A rotational band has been unambiguously observed in an odd-proton transfermium nucleus for the first time. An in-beam $\gamma$-ray spectroscopic study of ${}_{101}{}^{251}\mathrm{Md}$ has been performed using the $\gamma$-ray array JUROGAM combined with the gas-filled separator RITU and the focal plane device GREAT. The experimental results, compared to Hartree-Fock-Bogolyubov calculations, lead to the interpretation that the rotational band is built on the $[521]1/2^{-}$ Nilsson state.

Two-nucleon momentum distributions are calculated for the ground states of nuclei with mass number $A\le 8$, using variational Monte Carlo wave functions derived from a realistic Hamiltonian with two- and three-nucleon potentials. The momentum distribution of $np$ pairs is found to be much larger than that of $pp$ pairs for values of the relative momentum in the range $(300–600)\mathrm{MeV}/c$ and vanishing total momentum. This order of magnitude difference is seen in all nuclei considered and has a universal character originating from the tensor components present in any realistic nucleon-nucleon potential. The correlations induced by the tensor force strongly influence the structure of $np$ pairs, which are predominantly in deuteronlike states, while they are ineffective for $pp$ pairs, which are mostly in ${}^{1}S_0$ states. These features should be easily observable in two-nucleon knockout processes, such as $A(e,e^{\prime }np)$ and $A(e,e^{\prime }pp)$.

Calculations of nuclear masses, using nuclear density functional theory, are presented for even-even nuclei spanning the nuclear chart. The resulting binding energy differences can be interpreted in terms of valence proton-neutron interactions. These are compared globally, regionally, and locally with empirical values. Overall, excellent agreement is obtained. Discrepancies highlight neglected degrees of freedom and can point to improved density functionals.

Emission source functions are extracted from correlation functions constructed from charged pions produced at midrapidity in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. The source parameters extracted from these functions at low $k_T$ give first indications of a long tail for the pion emission source. The source extension cannot be explained solely by simple kinematic considerations. The possible role of a halo of secondary pions from resonance emissions is explored.

We report on the first low-energy Coulomb excitation measurements with radioactive $I^{\pi }=6^{-}$ beams of odd-odd nuclei ${}^{68,70}\mathrm{Cu}$. The beams were produced at ISOLDE, CERN and were post-accelerated by REX-ISOLDE to $2.83\mathrm{MeV}/\mathrm{\text{nucleon}}$. $\gamma$ rays were detected with the MINIBALL spectrometer. The $6^{-}$ beam was used to study the multiplet of states ($3^{-}$, $4^{-}$, $5^{-}$, $6^{-}$) arising from the $\pi 2p_{3/2}\nu 1g_{9/2}$ configuration. The $4^{-}$ state of the multiplet was populated via Coulomb excitation and the $B(E2;6^{-}\to 4^{-})$ value was determined in both nuclei. The results obtained illustrate the fragile stability of the $Z=28$ shell and $N=40$ subshell closures. A comparison with large-scale shell-model calculations using the ${}^{56}\mathrm{Ni}$ core shows the importance of the proton excitations across the $Z=28$ shell gap to the understanding of the nuclear structure in the neutron-rich nuclei with $N\approx 40$.

The fusion reactions ${}^{12}\mathrm{C}({}^{12}\mathrm{C},\alpha ){}^{20}\mathrm{Ne}$ and ${}^{12}\mathrm{C}({}^{12}\mathrm{C},p){}^{23}\mathrm{Na}$ have been studied from $E=2.10$ to 4.75 MeV by $\gamma$-ray spectroscopy using a C target with ultralow hydrogen contamination. The deduced astrophysical $S(E{)}^{*}$ factor exhibits new resonances at $E\le 3.0\mathrm{MeV}$, in particular, a strong resonance at $E=2.14\mathrm{MeV}$, which lies at the high-energy tail of the Gamow peak. The resonance increases the present nonresonant reaction rate of the $\alpha$ channel by a factor of 5 near $T=8\times {10}^8\mathrm{K}$. Because of the resonance structure, extrapolation to the Gamow energy $E_G=1.5\mathrm{MeV}$ is quite uncertain. An experimental approach based on an underground accelerator placed in a salt mine in combination with a high efficiency detection setup could provide data over the full $E_G$ energy range.

The shape of exotic even-mass ${}^{182–190}\mathrm{Pb}$ isotopes was probed by measurement of optical isotope shifts providing mean square charge radii ($\delta ⟨r^2⟩$). The experiment was carried out at the isolde (cern) on-line mass separator, using in-source laser spectroscopy. Small deviations from the spherical droplet model are observed, but when compared to model calculations, those are explained by high sensitivity of $\delta ⟨r^2⟩$ to beyond mean-field correlations and small admixtures of intruder configurations in the ground state. The data support the predominantly spherical shape of the ground state of the proton-magic $Z=82$ lead isotopes near neutron midshell ($N=104$).

