unusual phenomena observed at this neutron number.

The (${}^{12}\mathrm{N}$, ${}^{12}\mathrm{C}$) charge-exchange reaction at $175\mathrm{MeV}/u$ was developed as a novel probe for studying the isovector spin giant monopole resonance (IVSMR), whose properties are important for better understanding the bulk properties of nuclei and asymmetric nuclear matter. This probe, now available through the production of ${}^{12}\mathrm{N}$ as a secondary rare-isotope beam, is exothermic, is strongly absorbed at the surface of the target nucleus, and provides selectivity for spin-transfer excitations. All three properties enhance the excitation of the IVSMR compared to other, primarily light-ion, probes, which have been used to study the IVSMR thus far. The ${}^{90}\mathrm{Zr}({}^{12}\mathrm{N},{}^{12}\mathrm{C})$ reaction was measured and the excitation energy spectra up to about 70 MeV for both the spin-transfer and non-spin-transfer channels were deduced separately by tagging the decay by $\gamma$ emission from the ${}^{12}\mathrm{C}$ ejectile. Besides the well-known Gamow-Teller and isobaric analog transitions, a clear signature of the IVSMR was identified. By comparing with the results from light-ion reactions on the same target nucleus and theoretical predictions, the suitability of this new probe for studying the IVSMR was confirmed.

We compute the electric conductivity of quark matter at finite temperature $T$ and a quark chemical potential $\mu$ under a magnetic field $B$ beyond the lowest Landau level approximation. The electric conductivity transverse to $B$ is dominated by the Hall conductivity ${\sigma }_H$. For the longitudinal conductivity ${\sigma }_{\parallel }$, we need to solve kinetic equations. Then, we numerically find that ${\sigma }_{\parallel }$ has only a mild dependence on $\mu$ and the quark mass $m_q$. Moreover, ${\sigma }_{\parallel }$ first decreases and then linearly increases as a function of $B$, leading to an intermediate $B$ region that looks consistent with the experimental signature for the chiral magnetic effect. We also point out that ${\sigma }_{\parallel }$ at a nonzero $B$ remains within the range of the lattice-QCD estimate at $B=0$.

We observed the atomic $1s$ and $2p$ states of ${\pi }^{-}$ bound to ${}^{121}\mathrm{Sn}$ nuclei as distinct peak structures in the missing mass spectra of the ${}^{122}\text{Sn}(d,{}^3\text{He})$ nuclear reaction. A very intense deuteron beam and a spectrometer with a large angular acceptance let us achieve a potential of discovery, which includes the capability of determining the angle-dependent cross sections with high statistics. The $2p$ state in a Sn nucleus was observed for the first time. The binding energies and widths of the pionic states are determined and found to be consistent with previous experimental results of other Sn isotopes. The spectrum is measured at finite reaction angles for the first time. The formation cross sections at the reaction angles between 0° and 2° are determined. The observed reaction-angle dependence of each state is reproduced by theoretical calculations. However, the quantitative comparison with our high-precision data reveals a significant discrepancy between the measured and calculated formation cross sections of the pionic $1s$ state.