Azimuthal angular correlations of charged hadrons with respect to the axis of a reconstructed (trigger) jet in $\mathrm{Au}+\mathrm{Au}$ and $p+p$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ in STAR are presented. The trigger jet population in $\mathrm{Au}+\mathrm{Au}$ collisions is biased toward jets that have not interacted with the medium, allowing easier matching of jet energies between $\mathrm{Au}+\mathrm{Au}$ and $p+p$ collisions while enhancing medium effects on the recoil jet. The associated hadron yield of the recoil jet is significantly suppressed at high transverse momentum ($p_T^{\text{assoc}}$) and enhanced at low $p_T^{\text{assoc}}$ in 0%–20% central $\mathrm{Au}+\mathrm{Au}$ collisions compared to $p+p$ collisions, which is indicative of medium-induced parton energy loss in ultrarelativistic heavy-ion collisions.

Excited states in the neutron-rich $N=38$, 36 nuclei ${}^{60}\mathrm{Ti}$ and ${}^{58}\mathrm{Ti}$ were populated in nucleon-removal reactions from ${}^{61}\mathrm{V}$ projectiles at $90\mathrm{MeV}/\text{nucleon}$. The $\gamma$-ray transitions from such states in these Ti isotopes were detected with the advanced $\gamma$-ray tracking array GRETINA and were corrected event by event for large Doppler shifts ($v/c\sim 0.4$) using the $\gamma$-ray interaction points deduced from online signal decomposition. The new data indicate that a steep decrease in quadrupole collectivity occurs when moving from neutron-rich $N=36$, 38 Fe and Cr toward the Ti and Ca isotones. In fact, ${}^{58,60}\mathrm{Ti}$ provide some of the most neutron-rich benchmarks accessible today for calculations attempting to determine the structure of the potentially doubly magic nucleus ${}^{60}\mathrm{Ca}$.

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.

Gamow-Teller (GT) transitions in atomic nuclei are sensitive to both nuclear shell structure and effective residual interactions. The nuclear GT excitations were studied for the mass number $A=42$, 46, 50, and 54 “$f$-shell” nuclei in (${}^3\mathrm{He}$, $t$) charge-exchange reactions. In the ${}^{42}\mathrm{Ca}\to {}^{42}\mathrm{Sc}$ reaction, most of the GT strength is concentrated in the lowest excited state at 0.6 MeV, suggesting the existence of a low-energy GT phonon excitation. As $A$ increases, a high-energy GT phonon excitation develops in the 6–11 MeV region. In the ${}^{54}\mathrm{Fe}\to {}^{54}\mathrm{Co}$ reaction, the high-energy GT phonon excitation mainly carries the GT strength. The existence of these two GT phonon excitations are attributed to the 2 fermionic degrees of freedom in nuclei.

We report the first branching-ratio measurement of the superallowed $0^{+}\to 0^{+}\beta$ transition from ${}^{38}\mathrm{Ca}$. The result, 0.7728(16), leads to an $ft$ value of 3062.3(68) s with a relative precision of $\pm 0.2\%$. This makes possible a high-precision comparison of the $ft$ values for the mirror superallowed transitions, ${}^{38}\mathrm{Ca}{\to }^{38m}\mathrm{K}$ and ${}^{38m}\mathrm{K}\to {}^{38}\mathrm{Ar}$, which sensitively tests the isospin symmetry-breaking corrections required to extract $V_{ud}$, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, from superallowed $\beta$ decay. The result supports the corrections currently used and points the way to even tighter constraints on CKM unitarity.

