We calculate the ground-state energy of ${}^4\mathrm{He}$, ${}^8\mathrm{He}$, ${}^{16}\mathrm{O}$, and ${}^{40}\mathrm{Ca}$ using the auxiliary field diffusion Monte Carlo method in the fixed-phase approximation and the Argonne $v_6^{\prime }$ interaction which includes a tensor force. Comparison of our light nuclei results to those of Green’s function Monte Carlo calculations shows the accuracy of our method for both open and closed-shell nuclei. We also apply it to ${}^{16}\mathrm{O}$ and ${}^{40}\mathrm{Ca}$ to show that quantum Monte Carlo methods are now applicable to larger nuclei.

We describe a new method to treat low-energy scattering problems in few-nucleon systems, and we apply it to the five-body case of neutron-alpha scattering. The method allows precise calculations of low-lying resonances and their widths. We find that a good three-nucleon interaction is crucial to obtain an accurate description of neutron-alpha scattering.

The energies of the excited states in very neutron-rich ${}^{42}\mathrm{S}\mathrm{i}$ and ${}^{41,43}\mathrm{P}$ have been measured using in-beam $\gamma$-ray spectroscopy from the fragmentation of secondary beams of ${}^{42,44}\mathrm{S}$ at $39A\mathrm{MeV}$. The low $2^{+}$ energy of ${}^{42}\mathrm{S}\mathrm{i}$, 770(19) keV, together with the level schemes of ${}^{41,43}\mathrm{P}$, provides evidence for the disappearance of the $Z=14$ and $N=28$ spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that ${}^{42}\mathrm{S}\mathrm{i}$ is best described as a well-deformed oblate rotor.

The first data on the relative single-particle energies outside the doubly magic ${}^{100}\mathrm{Sn}$ nucleus were obtained. A prompt $171.7(6)\mathrm{keV}$ $\gamma$-ray transition was correlated with protons emitted following the $\beta$ decay of ${}^{101}\mathrm{Sn}$ and is interpreted as the transition between the single-neutron $g_{7/2}$ and $d_{5/2}$ orbitals in ${}^{101}\mathrm{Sn}$. This observation provides a stringent test of current nuclear structure models. The measured $\nu g_{7/2}\mathrm{\text{−}}\nu d_{5/2}$ energy splitting is compared with values calculated using mean-field nuclear potentials and is used to calculate low-energy excited states in light Sn isotopes in the framework of the shell model. The correlation technique used in this work offers possibilities for future, more extensive spectroscopy near ${}^{100}\mathrm{Sn}$.

Gamma-ray transitions have been identified for the first time in the extremely neutron-deficient ($N=Z+2$) nucleus ${}^{110}\mathrm{Xe}$, and the energies of the three lowest excited states in the ground-state band have been deduced. The results establish a breaking of the normal trend of increasing first excited $2^{+}$ and $4^{+}$ level energies as a function of the decreasing neutron number as the $N=50$ major shell gap is approached for the neutron-deficient Xe isotopes. This unusual feature is suggested to be an effect of enhanced collectivity, possibly arising from isoscalar $n\mathrm{\text{−}}p$ interactions becoming increasingly important close to the $N=Z$ line.

We give recursive formulae for the exact removal of the contribution of the center-of-mass spurious states from the fixed-spin and parity nuclear level density found in shell-model calculations, provided the total level density for restricted configurations is known. The method is valid for a large class of problems using a harmonic oscillator basis. Using our earlier methods based on statistical spectroscopy that utilize the centroids and widths for a restricted class of fixed-spin configurations, such as $N\hslash \omega$ excitations, one can calculate very accurately level densities free of spurious states. The approach is applicable to other fermion and boson systems trapped by an oscillator potential.

The reaction ${}^2\mathrm{H}(e,e^{\prime }p)n$ has been studied with full kinematic coverage for photon virtuality $1.75<Q^2<5.5{\mathrm{GeV}}^2$. Comparisons of experimental data with theory indicate that for very low values of neutron recoil momentum ($p_n<100\mathrm{MeV}/c$) the neutron is primarily a spectator and the reaction can be described by the plane-wave impulse approximation. For $100<p_n<750\mathrm{MeV}/c$, proton-neutron rescattering dominates the cross section, while $\Delta$ production followed by the $N\Delta \to NN$ transition is the primary contribution at higher momenta.

