For a massless gas with a constant cross section in a homogeneous, isotropically expanding spacetime we reformulate the relativistic Boltzmann equation as a set of nonlinear coupled moment equations. For a particular initial condition this set can be solved exactly, yielding the first analytical solution of the Boltzmann equation for an expanding system. The nonequilibrium behavior of this relativistic gas can be mapped onto that of a homogeneous, static nonrelativistic gas of Maxwell molecules.

Neutron-rich ${}^{96,98}\mathrm{Sr}$ isotopes have been investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross sections. These results allow, for the first time, the drawing of definite conclusions about the shape coexistence of highly deformed prolate and spherical configurations. In particular, a very small mixing between the coexisting states is observed, contrary to other mass regions where strong mixing is present. Experimental results have been compared to beyond-mean-field calculations using the Gogny D1S interaction in a five-dimensional collective Hamiltonian formalism, which reproduce the shape change at $N=60$.

We analyze primary $\gamma$-ray spectra of the odd-odd ${}^{238}\mathrm{Np}$ nucleus extracted from ${}^{237}\mathrm{Np}(d,p\gamma ){}^{238}\mathrm{Np}$ coincidence data measured at the Oslo Cyclotron Laboratory. The primary $\gamma$ spectra cover an excitation-energy region of $0\le E_i\le 5.4\mathrm{MeV}$, and allow us to perform a detailed study of the $\gamma$-ray strength as a function of excitation energy. Hence, we can test the validity of the generalized Brink-Axel hypothesis, which, in its strictest form, claims no excitation-energy dependence on the $\gamma$ strength. In this work, using the available high-quality ${}^{238}\mathrm{Np}$ data, we show that the $\gamma$-ray strength function is to a very large extent independent of the initial and final states. Thus, for the first time, the generalized Brink-Axel hypothesis is experimentally verified for $\gamma$ transitions between states in the quasicontinuum region, not only for specific collective resonances, but also for the full strength below the neutron separation energy. Based on our findings, the necessary criteria for the generalized Brink-Axel hypothesis to be fulfilled are outlined.

We report the determination of the $Q_{\mathrm{EC}}$ value of the mirror transition of ${}^{11}\mathrm{C}$ by measuring the atomic masses of ${}^{11}\mathrm{C}$ and ${}^{11}\mathrm{B}$ using Penning trap mass spectrometry. More than an order of magnitude improvement in precision is achieved as compared to the 2012 Atomic Mass Evaluation (Ame2012) [Chin. Phys. C 36, 1603 (2012)]. This leads to a factor of 3 improvement in the calculated $\mathcal{F}t$ value. Using the new value, $Q_{\mathrm{EC}}=1981.690(61)\mathrm{keV}$, the uncertainty on $\mathcal{F}t$ is no longer dominated by the uncertainty on the $Q_{\mathrm{EC}}$ value. Based on this measurement, we provide an updated estimate of the Gamow-Teller to Fermi mixing ratio and standard model values of the correlation coefficients.

We determine the distribution of linearly polarized gluons of a dense target at small $x$ by solving the Balitsky–Jalilian-Marian–Iancu–McLerran–Weigert–Leonidov–Kovner rapidity evolution equations. From these solutions, we estimate the amplitude of $\sim \cos 2\varphi$ azimuthal asymmetries in deep inelastic scattering dijet production at high energies. We find sizable long-range in rapidity azimuthal asymmetries with a magnitude in the range of $v_2=⟨\cos 2\varphi ⟩\sim 10\%$.

Two short-lived isotopes ${}^{221}\mathrm{U}$ and ${}^{222}\mathrm{U}$ were produced as evaporation residues in the fusion reaction ${}^{50}\mathrm{Ti}+{}^{176}\mathrm{Yb}$ at the gas-filled recoil separator TASCA. An $\alpha$ decay with an energy of $E_{\alpha }=9.31(5)\mathrm{MeV}$ and half-life $T_{1/2}=4.7(7)\mu \mathrm{s}$ was attributed to ${}^{222}\mathrm{U}$. The new isotope ${}^{221}\mathrm{U}$ was identified in $\alpha$-decay chains starting with $E_{\alpha }=9.71(5)\mathrm{MeV}$ and $T_{1/2}=0.66(14)\mu \mathrm{s}$ leading to known daughters. Synthesis and detection of these unstable heavy nuclei and their descendants were achieved thanks to a fast data readout system. The evolution of the $N=126$ shell closure and its influence on the stability of uranium isotopes are discussed within the framework of $\alpha$-decay reduced width.

