Lifetimes of states in the ground-state bands of ${}^{70}\mathrm{Se}$ and ${}^{72}\mathrm{Se}$ were measured using the recoil-distance Doppler shift method. The results deviate significantly from earlier measurements, requiring a revision of the conclusions drawn from a recent Coulomb excitation experiment concerning the shape of ${}^{70}\mathrm{Se}$. The new results lead to a coherent picture of shape coexistence in the neutron-deficient selenium and krypton isotopes. The coexistence and evolution of oblate and prolate shapes in this mass region is for the first time consistently described by new Hartree-Fock-Bogolyubov-based configuration-mixing calculations which were performed using the Gogny D1S interaction.

We calculate the medium dilepton yield from a quark-gluon plasma which has a time-dependent local momentum-space anisotropy. A phenomenological model for the hard momentum scale, $p_{\mathrm{hard}}(\tau )$, and plasma anisotropy parameter, $\xi (\tau )$, is constructed which interpolates between longitudinal free streaming at early times ($\tau \ll {\tau }_{\mathrm{iso}}$) and ideal hydrodynamic at late times ($\tau \gg {\tau }_{\mathrm{iso}}$). We show that high-energy dilepton production is sensitive to the plasma isotropization time, ${\tau }_{\mathrm{iso}}$, and can therefore be used to experimentally determine the time of onset for hydrodynamic expansion of a quark-gluon plasma and the magnitude of expected early-time momentum-space anisotropies.

A mechanism, consistent with color confinement, for the transition between perturbative and physical vacua during the gradual crossover from the hadronic to partonic phase is proposed. The essence of this mechanism is the appearance and growing up of a kind of grape-shape perturbative vacuum inside the physical one. A percolation model based on simple dynamics for parton delocalization is constructed to exhibit this mechanism. The crossover from hadronic matter to sQGP (strongly coupled quark-gluon plasma) as well as the transition from sQGP to weakly coupled quark-gluon plasma with increasing temperature is successfully described by using this model.

We calculate and compare bremsstrahlung and collisional energy loss of hard partons traversing a quark-gluon plasma. Our treatment of both processes is complete at leading order in the coupling and accounts for the probabilistic nature of the jet energy loss. We find that the nuclear modification factor $R_{AA}$ for neutral ${\pi }^0$ production in heavy ion collisions is sensitive to the inclusion of collisional and radiative energy loss contributions while the averaged energy loss only slightly increases if collisional energy loss is included for parent parton energies $E\gg T$. These results are important for the understanding of jet quenching in $\mathrm{Au}+\mathrm{Au}$ collisions at $200A\mathrm{GeV}$ at the Relativistic Heavy Ion Collider (RHIC). Comparison with data is performed applying the energy loss calculation to a relativistic ideal ($3+1$)-dimensional hydrodynamic description of the thermalized medium formed at RHIC.

A high-precision direct Penning trap mass measurement has revealed a 0.5-MeV deviation of the binding energy of ${}^{134}\mathrm{Sn}$ from the currently accepted value. The corrected mass assignment of this neutron-rich nuclide restores the neutron-shell gap at $N=82$, previously considered to be a case of “shell quenching.” In fact, the new shell gap value for the short-lived ${}^{132}\mathrm{Sn}$ is larger than that of the doubly magic ${}^{48}\mathrm{Ca}$ which is stable. The $N=82$ shell gap has considerable impact on fission recycling during the $r$ process. More generally, the new finding has important consequences for microscopic mean-field theories which systematically deviate from the measured binding energies of closed-shell nuclides.

A new lowest order QED calculation for BNL Relativistic Heavy-Ion Collider $e^{+}{e}^{-}$ pair production has been carried out with a phenomenological treatment of the Coulomb dissociation of the heavy-ion nuclei observed in the STAR ZDC triggers. The lowest order QED result for the experimental acceptance is nearly 2 standard deviations larger than the STAR data. A corresponding higher-order QED calculation is consistent with the data.

We present shell model calculations for the beta decay of ${}^{14}\mathrm{C}$ to the ${}^{14}\mathrm{N}$ ground state, treating the states of the $A=14$ multiplet as two $0p$ holes in an ${}^{16}\mathrm{O}$ core. We employ low-momentum nucleon-nucleon ($NN$) interactions derived from the realistic Bonn-B potential and find that the Gamow-Teller (GT) matrix element is too large to describe the known lifetime. By using a modified version of this potential that incorporates the effects of Brown-Rho scaling medium modifications, we find that the GT matrix element vanishes for a nuclear density around 85% that of nuclear matter. We find that the splitting between the $(J^{\pi },T)=(1^{+},0)$ and $(J^{\pi },T)=(0^{+},1)$ states in ${}^{14}\mathrm{N}$ is improved using the medium-modified Bonn-B potential and that the transition strengths from excited states of ${}^{14}\mathrm{C}$ to the ${}^{14}\mathrm{N}$ ground state are compatible with recent experiments.