We discuss how to obtain the nonrelativistic limit of a self-consistent relativistic effective field theory for dynamic problems. It is shown that the standard $v/c$ expansion yields Galilean invariance only to first order in $v/c$, whereas second order is required to obtain important contributions such as the spin-orbit force. We propose a modified procedure which is a mapping rather than a strict $v/c$ expansion.

Off-energy-shell effects in $p-p$ scattering have been investigated at $p-p$ relative energies from 600 down to 80 keV applying the Trojan horse method (THM) to the $p+d\to p+p+n$ reaction at 5 MeV. In contrast with the on-energy-shell case, no Coulomb-nuclear interference minimum has been found in the extracted THM $p-p$ cross section, due to the suppression of the Coulomb amplitude as predicted by the half-off-energy shell calculations. This hypothesis is strengthened by the agreement between THM $p-p$ data and calculated on-energy-shell $n+n$, $n+p$ and nuclear $p+p$ cross sections.

The electron-capture (EC) decay rate of ${}^7\mathrm{Be}$ in ${\mathrm{C}}_{60}$ at the temperature of liquid helium ($T=5\mathrm{K}$) was measured and compared with the rate in Be metal at $T=293\mathrm{K}$. We found that the half-life of ${}^7\mathrm{Be}$ in endohedral ${\mathrm{C}}_{60}$ (${}^7\mathrm{Be}@{\mathrm{C}}_{60}$) at a temperature close to $T=5\mathrm{K}$ is $52.47\pm 0.04\mathrm{d}$, a value that is 0.34% faster than that at $T=293\mathrm{K}$. In this environment, the half-life of ${}^7\mathrm{Be}$ is nearly 1.5% faster than that inside Be metal at room temperature ($T=293\mathrm{K}$). We then interpreted our observations in terms of calculations of the electron density at the ${}^7\mathrm{Be}$ nucleus position inside the ${\mathrm{C}}_{60}$; further, we estimate theoretically the temperature dependence (at $T=0\mathrm{K}$ and 293 K) of the electron density at the Be nucleus position in the stable center inside ${\mathrm{C}}_{60}$. The theoretical estimates were almost in agreement with the experimental observations.

This Letter presents measurements of the elliptic flow of charged particles as a function of pseudorapidity and centrality from Cu-Cu collisions at 62.4 and 200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider. The elliptic flow in Cu-Cu collisions is found to be significant even for the most central events. For comparison with the Au-Au results, it is found that the detailed way in which the collision geometry (eccentricity) is estimated is of critical importance when scaling out system-size effects. A new form of eccentricity, called the participant eccentricity, is introduced which yields a scaled elliptic flow in the Cu-Cu system that has the same relative magnitude and qualitative features as that in the Au-Au system.

The breakout reaction ${}^{15}\mathrm{O}(\alpha ,\gamma ){}^{19}\mathrm{Ne}$, which regulates the flow between the hot CNO cycle and the $rp$ process, is critical for the explanation of the burst amplitude and periodicity of x-ray bursters. We report on the first successful measurement of the critical $\alpha$-decay branching ratios of relevant states in ${}^{19}\mathrm{Ne}$ populated via ${}^{19}\mathrm{F}({}^3\mathrm{He},t){}^{19}\mathrm{Ne}$. Based on the experimental results and our previous lifetime measurements of these states, we derive the first experimental rate of ${}^{15}\mathrm{O}(\alpha ,\gamma ){}^{19}\mathrm{Ne}$. The impact of our experimental results on the burst pattern and periodicity for a range of accretion rates is analyzed.