We report the observation of transverse polarization-dependent azimuthal correlations in charged pion pair production with the STAR experiment in $p^{\uparrow }+p$ collisions at RHIC. These correlations directly probe quark transversity distributions. We measure signals in excess of 5 standard deviations at high transverse momenta, at high pseudorapidities $\eta >0.5$, and for pair masses around the mass of the $\rho$ meson. This is the first direct transversity measurement in $p+p$ collisions.

Masses adjacent to the classical waiting-point nuclide ${}^{130}\mathrm{Cd}$ have been measured by using the Penning-trap spectrometer ISOLTRAP at ISOLDE/CERN. We find a significant deviation of over 400 keV from earlier values evaluated by using nuclear beta-decay data. The new measurements show the reduction of the $N=82$ shell gap below the doubly magic ${}^{132}\mathrm{Sn}$. The nucleosynthesis associated with the ejected wind from type-II supernovae as well as from compact object binary mergers is studied, by using state-of-the-art hydrodynamic simulations. We find a consistent and direct impact of the newly measured masses on the calculated abundances in the $A=128–132$ region and a reduction of the uncertainties from the precision mass input data.

The isospin mixing was deduced in the compound nucleus ${}^{80}\mathrm{Zr}$ at an excitation energy of $E^{*}=54\mathrm{MeV}$ from the $\gamma$ decay of the giant dipole resonance. The reaction ${}^{40}\mathrm{Ca}+{}^{40}\mathrm{Ca}$ at $E_{\text{beam}}=136\mathrm{MeV}$ was used to form the compound nucleus in the isospin $I=0$ channel, while the reaction ${}^{37}\mathrm{Cl}+{}^{44}\mathrm{Ca}$ at $E_{\text{beam}}=95\mathrm{MeV}$ was used as the reference reaction. The $\gamma$ rays were detected with the AGATA demonstrator array coupled with ${\mathrm{LaBr}}_3$:Ce detectors. The temperature dependence of the isospin mixing was obtained and the zero-temperature value deduced. The isospin-symmetry-breaking correction ${\delta }_C$ used for the Fermi superallowed transitions was extracted and found to be consistent with $\beta$-decay data.

The well-known Levinger-Bethe photonuclear sum rule relates the strength of the photoexcitation of the giant dipole resonance in a nucleus to the number of nucleons in that nucleus. I extend this sum rule to the case of virtual photons and relate the size of the magnetic polarizability of a nucleus to the $Q^2$ slope of the transverse virtual photoabsorption cross section integrated over the energy in the nuclear range. I check this sum rule for the deuteron where necessary data is available, discuss possible applications and connection with other sum rules postulated in the literature.

Collisions between prolate uranium nuclei are used to study how particle production and azimuthal anisotropies depend on initial geometry in heavy-ion collisions. We report the two- and four-particle cumulants, $v_2\{2\}$ and $v_2\{4\}$, for charged hadrons from $\mathrm{U}+\mathrm{U}$ collisions at $\sqrt{s_{\mathrm{NN}}}=193\mathrm{GeV}$ and $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$. Nearly fully overlapping collisions are selected based on the energy deposited by spectators in zero degree calorimeters (ZDCs). Within this sample, the observed dependence of $v_2\{2\}$ on multiplicity demonstrates that ZDC information combined with multiplicity can preferentially select different overlap configurations in $\mathrm{U}+\mathrm{U}$ collisions. We also show that $v_2$ vs multiplicity can be better described by models, such as gluon saturation or quark participant models, that eliminate the dependence of the multiplicity on the number of binary nucleon-nucleon collisions.

We present the calculations on a novel reorientation effect of deuteron attributed to isovector interaction in the nuclear field of heavy target nuclei. The correlation angle determined by the relative momentum vector of the proton and the neutron originating from the breakup deuteron, which is experimentally detectable, exhibits significant dependence on the isovector nuclear potential but is robust against the variation of the isoscaler sector. In terms of sensitivity and cleanness, the breakup reactions induced by the polarized deuteron beam at about $100\mathrm{MeV}/\mathrm{u}$ provide a more stringent constraint to the symmetry energy at subsaturation densities.

