We present an extensive study of nuclear matrix elements (NME) for the neutrinoless double-beta decay of the nuclei ${}^{48}\mathrm{Ca}$, ${}^{76}\mathrm{Ge}$, ${}^{82}\mathrm{Se}$, ${}^{96}\mathrm{Zr}$, ${}^{100}\mathrm{Mo}$, ${}^{116}\mathrm{Cd}$, ${}^{124}\mathrm{Sn}$, ${}^{128}\mathrm{Te}$, ${}^{130}\mathrm{Te}$, ${}^{136}\mathrm{Xe}$, and ${}^{150}\mathrm{Nd}$ based on state-of-the-art energy density functional methods using the Gogny D1S functional. Beyond-mean-field effects are included within the generating coordinate method with particle number and angular momentum projection for both initial and final ground states. We obtain a rather constant value for the NMEs around 4.7 with the exception of ${}^{48}\mathrm{Ca}$ and ${}^{150}\mathrm{Nd}$, where smaller values are found. We analyze the role of deformation and pairing in the evaluation of the NME and present detailed results for the decay of ${}^{150}\mathrm{Nd}$.

A very exotic process of $\beta$-delayed fission of ${}^{180}\mathrm{Tl}$ is studied in detail by using resonant laser ionization with subsequent mass separation at ISOLDE (CERN). In contrast to common expectations, the fission-fragment mass distribution of the post-$\beta$-decay daughter nucleus ${}^{180}\mathrm{Hg}$ ($N/Z=1.25$) is asymmetric. This asymmetry is more surprising since a mass-symmetric split of this extremely neutron-deficient nucleus would lead to two ${}^{90}\mathrm{Zr}$ fragments, with magic $N=50$ and semimagic $Z=40$. This is a new type of asymmetric fission, not caused by large shell effects related to fragment magic proton and neutron numbers, as observed in the actinide region. The newly measured branching ratio for $\beta$-delayed fission of ${}^{180}\mathrm{Tl}$ is $3.6(7)\times {10}^{-3}\%$, approximately 2 orders of magnitude larger than in an earlier study.

The first measurement of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{NN}}=2.76\mathrm{TeV}$ is presented. For an event sample corresponding to the most central 5% of the hadronic cross section, the pseudorapidity density of primary charged particles at midrapidity is $1584\pm 4(\mathrm{stat})\pm 76(\mathrm{syst})$, which corresponds to $8.3\pm 0.4(\mathrm{syst})$ per participating nucleon pair. This represents an increase of about a factor 1.9 relative to $pp$ collisions at similar collision energies, and about a factor 2.2 to central Au-Au collisions at $\sqrt{s_{NN}}=0.2\mathrm{TeV}$. This measurement provides the first experimental constraint for models of nucleus-nucleus collisions at LHC energies.

We report the first measurement of charged particle elliptic flow in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$ with the ALICE detector at the CERN Large Hadron Collider. The measurement is performed in the central pseudorapidity region ($|\eta |<0.8$) and transverse momentum range $0.2<p_t<5.0\mathrm{GeV}/c$. The elliptic flow signal $v_2$, measured using the 4-particle correlation method, averaged over transverse momentum and pseudorapidity is $0.087\pm 0.002(\mathrm{stat})\pm 0.003(\mathrm{syst})$ in the 40%–50% centrality class. The differential elliptic flow $v_2(p_t)$ reaches a maximum of 0.2 near $p_t=3\mathrm{GeV}/c$. Compared to RHIC Au-Au collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$, the elliptic flow increases by about 30%. Some hydrodynamic model predictions which include viscous corrections are in agreement with the observed increase.

By using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally segmented electromagnetic and hadronic calorimeters. The transverse energies of dijets in opposite hemispheres are observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.

The “island of inversion” nucleus ${}^{32}\mathrm{Mg}$ has been studied by a ($t$, $p$) two neutron transfer reaction in inverse kinematics at REX-ISOLDE. The shape coexistent excited $0^{+}$ state in ${}^{32}\mathrm{Mg}$ has been identified by the characteristic angular distribution of the protons of the $\Delta L=0$ transfer. The excitation energy of 1058 keV is much lower than predicted by any theoretical model. The low $\gamma$-ray intensity observed for the decay of this $0^{+}$ state indicates a lifetime of more than 10 ns. Deduced spectroscopic amplitudes are compared with occupation numbers from shell-model calculations.

