We study dependence of jet quenching on matter density, using “tomography” of the fireball provided by RHIC data on azimuthal anisotropy $v_2$ of high $p_t$ hadron yield at different centralities. Slicing the fireball into shells with constant (entropy) density, we derive a “layer-wise geometrical limit” $v_2^{\max }$ which is indeed above the data $v_2<v_2^{\max }$. Interestingly, the limit is reached only if quenching is dominated by shells with the entropy density exactly in the near-$T_c$ region. We show two models that simultaneously describe the high $p_t$ $v_2$ and $R_{A\mathrm{\text{−}}A}$ data and conclude that such a description can be achieved only if the jet quenching is few times stronger in the near-$T_c$ region relative to QGP at $T>T_c$. One possible reason for such enhancement may be recent indications that the near-$T_c$ region is a magnetic plasma of relatively light color-magnetic monopoles.

A lifetime measurement of the excited states in the neutron-rich isotope ${}^{13}\mathrm{B}$ has been performed using the ${}^7\mathrm{Li}({}^7\mathrm{Li},p){}^{13}\mathrm{B}$ reaction. An anomalously long mean lifetime of 1.3(3) ps was found for the excited state at 3.53 MeV, giving the upper limits of the transition strengths to the ground state: $B(M1)=7.2\times {10}^{-4}\mathrm{\text{Weisskopf unit}}$ (W.u.) and $B(E2)=0.81\mathrm{W}.\mathrm{u}.$. The hindered transition strengths indicate significant intruder configurations for the excited state, coexisting with the normal ground state. The data are well explained by recent shell-model calculations, which suggest $J^{\pi }=3/2^{-}$ for the 3.53-MeV state with the dominant intruder ($\nu 2p2h$) configuration.

The gluonic contribution to the nuclear modification factor $R_{AA}$ is investigated for central $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s}=200A\mathrm{GeV}$ employing a perturbative QCD-based parton cascade including radiative processes. A flat quenching pattern is found up to transverse momenta of 30 GeV, which is slightly smaller compared with results from the Gyulassy-Levai-Vitev formalism. We demonstrate that the present microscopic transport description provides a challenging means of investigating both jet quenching and a strong buildup of elliptic flow in terms of the same standard perturbative QCD interactions.

The effect of initial correlations between nucleons on the nuclear breakup mechanism is studied. A quantum transport theory which extends the standard mean-field approach is developed to incorporate short range pairing correlation as well as direct nucleon-nucleon collisions. A time evolution of the nuclear breakup from a correlated system leading to the emission of two particles to the continuum is performed. We show that initial correlations have strong influence on relative angles between particles emitted in coincidence. The present qualitative study indicates that nuclear breakup might be a tool to infer the residual interaction between nucleons in the nuclear medium.

We show that if a flavorless vector meson remains bound after deconfinement, and if its limiting velocity in the quark-gluon plasma is subluminal, then this meson produces a distinct peak in the spectrum of thermal photons emitted by the plasma. We also demonstrate that this effect is a universal property of all strongly coupled, large-$N_c$ plasmas with a gravity dual. For the $J/\psi$, the corresponding peak lies between 3 and 5 GeV and could be observed in heavy-ion collisions at the LHC.

The cross section for inclusive multipion production in the $pp\to ppX$ reaction was measured at COSY-ANKE at four beam energies, 0.8, 1.1, 1.4, and 2.0 GeV, for low excitation energy in the final $pp$ system, such that the diproton quasiparticle is in the ${}^{1}S_0$ state. At the three higher energies, the missing-mass $M_X$ spectra show a strong enhancement at low $M_X$, corresponding to an Abashian-Booth-Crowe effect that moves steadily to larger values as the energy is increased. Despite the missing-mass structure looking very different at 0.8 GeV, the variation with $M_X$ and beam energy are consistent with two-pion production being mediated through the excitation of two $\Delta (1232)$ isobars, coupled to $S$ and $D$ states of the initial $pp$ system. There is no sign of any resonancelike structure in the energy dependence of the type recently observed for the $pn\to d{\pi }^0{\pi }^0$ total cross section.

The dependence of fission barriers on the excitation energy of the compound nucleus impacts the survival probability of superheavy nuclei synthesized in heavy-ion fusion reactions. In this work, we investigate the isentropic fission barriers by means of the self-consistent nuclear density functional theory. The relationship between isothermal and isentropic descriptions is demonstrated. Calculations have been carried out for ${}^{264}\mathrm{Fm}$, ${}^{272}\mathrm{Ds}$, ${}^{278}112$, ${}^{292}114$, and ${}^{312}124$. For nuclei around ${}^{278}112$ produced in “cold-fusion” reactions, we predict a more rapid decrease of fission barriers with excitation energy as compared to the nuclei around ${}^{292}114$ synthesized in “hot-fusion” experiments. This is explained in terms of the difference between the ground-state and saddle-point temperatures. The effect of the particle gas is found to be negligible in the range of temperatures studied.