Five dimensional black hole solutions that describe the QCD crossover transition seen in $(2+1)$-flavor lattice QCD calculations at zero and nonzero baryon densities are used to obtain predictions for the baryon susceptibility, baryon conductivity, baryon diffusion constant, and thermal conductivity of the strongly coupled quark-gluon plasma in the range of temperatures $130\mathrm{MeV}\le T\le 300\mathrm{MeV}$ and baryon chemical potentials $0\le {\mu }_B\le 400\mathrm{MeV}$. Diffusive transport is predicted to be suppressed in this region of the QCD phase diagram, which is consistent with the existence of a critical end point at larger baryon densities. We also calculate the fourth-order baryon susceptibility at zero baryon chemical potential and find quantitative agreement with recent lattice results. The baryon transport coefficients computed in this Letter can be readily implemented in state-of-the-art hydrodynamic codes used to investigate the dense QGP currently produced at RHIC’s low energy beam scan.

We match the results for the subthreshold parameters of pion-nucleon scattering obtained from a solution of Roy-Steiner equations to chiral perturbation theory up to next-to-next-to-next-to-leading order, to extract the pertinent low-energy constants including a comprehensive analysis of systematic uncertainties and correlations. We study the convergence of the chiral series by investigating the chiral expansion of threshold parameters up to the same order and discuss the role of the $\mathrm{\Delta }(1232)$ resonance in this context. Results for the low-energy constants are also presented in the counting scheme usually applied in chiral nuclear effective field theory, where they serve as crucial input to determine the long-range part of the nucleon-nucleon potential as well as three-nucleon forces.

We report on the measurement of the first $2^{+}$ and $4^{+}$ states of ${}^{66}\mathrm{Cr}$ and ${}^{70,72}\mathrm{Fe}$ via in-beam $\gamma$-ray spectroscopy. The nuclei of interest were produced by $(p,2p)$ reactions at incident energies of $260\mathrm{MeV}/\text{nucleon}$. The experiment was performed at the Radioactive Isotope Beam Factory, RIKEN, using the DALI $2\gamma$-ray detector array and the novel MINOS device, a thick liquid hydrogen target combined with a vertex tracker. A low-energy plateau of $2_1^{+}$ and $4_1^{+}$ energies as a function of the neutron number was observed for $N\ge 38$ and $N\ge 40$ for even-even Cr and Fe isotopes, respectively. State-of-the-art shell model calculations with a modified Lenzi-Nowacki-Poves-Sieja (LNPS) interaction in the $pf{g}_{9/2}{d}_{5/2}$ valence space reproduce the observations. Interpretation within the shell model shows an extension of the island of inversion at $N=40$ for more neutron-rich isotopes towards $N=50$.

In the standard model, the weak interaction is formulated with a purely vector-axial-vector ($V\text{−}A$) structure. Without restriction on the chirality of the neutrino, the most general limits on tensor currents from nuclear $\beta$ decay are dominated by a single measurement of the $\beta \text{−}\overline{\nu }$ correlation in ${}^6\mathrm{He}$ $\beta$ decay dating back over a half century. In the present work, the $\beta \text{−}\overline{\nu }\text{−}\alpha$ correlation in the $\beta$ decay of ${}^8\mathrm{Li}$ and subsequent $\alpha$-particle breakup of the ${{}^8\mathrm{Be}}^{*}$ daughter was measured. The results are consistent with a purely $V\text{−}A$ interaction and in the case of couplings to right-handed neutrinos ($C_T=-C_T^{\prime }$) limits the tensor fraction to $|C_T/C_A{|}^2<0.011$ (95.5% C.L.). The measurement confirms the ${}^6\mathrm{He}$ result using a different nuclear system and employing modern ion-trapping techniques subject to different systematic uncertainties.

We numerically solve the ($2+1$)-dimensional effective kinetic theory of weak coupling QCD under longitudinal expansion, relevant for early stages of heavy-ion collisions. We find agreement with viscous hydrodynamics and classical Yang-Mills simulations in the regimes where they are applicable. By choosing initial conditions that are motivated by a color-glass-condensate framework, we find that for $Q_s=2\mathrm{GeV}$ and ${\alpha }_s=0.3$ the system is approximately described by viscous hydrodynamics well before $\tau \lesssim 1.0\mathrm{fm}/c$.