The flow harmonics $v_{2,3}$ for charged hadrons are studied for a broad range of centrality selections and beam collision energies in $\mathrm{Au}+\mathrm{Au}$ ($\sqrt{s_{NN}}=7.7–200\mathrm{GeV}$) and $\mathrm{Pb}+\mathrm{Pb}$ ($\sqrt{s_{NN}}=2.76\mathrm{TeV}$) collisions. They validate the characteristic signature expected for the system size dependence of viscous damping at each collision energy studied. The extracted viscous coefficients that encode the magnitude of the ratio of shear viscosity to entropy density $\eta /s$ are observed to decrease to an apparent minimum as the collision energy is increased from $\sqrt{s_{NN}}=7.7$ to approximately 62.4 GeV; thereafter, they show a slow increase with $\sqrt{s_{NN}}$ up to 2.76 TeV. This pattern of viscous damping provides the first experimental constraint for $\eta /s$ in the temperature-baryon chemical potential ($T$, ${\mu }_B$) plane and could be an initial indication for decay trajectories that lie close to the critical end point in the phase diagram for nuclear matter.

We show that the statistics of fluctuation-driven initial-state anisotropies in proton-proton, proton nucleus and nucleus-nucleus collisions is to a large extent universal. We propose a simple parametrization for the probability distribution of the Fourier coefficient ${ϵ}_n$ in harmonic $n$, which is in good agreement with Monte Carlo simulations. Our results provide a simple explanation for the 4-particle cumulant of triangular flow measured in Pb-Pb collisions and for the 4-particle cumulant of elliptic flow recently measured in $p\text{−}\mathrm{Pb}$ collisions. Both arise as natural consequences of the condition that initial anisotropies are bounded by unity. We argue that the initial rms anisotropy in harmonic $n$ can be directly extracted from the measured ratio $v_n\{4\}/v_n\{2\}$: this gives direct access to a property of the initial density profile from experimental data. We also make quantitative predictions for the small lifting of degeneracy between $v_n\{4\}$, $v_n\{6\}$, and $v_n\{8\}$. If confirmed by future experiments, they will support the picture that long-range correlations observed in $p\text{−}\mathrm{Pb}$ collisions at the LHC originate from collective flow proportional to the initial anisotropy.

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.

The electromagnetic dipole strength below the neutron-separation energy has been studied for the xenon isotopes with mass numbers $A=124$, 128, 132, and 134 in nuclear resonance fluorescence experiments using the $\gamma \mathrm{ELBE}$ bremsstrahlung facility at Helmholtz-Zentrum Dresden-Rossendorf and the $\mathrm{HI}\gamma \mathrm{S}$ facility at Triangle Universities Nuclear Laboratory Durham. The systematic study gained new information about the influence of the neutron excess as well as of nuclear deformation on the strength in the region of the pygmy dipole resonance. The results are compared with those obtained for the chain of molybdenum isotopes and with predictions of a random-phase approximation in a deformed basis. It turned out that the effect of nuclear deformation plays a minor role compared with the one caused by neutron excess. A global parametrization of the strength in terms of neutron and proton numbers allowed us to derive a formula capable of predicting the summed $E1$ strengths in the pygmy region for a wide mass range of nuclides.

We identify a potential means to extract the ${}^{229g}\mathrm{Th}\to {}^{229m}\mathrm{Th}$ nuclear excitation energy from precision microwave spectroscopy of the $5F_{5/2,7/2}$ hyperfine manifolds in the ion ${{}^{229g}\mathrm{Th}}^{3+}$. The hyperfine interaction mixes this ground fine structure doublet with states of the nuclear isomer, introducing small but observable shifts to the hyperfine sublevels. We demonstrate how accurate atomic structure calculations may be combined with the measurement of the hyperfine intervals to quantify the effects of this mixing. Further knowledge of the magnetic dipole decay rate of the isomer, as recently reported, allows an indirect determination of the nuclear excitation energy.