We compare coupled-cluster (CC) and configuration-interaction (CI) results for ${}^{56}\mathrm{Ni}$ obtained in the $pf$-shell basis, focusing on practical CC approximations that can be applied to systems with dozens or hundreds of correlated fermions. The weight of the reference state and the strength of correlation effects are controlled by the gap between the $f_{7/2}$ orbit and the $f_{5/2}$, $p_{3/2}$, $p_{1/2}$ orbits. Independent of the gap, the CC method with 1p-1h and 2p-2h clusters and a noniterative treatment of 3p-3h clusters is as accurate as the more demanding CI approach truncated at the 4p-4h level.

We present an accurate numerical study of the equation of state of nuclear matter based on realistic nucleon-nucleon interactions by means of auxiliary field diffusion Monte Carlo (AFDMC) calculations. The AFDMC method samples the spin and isospin degrees of freedom allowing for quantum simulations of large nucleonic systems and represents an important step forward towards a quantitative understanding of problems in nuclear structure and astrophysics.

Neutron single particle energies have been measured in ${}^{23}\mathrm{O}$ using the ${}^{22}\mathrm{O}(d,p){}^{23}\mathrm{O}^{*}\to {}^{22}\mathrm{O}+n$ process. The energies of the resonant states have been deduced to be 4.00(2) MeV and 5.30(4) MeV. The first excited state can be assigned to the $\nu d_{3/2}$ single particle state from a comparison with shell model calculations. The measured 4.0 MeV energy difference between the $\nu s_{1/2}$ and $\nu d_{3/2}$ states gives the size of the $N=16$ shell gap which is in agreement with the recent USD05 (“universal” sd from 2005) shell model calculation, and is large enough to explain the unbound nature of the oxygen isotopes heavier than $A=24$. The resonance detected at 5.3 MeV can be assigned to a state out of the $sd$ shell model space. Its energy corresponds to a $\sim 1.3\mathrm{MeV}$ sized $N=20$ shell gap, therefore, the $N=20$ shell closure disappears at $Z=8$ in agreement with Monte Carlo shell model calculations using SDPF-M interaction.

A study of the nucleus ${}^{106}\mathrm{Ag}$ has revealed the presence of two strongly coupled negative-parity rotational bands up to the ${19}^{-}$ and ${20}^{-}$ states, respectively, which cross each other at spin $I\sim 14$. The data suggest that near the crossover point the bands correspond to different shapes, which is different to the behavior expected from a pair of chiral bands. Inspection of the properties of these bands indicates a triaxial and a planar nature of rotation for the two structures. Possible causes for this may be understood in terms of a shape transformation resulting from the large degree of $\gamma$ softness of ${}^{106}\mathrm{Ag}$. These data, along with the systematics of the odd-odd structures in the mass 100 region, suggest that $\gamma$ softness has marked implications for the phenomenon of nuclear chirality.

The shear viscosity to entropy ratio ($\eta /s$) is estimated for the hot and dense QCD matter created in $\mathrm{Au}+\mathrm{Au}$ collisions at BNL Relativistic Heavy Ion Collider ($\sqrt{s_{NN}}=200\mathrm{GeV}$). A very low value is found; $\eta /s\sim 0.1$, which is close to the conjectured lower bound ($1/4\pi$). It is argued that such a low value is indicative of thermodynamic trajectories for the decaying matter which lie close to the QCD critical end point.

The Gamow-Teller strength distributions below the particle threshold in ${}^{138}\mathrm{La}$ and ${}^{180}\mathrm{Ta}$, deduced from high-resolution measurements of the (${}^3\mathrm{He},t$) reaction at 0°, allow us to evaluate the role of charged-current reactions for the production of these extremely rare nuclides in neutrino-nucleosynthesis models. The analysis suggests that essentially all ${}^{138}\mathrm{La}$ in the Universe can be made that way. Neutrino nucleosynthesis also contributes significantly to the abundance of ${}^{180}\mathrm{Ta}$ but the magnitude depends on the unknown branching ratio for population of the long-lived isomer.