The differential and total cross sections for the $dp\to {}^3\mathrm{He}\eta$ reaction have been measured in a high precision high statistics COSY-ANKE experiment near threshold using a continuous beam energy ramp up to an excess energy $Q$ of 11.3 MeV with essentially 100% acceptance. The kinematics allowed the mean value of $Q$ to be determined to about 9 keV. Evidence is found for the effects of higher partial waves for $Q\gtrsim 4\mathrm{MeV}$. The very rapid rise of the total cross section to its maximum value within 0.5 MeV of threshold implies a very large $\eta {}^3\mathrm{He}$ scattering length and hence the presence of a quasibound state extremely close to threshold.

We show that partial dynamical symmetries can occur at critical points of quantum phase transitions, in which case underlying competing symmetries are conserved exactly by a subset of states, and mix strongly in other states. Several types of partial dynamical symmetries are demonstrated with the example of critical-point Hamiltonians for first- and second-order transitions in the framework of the interacting boson model, whose dynamical symmetries correspond to different shape phases in nuclei.

We provide integrated cross sections for quasielastic charged-current neutrino-nucleus scattering. Results evaluated using the phenomenological scaling function extracted from the analysis of experimental ($e$, $e^{\prime }$) data are compared with those obtained within the framework of the relativistic impulse approximation. We show that very reasonable agreement is reached when a description of final-state interactions based on the relativistic mean field is included. This is consistent with previous studies of differential cross sections which are in accord with the universality property of the superscaling function.

We examine manifestations of neutron electromagnetic polarizabilities in coherent Compton scattering from the helium-3 nucleus. We calculate $\gamma {}^3\mathrm{He}$ elastic scattering observables using chiral perturbation theory to next-to-leading order [$\mathcal{O}(e^{2}Q)$]. We find that the unpolarized differential cross section can be used to measure neutron electric and magnetic polarizabilities, while two double-polarization observables are sensitive to different linear combinations of the four neutron spin polarizabilities.

A measurement of neutrinoless double beta decay in one isotope does not allow us to determine the underlying physics mechanism. We discuss the discrimination of mechanisms for neutrinoless double beta decay by comparing ratios of half-life measurements for different isotopes. Six prominent examples for specific new physics contributions to neutrinoless double beta decay are analyzed. We find that the change in corresponding ratios of half lives varies from 60% for supersymmetric models up to a factor of 5–20 for extra-dimensional and left-right-symmetric mechanisms.

The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) has measured $J/\psi$ production for rapidities $-2.2<y<2.2$ in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. The $J/\psi$ invariant yield and nuclear modification factor $R_{AA}$ as a function of centrality, transverse momentum, and rapidity are reported. A suppression of $J/\psi$ relative to binary collision scaling of proton-proton reaction yields is observed. Models which describe the lower energy $J/\psi$ data at the CERN Super Proton Synchrotron invoking only $J/\psi$ destruction based on the local medium density predict a significantly larger suppression at RHIC and more suppression at midrapidity than at forward rapidity. Both trends are contradicted by our data.

We present azimuthal angle correlations of intermediate transverse momentum () hadrons from dijets in and collisions at and 200 GeV. The away-side dijet induced azimuthal correlation is broadened, non-Gaussian, and peaked away from in central and semicentral collisions in all the systems. The broadening and peak location are found to depend upon the number of participants in the collision, but not on the collision energy or beam nuclei. These results are consistent with sound or shock wave models, but pose challenges to Cherenkov gluon radiation models.

Dihadron spectra in high-energy heavy-ion collisions are studied within the next-to-leading order perturbative QCD parton model with modified jet fragmentation functions due to jet quenching. High-$p_T$ back-to-back dihadrons are found to originate mainly from jet pairs produced close and tangential to the surface of the dense matter. However, a substantial fraction also comes from jets produced at the center with finite energy loss. Consequently, high-$p_T$ dihadron spectra are found to be more sensitive to the initial gluon density than the single hadron spectra that are more dominated by surface emission. A simultaneous ${\chi }^2$ fit to both the single and dihadron spectra can be achieved within a range of the energy loss parameter ${ϵ}_0=1.6–2.1\mathrm{GeV}/\mathrm{fm}$. Because of the flattening of the initial jet production spectra at $\sqrt{s}=5.5\mathrm{TeV}$, high $p_T$ dihadrons are found to be more robust as probes of the dense medium.