We report a high statistics measurement of ${\rm Y}$ production with an $800\mathrm{GeV}/c$ proton beam on hydrogen and deuterium targets. The dominance of the gluon-gluon fusion process for ${\rm Y}$ production at this energy implies that the cross section ratio, $\sigma (p+d\to {\rm Y})/2\sigma (p+p\to {\rm Y})$, is sensitive to the gluon content in the neutron relative to that in the proton. Over the kinematic region $0<x_F<0.6$, this ratio is found to be consistent with unity, in striking contrast to the behavior of the Drell-Yan cross section ratio $\sigma (p+d{)}_{\mathrm{DY}}/2\sigma (p+p{)}_{\mathrm{DY}}$. This result shows that the gluon distributions in the proton and neutron are very similar. The ${\rm Y}$ production cross sections are also compared with the $p+d$ and $p+\mathrm{Cu}$ cross sections from earlier measurements.

We study in this Letter the neutrinoless double beta decay nuclear matrix elements (NME’s) in the framework of the interacting shell model. We analyze them in terms of the total angular momentum of the decaying neutron pair and as a function of the seniority truncations in the nuclear wave functions. This point of view turns out to be very adequate to gauge the accuracy of the NME’s predicted by different nuclear models. In addition, it gives back the protagonist role in this process to the pairing interaction, the one which is responsible for the very existence of double beta decay emitters. We show that low seniority approximations, comparable to those implicit in the quasiparticle RPA in a spherical basis, tend to overestimate the NME’s in several decays.

We compute the momentum diffusion coefficient of a heavy quark in a hot QCD plasma, to next-to-leading order in the weak-coupling expansion. Corrections arise at $\mathcal{O}(g_s)$; physically they represent interference between overlapping scatterings, as well as soft, electric scale ($p\sim gT$) gauge field physics, which we treat using the hard thermal loop effective theory. In 3-color, 3-flavor QCD, the momentum diffusion constant of a fundamental representation heavy quark at next-to-leading order is $\kappa =\frac{16\pi }{3}{\alpha }_s^2{T}^3(\ln \frac{1}{g_s}+0.07428+1.9026g_s)$. The convergence of the perturbative expansion is poor.

We point out the possibility of the partial conservation of the seniority quantum number when most eigenstates are mixed in seniority but some remain pure. This situation occurs in nuclei for the $g_{9/2}$ and $h_{9/2}$ shells where it is at the origin of the existence of seniority isomers in the ruthenium and palladium isotopes. It also occurs for $f$ bosons.

The application of superscaling ideas to predict neutral-current (NC) quasielastic (QE) neutrino cross sections is investigated. The relativistic impulse approximation (RIA) using the same relativistic mean field potential (RMF) for both initial and final nucleons — a model that reproduces the experimental $(e,e^{\prime })$ scaling function — is used to illustrate our findings. While NC reactions are apparently not well suited for scaling analyses, to a large extent, the RIA-RMF predictions do exhibit superscaling. Independence of the scaled response on the nuclear species is very well fulfilled. The RIA-RMF NC superscaling function is in good agreement with the experimental $(e,e^{\prime })$ one. The idea that electroweak processes can be described with a universal scaling function, provided that mild restrictions on the kinematics are assumed, is shown to be valid.

The recently discovered coexistence of multifragmentation and residue production for the same total transverse energy of light charged particles, which has been dubbed bimodality like it has been introduced in the framework of equilibrium thermodynamics, can be well reproduced in numerical simulations of heavy ion reactions. A detailed analysis shows that fluctuations (introduced by elementary nucleon-nucleon collisions) determine which of the exit states is realized. Thus, we can identify bifurcation in heavy ion reactions as a critical phenomenon. Also the scaling of the coexistence region with beam energy is well reproduced in these results from the quantum molecular dynamics simulation program.