We report on the first in-beam $\gamma$-ray spectroscopy study of the very neutron-rich nucleus ${}^{46}\mathrm{S}$. The $N=30$ isotones ${}^{46}\mathrm{S}$ and ${}^{48}\mathrm{Ar}$ were produced in a novel way in two steps that both necessarily involve nucleon exchange and neutron pickup reactions ${}^9\mathrm{Be}({}^{48}\mathrm{Ca},{}^{48}\mathrm{K})X$ followed by ${}^9\mathrm{Be}({}^{48}\mathrm{K},{}^{48}\mathrm{Ar}+\gamma )X$ at $85.7\mathrm{MeV}/\mathrm{u}$ midtarget energy and ${}^9\mathrm{Be}({}^{48}\mathrm{Ca},{}^{46}\mathrm{Cl})X$ followed by ${}^9\mathrm{Be}({}^{46}\mathrm{Cl},{}^{46}\mathrm{S}+\gamma )X$ at $87.0\mathrm{MeV}/\mathrm{u}$ midtarget energy, respectively. The results are compared to large-scale shell-model calculations in the $sd\mathrm{\text{−}}pf$ shell using the SDPF-NR effective interaction and $Z$-dependent modifications.

We suggest using net-baryon rapidity distributions in central relativistic heavy-ion collisions at energies reached at the CERN Super Proton Synchrotron, BNL Relativistic Heavy-Ion Collider (RHIC), and CERN LHC in order to probe saturation physics. Within the color glass condensate framework based on small-coupling QCD, net-baryon rapidity distributions are shown to exhibit geometric scaling. In a comparison with RHIC data in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=62.4\mathrm{GeV}$ and 200 GeV the gradual approach to the gluon saturation regime is investigated. Predictions for net-baryon rapidity spectra and the mean rapidity loss in central $\mathrm{Pb}+\mathrm{Pb}$ collisions at LHC energies of $\sqrt{s_{NN}}=5.52\mathrm{TeV}$ are made.

The $K^0$ meson production by ${\pi }^{-}$ mesons of $1.15\mathrm{GeV}/c$ momentum on C, Al, Cu, Sn, and Pb nuclear targets was measured with the FOPI spectrometer at the Schwer-Ionen-Synchrotron accelerator of GSI. Inclusive production cross sections and the momentum distributions of $K^0$ mesons are compared to scaled elementary production cross sections and to predictions of theoretical models describing the in-medium production of kaons. The data represent a new reference for those models, which are widely used for interpretation of the strangeness production in heavy-ion collisions. The presented results demonstrate the sensitivity of the kaon production to the reaction amplitudes inside nuclei and point to the existence of a repulsive $KN$ potential of $20\pm 5\mathrm{MeV}$ at normal nuclear matter density.

Both components of the transverse polarization of electrons (${\sigma }_{T_1}$, ${\sigma }_{T_2}$) emitted in the $\beta$-decay of polarized, free neutrons have been measured. The $T$-odd, $P$-odd correlation coefficient quantifying ${\sigma }_{T_2}$, perpendicular to the neutron polarization and electron momentum, was found to be $R=0.008\pm 0.015\pm 0.005$. This value is consistent with time reversal invariance and significantly improves limits on the relative strength of imaginary scalar couplings in the weak interaction. The value obtained for the correlation coefficient associated with ${\sigma }_{T_1}$, $N=0.056\pm 0.011\pm 0.005$, agrees with the Standard Model expectation, providing an important sensitivity test of the experimental setup.

Ultrarelativistic heavy-ion collisions at the Brookhaven National Laboratory Relativistic Heavy Ion Collider (RHIC) are thought to have produced a state of matter called the quark-gluon plasma, characterized by a very small shear-viscosity to entropy-density ratio $\eta /s$, near the lower bound predicted for that quantity by anti–de Sitter space/conformal field theory methods. As the produced matter expands and cools, it evolves through a phase described by a hadron gas with rapidly increasing $\eta /s$. We calculate $\eta /s$ as a function of temperature in this phase both in and out of chemical equilibrium and find that its value poses a challenge for viscous relativistic hydrodynamics, which requires small values of $\eta /s$ in order to successfully describe the collective flow observables at the RHIC. We therefore conclude that the origin of the low viscosity matter at the RHIC must be in the partonic phase of the reaction.

Many masses, particularly the masses of unstable nuclei, are measured with ions in Penning traps by determining the frequency of a driving force that most efficiently couples two of the three motions of trapped ions. A missing explanation of why such sideband mass spectroscopy works, contrary to simple estimates, begins with the established Brown-Gabrielse invariance theorem.

We present an ab initio calculation of the longitudinal electron scattering response function off ${}^4\mathrm{He}$ with two- and three-nucleon forces and compare to experimental data. The full four-body continuum dynamics is considered via the Lorentz integral transform method. The importance of the final-state interaction is shown at various energies and momentum transfers $q$. The three-nucleon force reduces the quasielastic peak by 10% for $q$ between 300 and $500\mathrm{MeV}/c$. Its effect increases significantly at lower $q$, up to about 40% at $q=100\mathrm{MeV}/c$. At very low $q$, however, data are missing.