Symmetry is an important and basic topic in physics. The similarity renormalization group theory provides a novel view to study the symmetries hidden in the Dirac Hamiltonian, especially for the deformed system. Based on the similarity renormalization group theory, the contributions from the nonrelativistic term, the spin-orbit term, the dynamical term, the relativistic modification of kinetic energy, and the Darwin term are self-consistently extracted from a general Dirac Hamiltonian and, hence, we get an accurate description for their dependence on the deformation. Taking an axially deformed nucleus as an example, we find that the self-consistent description of the nonrelativistic term, spin-orbit term, and dynamical term is crucial for understanding the relativistic symmetries and their breaking in a deformed nuclear system.

We present a new picture that the $\alpha$-linear-chain structure for ${}^{12}\mathrm{C}$ and ${}^{16}\mathrm{O}$ has one-dimensional $\alpha$ condensate character. The wave functions of linear-chain states that are described by superposing a large number of Brink wave functions have extremely large overlaps of nearly 100% with single Tohsaki-Horiuchi-Schuck-Röpke wave functions, which were proposed to describe the $\alpha$ condensed “gaslike” states. Although this new picture is different from the conventional idea of the spatial localization of $\alpha$ clusters, the density distributions are shown to have localized $\alpha$ clusters due to the inter-$\alpha$ Pauli repulsion.

Excited states in ${}^{102}\mathrm{Rh}$, populated in the fusion-evaporation reaction ${}^{94}\mathrm{Zr}({}^{11}\mathrm{B},3\mathrm{n}){}^{102}\mathrm{Rh}$ at a beam energy of 36 MeV, were studied using the Indian National Gamma Array spectrometer at Inter University Accelerator Center, New Delhi. The angular correlations and the electromagnetic character of some of the gamma-ray transitions observed were investigated in detail. A new chiral candidate sister band was found. Lifetimes of exited states in both chiral candidate bands of ${}^{102}\mathrm{Rh}$ were measured for the first time in the $A\sim 100$ mass region by means of the Doppler-shift attenuation technique. The derived reduced transition probabilities are compared to the predictions of the two quasiparticles plus triaxial rotor model. Both experimental results and calculations do not support the presence of static chirality in ${}^{102}\mathrm{Rh}$.

Both charged hadrons and $D$ mesons are considered to be excellent probes of QCD matter created in ultrarelativistic heavy ion collisions. Surprisingly, recent experimental observations at LHC show the same jet suppression for these two probes, which—contrary to pQCD expectations—may suggest similar energy losses for light quarks and gluons in the QCD medium. We here use our recently developed energy loss formalism in a finite-size dynamical QCD medium to analyze this phenomenon that we denote as the “heavy flavor puzzle at LHC.” We show that this puzzle is a consequence of an unusual combination of the suppression and fragmentation patterns and, in fact, does not require invoking the same energy loss for light partons. Furthermore, we show that this combination leads to a simple relationship between the suppressions of charged hadrons and $D$ mesons and the corresponding bare quark suppressions. Consequently, a coincidental matching of jet suppression and fragmentation allows considerably simplifying the interpretation of the corresponding experimental data.

Energies and spectroscopic factors of the first $7/2^{-}$, $3/2^{-}$, $1/2^{-}$, and $5/2^{-}$ states in the ${}^{35}{\mathrm{Si}}_{21}$ nucleus were determined by means of the ($d$, $p$) transfer reaction in inverse kinematics at GANIL using the MUST2 and EXOGAM detectors. By comparing the spectroscopic information on the ${}^{35}\mathrm{Si}$ and ${}^{37}\mathrm{S}$ isotones, a reduction of the $p_{3/2}\text{−}{p}_{1/2}$ spin-orbit splitting by about 25% is proposed, while the $f_{7/2}\text{−}{f}_{5/2}$ spin-orbit splitting seems to remain constant. These features, derived after having unfolded nuclear correlations using shell model calculations, have been attributed to the properties of the two-body spin-orbit interaction, the amplitude of which is derived for the first time in an atomic nucleus. The present results, remarkably well reproduced by using several realistic nucleon-nucleon forces, provide a unique touchstone for the modeling of the spin-orbit interaction in atomic nuclei.