The isoscalar giant monopole resonance (GMR) and giant quadrupole resonance (GQR) have been measured in the ${}^{56}\mathrm{Ni}$ unstable nucleus by inducing the ${}^{56}\mathrm{Ni}(d,d^{\prime })$ reaction at $50A\mathrm{MeV}$ in the Maya active target at the GANIL facility. The GMR and GQR centroids are measured at $19.3\pm 0.5\mathrm{MeV}$ and $16.2\pm 0.5\mathrm{MeV}$, respectively. The corresponding angular distributions are extracted from 3° to 7°. A multipole decomposition analysis using distorted wave Born approximation with random phase approximation transition densities shows that both the GMR and the GQR exhaust a large fraction of the energy-weighted sum rule. The demonstration of this new method opens a broad range of giant resonance studies at intermediate-energy radioactive beam facilities.

The observation of neutrino oscillations is clear evidence for physics beyond the standard model. To make precise measurements of this phenomenon, neutrino oscillation experiments, including MiniBooNE, require an accurate description of neutrino charged current quasielastic (CCQE) cross sections to predict signal samples. Using a high-statistics sample of ${\nu }_{\mu }$ CCQE events, MiniBooNE finds that a simple Fermi gas model, with appropriate adjustments, accurately characterizes the CCQE events observed in a carbon-based detector. The extracted parameters include an effective axial mass, $M_A^{\mathrm{eff}}=1.23\pm 0.20\mathrm{GeV}$, that describes the four-momentum dependence of the axial-vector form factor of the nucleon, and a Pauli-suppression parameter, $\kappa =1.019\pm 0.011$. Such a modified Fermi gas model may also be used by future accelerator-based experiments measuring neutrino oscillations on nuclear targets.

We show that the enhancement of the saturation scale in large nuclei relative to the proton is significantly influenced by the effects of quantum evolution and the impact parameter dependence of dipole cross sections in high energy QCD. We demonstrate that there is a strong $A$ dependence in diffractive deeply inelastic scattering and discuss its sensitivity to the measurement of the recoil nucleus.

The NA60 experiment at the CERN SPS has studied low-mass dimuon production in $158A\mathrm{GeV}$ In-In collisions. An excess of pairs above the known meson decays has been reported before. We now present precision results on the associated transverse momentum spectra. The slope parameter $T_{\mathrm{eff}}$ extracted from the spectra rises with dimuon mass up to the $\rho$, followed by a sudden decline above. While the initial rise is consistent with the expectations for radial flow of a hadronic decay source, the decline signals a transition to an emission source with much smaller flow. This may well represent the first direct evidence for thermal radiation of partonic origin in nuclear collisions.

The spallation of ${}^{56}\mathrm{Fe}$ in collisions with hydrogen at $1A\mathrm{GeV}$ has been studied in inverse kinematics with the large-aperture setup SPALADIN at GSI. Coincidences of residues with low-center-of-mass kinetic energy light particles and fragments have been measured allowing the decomposition of the total reaction cross section into the different possible deexcitation channels. Detailed information on the evolution of these deexcitation channels with excitation energy has also been obtained. The comparison of the data with predictions of several deexcitation models coupled to the INCL4 intranuclear cascade model shows that only GEMINI can reasonably account for the bulk of collected results, indicating that in a light system with no compression and little angular momentum, multifragmentation might not be necessary to explain the data.

We investigate possible mass shift and width broadening of $J/\psi$ in hot gluonic matter using QCD sum rules. Input values of gluon condensates at finite temperature are extracted from lattice QCD data for the energy density and pressure. Although stability of the moment ratio is achieved only up to $T/T_c\simeq 1.05$, the gluon condensates cause a decrease of the moment ratio, which results in a change of the spectral properties. Using the Breit-Wigner form for the phenomenological side, we find that the mass shift of $J/\psi$ just above $T_c$ can reach maximally 200 MeV and the width can broaden to dozens of MeV.

The lightest isotope of Bh was produced in the new ${}^{209}\mathrm{Bi}({}^{52}\mathrm{Cr},n){}^{260}\mathrm{Bh}$ reaction at the Lawrence Berkeley National Laboratory’s 88-Inch Cyclotron. Positive identification was made by observation of eight correlated alpha particle decay chains in the focal plane detector of the Berkeley Gas-Filled Separator. ${}^{260}\mathrm{Bh}$ decays with a ${35}_{-9}^{+19}\mathrm{ms}$ half-life by alpha particle emission mainly by a group at 10.16 MeV. The measured cross section of ${59}_{-20}^{+29}\mathrm{pb}$ is compared to model predictions. The influence of the $N=152$ and $Z=108$ shells on alpha decay properties is discussed.