For nuclei near a maximum of the neutron strength function, the secular dependence on energy $E$ of $s$-wave partial neutron widths differs from the canonical form $\sqrt{E}$. We derive the universal form of that dependence and show that it is expected to significantly influence the analysis of neutron resonance data.

We report on a study of the $nd$ and $n{}^3\mathrm{He}$ radiative captures at thermal neutron energies, using wave functions obtained from either chiral or conventional two- and three-nucleon realistic potentials with the hyperspherical-harmonics method, and electromagnetic currents derived in chiral effective field theory up to one loop. The predicted $nd$ and $n{}^3\mathrm{He}$ cross sections are in good agreement with data, but exhibit a significant dependence on the input Hamiltonian. A comparison is also made between these and new results for the $nd$ and $n{}^3\mathrm{He}$ cross sections obtained in the conventional framework for both potentials and currents.

The double-peak structure observed in soft-hard hadron correlations is commonly interpreted as a signature for a Mach cone generated by a supersonic jet interacting with the hot and dense medium created in ultrarelativistic heavy-ion collisions. We show that it can also arise due to averaging over many jet events in a transversally expanding background. We find that the jet-induced away-side yield does not depend on the details of the energy-momentum deposition in the plasma, the jet velocity, or the system size. Our claim can be experimentally tested by comparing soft-hard correlations induced by heavy-flavor jets with those generated by light-flavor jets.

We have measured the ${}^3\mathrm{He}(e,e^{\prime }pp)n$ reaction at an incident energy of 4.7 GeV over a wide kinematic range. We identified spectator correlated $pp$ and $pn$ nucleon pairs by using kinematic cuts and measured their relative and total momentum distributions. This is the first measurement of the ratio of $pp$ to $pn$ pairs as a function of pair total momentum $p_{\mathrm{tot}}$. For pair relative momenta between 0.3 and $0.5\mathrm{GeV}/c$, the ratio is very small at low $p_{\mathrm{tot}}$ and rises to approximately 0.5 at large $p_{\mathrm{tot}}$. This shows the dominance of tensor over central correlations at this relative momentum.

The pygmy dipole resonance has been studied in the proton-magic nucleus ${}^{124}\mathrm{Sn}$ with the ($\alpha$, ${\alpha }^{\prime }\gamma$) coincidence method at $E_{\alpha }=136\mathrm{MeV}$. The comparison with results of photon-scattering experiments reveals a splitting into two components with different structure: one group of states which is excited in ($\alpha$, ${\alpha }^{\prime }\gamma$) as well as in ($\gamma$, ${\gamma }^{\prime }$) reactions and a group of states at higher energies which is only excited in ($\gamma$, ${\gamma }^{\prime }$) reactions. Calculations with the self-consistent relativistic quasiparticle time-blocking approximation and the quasiparticle phonon model are in qualitative agreement with the experimental results and predict a low-lying isoscalar component dominated by neutron-skin oscillations and a higher-lying more isovector component on the tail of the giant dipole resonance.

Rotational motion of heated ${}^{72}\mathrm{Ge}$ is studied within the microscopic shell-model Monte Carlo approach. We investigate the angular momentum alignment and nuclear pairing correlations associated with $J^{\pi }$ Cooper pairs as a function of the rotational frequency and temperature. The reentrance of pairing correlations with temperature is predicted at high rotational frequencies. It manifests itself through the anomalous behavior of specific heat and level density.

Density functionals for nuclei usually include an effective 3-body interaction that depends on a fractional power of the density. Using insights from the many-body theory of the low-density two-component Fermi gas, we consider a new, nonlocal, form for the energy functional that is consistent with the Fock-space representation of interaction operators. In particular, there is a unique spatially nonlocal generalization of the contact form of the interaction that preserves the ${\rho }^{7/3}$ density dependence required by the many-body theory. We calculate the ground-state energies for particles in a harmonic trap by using the nonlocal induced 3-body interaction and compare them to numerically accurate Green’s function Monte Carlo calculations. Using no free parameters, we find that a nonlocality in the space domain provides a better description of the weak-coupling regime than the local-density approximation.

We present new data on electron scattering from a range of nuclei taken in Hall C at Jefferson Lab. For heavy nuclei, we observe a rapid falloff in the cross section for $x>1$, which is sensitive to short-range contributions to the nuclear wave function, and in deep inelastic scattering corresponds to probing extremely high momentum quarks. This result agrees with higher energy muon scattering measurements, but is in sharp contrast to neutrino scattering measurements which suggested a dramatic enhancement in the distribution of the “superfast” quarks probed at $x>1$. The falloff at $x>1$ is noticeably stronger in ${}^2\mathrm{H}$ and ${}^3\mathrm{He}$, but nearly identical for all heavier nuclei.

