In the standard picture of the crust of a neutron star, matter there is simple: a body-centered-cubic lattice of nuclei immersed in an essentially uniform electron gas. We show that, at densities above that for neutron drip ($\sim 4\times {10}^{11}\mathrm{g}{\mathrm{cm}}^{-3}$ or roughly one-thousandth of nuclear matter density), the interstitial neutrons give rise to an attractive interaction between nuclei that renders the lattice unstable. We argue that the likely equilibrium structure is similar to that in displacive ferroelectric materials such as ${\mathrm{BaTiO}}_3$. As a consequence, the properties of matter in the inner crust are expected to be much richer than previously appreciated, and we mention possible consequences for observable neutron star properties.

We argue that relativistic nuclear collisions may provide experimental evidence of $\alpha$ clustering in light nuclei. A light $\alpha$-clustered nucleus has a large intrinsic deformation. When collided against a heavy nucleus at very high energies, this deformation transforms into the deformation of the fireball in the transverse plane. The subsequent collective evolution of the fireball leads to harmonic flow reflecting the deformation of the initial shape, which can be measured with standard methods of relativistic heavy-ion collisions. We illustrate the feasibility of the idea by modeling the ${}^{12}\mathrm{C}\text{−}{}^{208}\mathrm{Pb}$ collisions and point out that very significant quantitative and qualitative differences between the $\alpha$-clustered and uniform ${}^{12}\mathrm{C}$ nucleus occur in such quantities as the triangular flow, its event-by-event fluctuations, or the correlations of the elliptic and triangular flows. The proposal offers a possibility of studying low-energy nuclear structure phenomena with “snapshots” made with relativistic heavy-ion collisions.

The new regime of resonant nuclear photoexcitation rendered possible by x-ray free-electron laser beams interacting with solid state targets is investigated theoretically. Our results unexpectedly show that secondary processes coupling nuclei to the atomic shell in the created cold high-density plasma can dominate direct photoexcitation. As an example, we discuss the case of ${}^{93m}\mathrm{Mo}$ isomer depletion for which nuclear excitation by electron capture as a secondary process is shown to be orders of magnitude more efficient than the direct laser-nucleus interaction. General arguments revisiting the role of the x-ray free-electron laser in nuclear experiments involving solid-state targets are further deduced.

We determine the magnetization of quantum chromodynamics for several temperatures around and above the transition between the hadronic and the quark-gluon phases of strongly interacting matter. We obtain a paramagnetic response that increases in strength with the temperature. We argue that due to this paramagnetism, chunks of quark-gluon plasma produced in noncentral heavy ion collisions should become squeezed perpendicular to the magnetic field. This anisotropy will then contribute to the elliptic flow $v_2$ observed in such collisions, in addition to the pressure gradient that is usually taken into account. We present a simple estimate for the magnitude of this new effect and a rough comparison to the effect due to the initial collision geometry. We conclude that the paramagnetic effect might have a significant impact on the value of $v_2$.

Neutron star (NS) merger ejecta offer a viable site for the production of heavy $r$-process elements with nuclear mass numbers $A\gtrsim 140$. The crucial role of fission recycling is responsible for the robustness of this site against many astrophysical uncertainties, but calculations sensitively depend on nuclear physics. In particular, the fission fragment yields determine the creation of $110\lesssim A\lesssim 170$ nuclei. Here, we apply a new scission-point model, called SPY, to derive the fission fragment distribution (FFD) of all relevant neutron-rich, fissioning nuclei. The model predicts a doubly asymmetric FFD in the abundant $A\simeq 278$ mass region that is responsible for the final recycling of the fissioning material. Using ejecta conditions based on relativistic NS merger calculations, we show that this specific FFD leads to a production of the $A\simeq 165$ rare-earth peak that is nicely compatible with the abundance patterns in the Sun and metal-poor stars. This new finding further strengthens the case of NS mergers as possible dominant origin of $r$ nuclei with $A\gtrsim 140$.

We use the classical Bogomol’nyi-Prasad-Sommerfield (BPS) soliton solutions of the BPS Skyrme model together with corrections from the collective coordinate quantization of spin and isospin, the electrostatic Coulomb energies, and a small explicit breaking of the isospin symmetry—accounting for the proton-neutron mass difference—to calculate nuclear binding energies. We find that the resulting binding energies are already in excellent agreement with their physical values for heavier nuclei, demonstrating thereby that the BPS Skyrme model is a distinguished starting point for a detailed quantitative investigation of nuclear and low-energy strong interaction physics.

The most precise determination of the neutron lifetime using the beam method was completed in 2005 and reported a result of ${\tau }_n=(886.3\pm 1.2[\mathrm{stat}]\pm 3.2[\mathrm{syst}])\mathrm{s}$. The dominant uncertainties were attributed to the absolute determination of the fluence of the neutron beam (2.7 s). The fluence was measured with a neutron monitor that counted the neutron-induced charged particles from absorption in a thin, well-characterized ${}^6\mathrm{Li}$ deposit. The detection efficiency of the monitor was calculated from the areal density of the deposit, the detector solid angle, and the evaluated nuclear data file, ENDF/B-VI ${}^6\mathrm{Li}(n,t){}^4\mathrm{He}$ thermal neutron cross section. In the current work, we measure the detection efficiency of the same monitor used in the neutron lifetime measurement with a second, totally absorbing neutron detector. This direct approach does not rely on the ${}^6\mathrm{Li}(n,t){}^4\mathrm{He}$ cross section or any other nuclear data. The detection efficiency is consistent with the value used in 2005 but is measured with a precision of 0.057%, which represents a fivefold improvement in the uncertainty. We verify the temporal stability of the neutron monitor through ancillary measurements, allowing us to apply the measured neutron monitor efficiency to the lifetime result from the 2005 experiment. The updated lifetime is ${\tau }_n=(887.7\pm 1.2[\mathrm{stat}]\pm 1.9[\mathrm{syst}])\mathrm{s}$.