We report on the first genuinely three-body $\overline{K}NN-\pi \Sigma N$ coupled-channel Faddeev calculation in search for quasibound states in the $K^{-}pp$ system. The main absorptivity in the $K^{-}p$ subsystem is accounted for by fitting to $K^{-}p$ data near threshold. Our calculation yields one such quasibound state, with $I=1/2$, $J^{\pi }=0^{-}$, bound in the range $B\sim 55–70\mathrm{MeV}$, with a width of $\Gamma \sim 90–110\mathrm{MeV}$. These results differ substantially from previous estimates, and are at odds with the $K^{-}pp\to \Lambda p$ signal observed by the FINUDA collaboration.

Using a method whereby molecular and atomic ions are independently selected, an isobarically pure beam of ${}^{70}\mathrm{Se}$ ions was postaccelerated to an energy of 206 MeV using REX-ISOLDE. Coulomb-excitation yields for states in the beam and target nuclei were deduced by recording deexcitation $\gamma$ rays in the highly segmented MINIBALL $\gamma$-ray spectrometer in coincidence with scattered particles in a silicon detector. At these energies, the Coulomb-excitation yield for the first $2^{+}$ state is expected to be strongly sensitive to the sign of the spectroscopic quadrupole moment through the nuclear reorientation effect. Experimental evidence is presented here for a prolate shape for the first $2^{+}$ state in ${}^{70}\mathrm{Se}$, reopening the question over whether there are, as reported earlier, deformed oblate shapes near to the ground state in the light selenium isotopes.

We present the scaling properties of $\Lambda$, $\Xi$, and $\Omega$ in midrapidity $\mathrm{Au}+\mathrm{Au}$ collisions at the Brookhaven National Laboratory Relativistic Heavy Ion Collider at $\sqrt{s_{NN}}=200\mathrm{GeV}$. The yield of multistrange baryons per participant nucleon increases from peripheral to central collisions more rapidly than that of $\Lambda$, indicating an increase of the strange-quark density of the matter produced. The strange phase-space occupancy factor ${\gamma }_s$ approaches unity for the most central collisions. Moreover, the nuclear modification factors of $p$, $\Lambda$, and $\Xi$ are consistent with each other for $2<p_T<5\mathrm{GeV}/c$ in agreement with a scenario of hadron formation from constituent quark degrees of freedom.

The invariant-mass spectrum of $e^{+}{e}^{-}$ pairs produced in ${}^{12}\mathrm{C}+{}^{12}\mathrm{C}$ collisions at an incident energy of 2 GeV per nucleon has been measured for the first time. The measured pair production probabilities span over 5 orders of magnitude from the ${\pi }^0$-Dalitz to the $\rho /\omega$ invariant-mass region. Dalitz decays of ${\pi }^0$ and $\eta$ account for all the yield up to $0.15\mathrm{GeV}/c^2$, but for only about 50% above this mass. A comparison with model calculations shows that the excess pair yield is likely due to baryon-resonance and vector-meson decays. Transport calculations based on vacuum spectral functions fail, however, to describe the entire mass region.

We report the first precision measurement of the proton electric to magnetic form factor ratio from spin-dependent elastic scattering of longitudinally polarized electrons from a polarized hydrogen internal gas target. The measurement was performed at the MIT-Bates South Hall Ring over a range of four-momentum transfer squared $Q^2$ from 0.15 to $0.65(\mathrm{GeV}/c{)}^2$. Significantly improved results on the proton electric and magnetic form factors are obtained in combination with existing cross-section data on elastic electron-proton scattering in the same $Q^2$ region.

We investigate phase transitions in boson-fermion systems. We propose an analytically solvable model [$E(5/12)$] to describe odd nuclei at the critical point in the transition from the spherical to $\gamma$-unstable behavior. In the model, a boson core described within the Bohr Hamiltonian interacts with an unpaired particle assumed to be moving in the three single-particle orbitals $j=1/2$, $3/2$, $5/2$. Energy spectra and electromagnetic transitions at the critical point compare well with the results obtained within the interacting boson-fermion model, with a boson-fermion Hamiltonian that describes the same physical situation.

Invariant mass spectra of $e^{+}{e}^{-}$ pairs have been measured in 12 GeV $p+A$ reactions to detect possible in-medium modification of vector mesons. Copper and carbon targets are used to study the nuclear-size dependence of $e^{+}{e}^{-}$ invariant mass distributions. A significant excess on the low-mass side of the $\varphi$ meson peak is observed in the low $\beta \gamma (=\beta /\sqrt{1-{\beta }^2})$ region of $\varphi$ mesons ($\beta \gamma <1.25$) with copper targets. However, in the high $\beta \gamma$ region ($\beta \gamma >1.25$), spectral shapes of $\varphi$ mesons are well described by the Breit-Wigner shape when experimental effects are considered. Thus, in addition to our earlier publications on $\rho /\omega$ modification, this study has experimentally verified vector meson mass modification at normal nuclear density.