A $\gamma$-ray spectroscopy study of ${}^{26g}\mathrm{Al}+p$ resonant states in ${}^{27}\mathrm{Si}$ is presented. Excitation energies were measured with improved precision and first spin-parity assignments made for excited states in ${}^{27}\mathrm{Si}$ above the proton threshold. The results indicate the presence of low-lying resonances with $l_p=0$ and $l_p=2$ captures that could strongly influence the ${}^{26g}\mathrm{Al}(p,\gamma ){}^{27}\mathrm{Si}$ reaction rate at low stellar temperatures, found in low-mass asymptotic giant branch (AGB), intermediate-mass AGB, super AGB, and Wolf-Rayet stars.

Six proton-emitting states in ${}^{19}\mathrm{Ne}$ were studied through the inelastic scattering reaction $\mathrm{H}({}^{19}\mathrm{Ne},p){}^{19}\mathrm{Ne}^{*}(p){}^{18}\mathrm{F}$. Their energies and widths were derived from the protons detected at zero degree, while proton-proton angular correlations between the detector at zero degree and a segmented annular detector were used to determine their spin value. In addition to the known states, a new broad $J=\frac{1}{2}$ resonance has been evidenced at $E_x\approx 7.9\mathrm{MeV}$, $\approx 1.45\mathrm{MeV}$ above the proton emission threshold. By introducing this resonance, the ${}^{18}\mathrm{F}(p,\alpha ){}^{15}\mathrm{O}$ destruction rate in novae is significantly enhanced. This reduces the chance to observe the cosmic $\gamma$-ray emission of ${}^{18}\mathrm{F}$ from novae in space telescopes.

The radiative strength function of ${}^{117}\mathrm{Sn}$ has been measured up to the neutron separation energy using the (${}^3\mathrm{He}$, ${}^3\mathrm{He}^{\prime }\gamma$) reaction. An increase in the slope of the strength function around $E_{\gamma }=4.5\mathrm{MeV}$ indicates the onset of a resonancelike structure, giving a significant enhancement of the radiative strength function compared to standard models in the energy region $4.5\le E_{\gamma }\le 8.0\mathrm{MeV}$. For the first time, the functional form of this resonancelike structure has been measured in an odd tin nucleus below neutron threshold in the quasicontinuum region.

We present a new Skyrme-Hartree-Fock-Bogoliubov nuclear-mass model in which the contact-pairing force is constructed from microscopic pairing gaps of symmetric nuclear matter and neutron matter calculated from realistic two- and three-body forces, with medium-polarization effects included. With the pairing being treated more realistically than in any of our earlier models, the rms deviation with respect to essentially all the available mass data falls to 0.581 MeV, the best value ever found within the mean-field framework. Since our Skyrme force is also constrained by the properties of pure neutron matter, this new model is particularly well suited for application to astrophysical problems involving a neutron-rich environment, such as the elucidation of the $r$ process of nucleosynthesis, and the description of supernova cores and neutron-star crusts.

We consider a novel mechanism for $J/\psi$ production in nuclear collisions arising due to the high density of gluons. The resulting $J/\psi$ production cross section is evaluated as a function of rapidity and centrality. We compute the nuclear modification factor and show that the rapidity distribution of the produced $J/\psi$’s is significantly more narrow in $AA$ collisions due to the gluon saturation effects. Our results indicate that gluon saturation in the colliding nuclei is a significant source of $J/\psi$ suppression and can explain the experimentally observed rapidity and centrality dependencies of the effect.

The rate of the ${}^{17}\mathrm{F}(p,\text{}\gamma ){}^{18}\mathrm{Ne}$ reaction is important in various astrophysical events. A previous ${}^{17}\mathrm{F}(p,\text{}p){}^{17}\mathrm{F}$ measurement identified a $3^{+}$ state providing the strongest resonance contribution, but the resonance strength was unknown. We have directly measured the ${}^{17}\mathrm{F}(p,\text{}\gamma ){}^{18}\mathrm{Ne}$ reaction using a mixed beam of ${}^{17}\mathrm{F}$ and ${}^{17}\mathrm{O}$ at ORNL. The resonance strength for the $3^{+}$ resonance in ${}^{18}\mathrm{Ne}$ was found to be $\omega \gamma =33\pm 14(\mathrm{stat})\pm 17(\mathrm{syst})\mathrm{meV}$, corresponding to a $\gamma$ width of ${\Gamma }_{\gamma }=56\pm 24(\mathrm{stat})\pm 30(\mathrm{syst})\mathrm{meV}$. An upper limit on the direct capture of $S(E)\le 65\mathrm{keV}\mathrm{b}$ was determined at an energy of 800 keV.