The PHENIX collaboration at the Relativistic Heavy Ion Collider (RHIC) reports measurements of azimuthal dihadron correlations near midrapidity in $d+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. These measurements complement recent analyses by experiments at the Large Hadron Collider (LHC) involving central $p+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$, which have indicated strong anisotropic long-range correlations in angular distributions of hadron pairs. The origin of these anisotropies is currently unknown. Various competing explanations include parton saturation and hydrodynamic flow. We observe qualitatively similar, but larger, anisotropies in $d+\mathrm{Au}$ collisions at RHIC compared to those seen in $p+\mathrm{Pb}$ collisions at the LHC. The larger extracted $v_2$ values in $d+\mathrm{Au}$ are consistent with expectations from hydrodynamic calculations owing to the larger expected initial-state eccentricity compared with that from $p+\mathrm{Pb}$ collisions. When both are divided by an estimate of the initial-state eccentricity the scaled anisotropies follow a common trend with multiplicity that may extend to heavy ion data at RHIC and the LHC, where the anisotropies are widely thought to arise from hydrodynamic flow.

We present possible indications for flavor separation during the QCD crossover transition based on continuum extrapolated lattice QCD calculations of higher order susceptibilities. We base our findings on flavor-specific quantities in the light and strange quark sector. We propose a possible experimental verification of our prediction, based on the measurement of higher order moments of identified particle multiplicities. Since all our calculations are performed at zero baryochemical potential, these results are of particular relevance for the heavy-ion program at the LHC.

Neutrinoless double beta decay is a process that violates lepton number conservation. It is predicted to occur in extensions of the standard model of particle physics. This Letter reports the results from phase I of the Germanium Detector Array (GERDA) experiment at the Gran Sasso Laboratory (Italy) searching for neutrinoless double beta decay of the isotope ${}^{76}\mathrm{Ge}$. Data considered in the present analysis have been collected between November 2011 and May 2013 with a total exposure of 21.6 kg yr. A blind analysis is performed. The background index is about $1\times {10}^{-2}\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$ after pulse shape discrimination. No signal is observed and a lower limit is derived for the half-life of neutrinoless double beta decay of ${}^{76}\mathrm{Ge}$, $T_{1/2}^{0\nu }>2.1\times {10}^{25}\mathrm{yr}$ (90% C.L.). The combination with the results from the previous experiments with ${}^{76}\mathrm{Ge}$ yields $T_{1/2}^{0\nu }>3.0\times {10}^{25}\mathrm{yr}$ (90% C.L.).

A high-resolution $\alpha$, x-ray, and $\gamma$-ray coincidence spectroscopy experiment was conducted at the GSI Helmholtzzentrum für Schwerionenforschung. Thirty correlated $\alpha$-decay chains were detected following the fusion-evaporation reaction ${}^{48}\mathrm{Ca}+{}^{243}\mathrm{Am}$. The observations are consistent with previous assignments of similar decay chains to originate from element $Z=115$. For the first time, precise spectroscopy allows the derivation of excitation schemes of isotopes along the decay chains starting with elements $Z>112$. Comprehensive Monte Carlo simulations accompany the data analysis. Nuclear structure models provide a first level interpretation.

The plasma astrophysical $S$ factor for the ${}^3\mathrm{He}(d,p){}^4\mathrm{He}$ fusion reaction was measured for the first time at temperatures of few keV, using the interaction of intense ultrafast laser pulses with molecular deuterium clusters mixed with ${}^3\mathrm{He}$ atoms. Different proportions of ${\mathrm{D}}_2$ and ${}^3\mathrm{He}$ or ${\mathrm{CD}}_4$ and ${}^3\mathrm{He}$ were mixed in the gas target in order to allow the measurement of the cross section for the ${}^3\mathrm{He}(d,p){}^4\mathrm{He}$ reaction. The yield of 14.7 MeV protons from the ${}^3\mathrm{He}(d,p){}^4\mathrm{He}$ reaction was measured in order to extract the astrophysical $S$ factor at low energies. Our result is in agreement with other $S$ factor parametrizations found in the literature.

Neutron time-of-flight spectra from inertial confinement fusion experiments with tritium-filled targets have been measured at the National Ignition Facility. These spectra represent a significant improvement in energy resolution and statistics over previous measurements, and afford the first definitive observation of a peak resulting from sequential decay through the ground state of ${}^5\mathrm{He}$ at low reaction energies $E_{\mathrm{c}.\mathrm{m}.}\lesssim 100\mathrm{keV}$. To describe the spectrum, we have developed an $R$-matrix model that accounts for interferences from fermion symmetry and intermediate states, and show these effects to be non-negligible. We also find the spectrum can be described by sequential decay through $\ell =1$ states in ${}^5\mathrm{He}$, which differs from previous interpretations.

The neutron-rich isotopes of cadmium up to the $N=82$ shell closure have been investigated by high-resolution laser spectroscopy. Deep-uv excitation at 214.5 nm and radioactive-beam bunching provided the required experimental sensitivity. Long-lived isomers are observed in ${}^{127}\mathrm{Cd}$ and ${}^{129}\mathrm{Cd}$ for the first time. One essential feature of the spherical shell model is unambiguously confirmed by a linear increase of the $11/2^{-}$ quadrupole moments. Remarkably, this mechanism is found to act well beyond the $h_{11/2}$ shell.