The contribution of $B$ meson decays to nonphotonic electrons, which are mainly produced by the semileptonic decays of heavy-flavor mesons, in $p+p$ collisions at $\sqrt{s}=200\mathrm{GeV}$ has been measured using azimuthal correlations between nonphotonic electrons and hadrons. The extracted $B$ decay contribution is approximately 50% at a transverse momentum of $p_T\ge 5\mathrm{GeV}/c$. These measurements constrain the nuclear modification factor for electrons from $B$ and $D$ meson decays. The result indicates that $B$ meson production in heavy ion collisions is also suppressed at high $p_T$.

A microscopic calculation of reaction cross sections for nucleon-nucleus scattering was performed by coupling the elastic channel to all particle-hole excitations in the target and one-nucleon pickup channels. The particle-hole states may be regarded as doorway states through which the flux flows to more complicated configurations, and subsequently to long-lived compound nucleus resonances. Target excitations for ${}^{40,48}\mathrm{C}\mathrm{a}$, ${}^{58}\mathrm{N}\mathrm{i}$, ${}^{90}\mathrm{Z}\mathrm{r}$, and ${}^{144}\mathrm{S}\mathrm{m}$ were described in a random-phase framework using a Skyrme functional. Reaction cross sections obtained agreed very well with experimental data and predictions of a fitted optical potential. Couplings between inelastic states were found to be negligible, while the pickup channels contribute significantly. For the first time observed absorptions are completely accounted for by explicit channel coupling, for incident energies between 10 and 40 MeV.

The $\beta$ feeding probability of ${}^{102,104,105,106,107}\mathrm{Tc}$, ${}^{105}\mathrm{Mo}$, and ${}^{101}\mathrm{Nb}$ nuclei, which are important contributors to the decay heat in nuclear reactors, has been measured using the total absorption technique. We have coupled for the first time a total absorption spectrometer to a Penning trap in order to obtain sources of very high isobaric purity. Our results solve a significant part of a long-standing discrepancy in the $\gamma$ component of the decay heat for ${}^{239}\mathrm{Pu}$ in the 4–3000 s range.

A particle-number projection technique is used to calculate transfer probabilities in the ${}^{16}\mathrm{O}+{}^{208}\mathrm{Pb}$ reaction below the fusion barrier. The time evolution of the many-body wave function is obtained with the time-dependent Hartree-Fock (TDHF) mean-field theory. The agreement with experimental data for the sum of the proton-transfer channels is good, considering that TDHF has no parameter adjusted on the reaction mechanism. Some perspectives for extensions beyond TDHF to include cluster transfers are discussed.

The new, neutron-deficient, superheavy element isotope ${}^{285}114$ was produced in ${}^{48}\mathrm{Ca}$ irradiations of ${}^{242}\mathrm{Pu}$ targets at a center-of-target beam energy of 256 MeV ($E^{*}=50\mathrm{MeV}$). The $\alpha$ decay of ${}^{285}114$ was followed by the sequential $\alpha$ decay of four daughter nuclides, ${}^{281}\mathrm{Cn}$, ${}^{277}\mathrm{Ds}$, ${}^{273}\mathrm{Hs}$, and ${}^{269}\mathrm{Sg}$. ${}^{265}\mathrm{Rf}$ was observed to decay by spontaneous fission. The measured $\alpha$-decay $Q$ values were compared with those from a macroscopic-microscopic nuclear mass model to give insight into superheavy element shell effects. The ${}^{242}\mathrm{Pu}({}^{48}\mathrm{Ca},5n){}^{285}114$ cross section was ${0.6}_{-0.5}^{+0.9}\mathrm{pb}$.

PHENIX Collaboration and STAR Collaboration data on the intercept parameter of the two-pion Bose-Einstein correlation functions in $\sqrt{s_{NN}}=200\mathrm{GeV}$ $\mathrm{Au}+\mathrm{Au}$ collisions are analyzed in terms of different models of hadronic multiplicities. To describe this combined PHENIX and STAR data set, an in-medium ${\eta }^{\prime }$ mass reduction of at least 200 MeV is needed, at the 99.9% confidence level in the considered model class. Such a significant ${\eta }^{\prime }$ mass modification may indicate the restoration of the $U_A(1)$ symmetry in a hot and dense hadronic matter and the return of the 9th “prodigal” Goldstone boson.