Rotational bands in ${}^{158}$Er at ultrahigh spin have been studied in the framework of relativistic and nonrelativistic nuclear density-functional theories. Consistent results are obtained across the theoretical models used but some puzzles remain when confronted with experiment. Namely, the many-body configurations which provide good description of experimental transition quadrupole moments and dynamic moments of inertia require substantial increase of the spins of observed bands as compared with experimental estimates, which are still subject to large uncertainties. If, however, the theoretical spin assignments turned out to be correct, experimental band 1 in ${}^{158}$Er would be the highest spin structure ever observed.

Background: Gamow-Teller (GT) transition strength distributions in stable and unstable $pf$-shell isotopes are key inputs for estimating electron-capture rates important for stellar evolution. Charge-exchange experiments at intermediate beam energies have long been used to test theoretical predictions for GT strengths, but previous experiments were largely restricted to stable nuclei. Since a large fraction of the nuclei relevant for astrophysical applications (including key nuclei such as ${}^{56}$Ni) are unstable, new methods are needed to perform charge-exchange experiments in inverse kinematics with unstable isotopes.

Purpose: The ${}^{56}$Ni($p,n$) and ${}^{55}$Co($p,n$) reactions were measured in inverse kinematics in order to extract GT strengths for transitions to ${}^{56}$Cu and ${}^{55}$Ni, respectively. The extracted strength distributions were compared with shell-model predictions in the $pf$ shell using the KB3G and GXPF1J interactions. By invoking isospin symmetry, these strength distributions are relevant for electron captures on the ground states of ${}^{56}$Ni and ${}^{55}$Ni to final states in ${}^{56}$Co and ${}^{55}$Co, respectively.

Method: Differential cross sections and excitation energy spectra for the ${}^{56}$Ni($p,n$) and ${}^{55}$Co($p,n$) reactions were determined by measuring neutrons recoiling from a liquid hydrogen target into the Low Energy Neutron Detector Array. GT contributions to the spectra were extracted by using a multipole decomposition analysis and were converted to strengths by employing the proportionality between GT strength and differential cross section at zero linear momentum transfer.

Results: GT strengths from ${}^{56}$Ni and ${}^{55}$Co were extracted up to excitation energies of 8 and 15 MeV, respectively. Shell-model calculations performed in the $pf$ shell with the GXPF1J interaction reproduced the experimental GT strength distributions better than calculations with the KB3G interaction.

Conclusions: A new technique for measuring ($p,n$) charge-exchange reactions on unstable nuclei was successfully developed. It can be used to study the isovector response of unstable nuclei in any mass region and for excitation energies beyond the particle decay threshold. In the first experiment, ${}^{56}$Ni($p,n$) and ${}^{55}$Co($p,n$) reactions were studied and GT transition strengths were extracted for the purpose of testing shell-model calculations used to estimate electron-capture rates in simulations of late stellar evolution. The calculation using the GXPF1J interaction was found to best reproduce the experimental strength distribution.

Background: Time-reversal-invariance violation, or equivalently $CP$ violation, may explain the observed cosmological baryon asymmetry as well as indicate physics beyond the Standard Model. In the decay of polarized neutrons, the triple correlation $D\langle {\vec{J}}_n\rangle /J_n·({\vec{\beta }}_e\times {\widehat{p}}_{\nu })$ is a parity-even, time-reversal-odd observable that is uniquely sensitive to the relative phase of the axial-vector amplitude with respect to the vector amplitude. The triple correlation is also sensitive to possible contributions from scalar and tensor amplitudes. Final-state effects contribute to $D$ at the level of 10${}^{-5}$ and can be calculated with a precision of 1$\%$ or better.

Purpose: We have improved the sensitivity to $T$-odd, $P$-even interactions in nuclear $\beta$ decay.

Methods: We measured proton-electron coincidences from decays of longitudinally polarized neutrons with a highly symmetric detector array designed to cancel the time-reversal-even, parity-odd Standard-Model contributions to polarized neutron decay. Over 300 million proton-electron coincidence events were used to extract $D$ and study systematic effects in a blind analysis.

Results: We find $D=[-0.94\pm 1.89\left(\mathrm{stat}\right)\pm 0.97\left(\mathrm{sys}\right)]\times {10}^{-4}$. This differs from the result of our recent paper [Phys. Rev. Lett. 107, 102301 (2011)] due to refinement of corrections for background and backscattering.

Conclusions: This is the most sensitive measurement of $D$ in nuclear $\beta$ decay. Our result can be interpreted as a measurement of the phase of the ratio of the axial-vector and vector coupling constants ($C_A/C_V=\left|\lambda \right|e^{i{\phi }_{AV}}$) with ${\phi }_{AV}=180.{012}^{\circ }\pm 0.{028}^{\circ }$ (68$\%$ confidence level). This result can also be used to constrain time-reversal-violating scalar and tensor interactions that arise in certain extensions to the Standard Model such as leptoquarks.

Background: Neutrino-nucleus quasi-elastic scattering is crucial to interpret the neutrino oscillation results in long baseline neutrino experiments. There are rather large uncertainties in the cross section, due to insufficient knowledge on the role of two-body weak currents.

Purpose: Determine the role of two-body weak currents in neutrino-deuteron quasi-elastic scattering up to GeV energies.

Methods: Calculate cross sections for inclusive neutrino scattering off deuteron induced by neutral and charge-changing weak currents, from threshold up to GeV energies, using the Argonne $v_{18}$ potential and consistent nuclear electroweak currents with one- and two-body terms.

Results: Two-body contributions are found to be small, and increase the cross sections obtained with one-body currents by less than 10$\%$ over the whole range of energies. Total cross sections obtained by describing the final two-nucleon states with plane waves differ negligibly, for neutrino energies $\gtrsim$ MeV, from those in which interaction effects in these states are fully accounted for. The sensitivity of the calculated cross sections to different models for the two-nucleon potential and/or two-body terms in the weak current is found to be weak. Comparing cross sections to those obtained in a naive model in which the deuteron is taken to consist of a free proton and neutron at rest, nuclear structure effects are illustrated to be non-negligible.

Conclusion: Contributions of two-body currents in neutrino-deuteron quasi-elastic scattering up to GeV are found to be smaller than 10$\%$. Finally, it should be stressed that the results reported in this work do not include pion production channels.

Background: Quadrupole moments of excited nuclear states are important observables for geometrically interpreting nuclear structure in terms of deformed shapes, although data are scarce and sometimes ambiguous, in particular, in neutron-rich nuclides.

Purpose: A measurement was performed for determining the spectroscopic quadrupole moment of the $2_1^{+}$ state of ${}^{140}$Ba in order to clarify the character of quadrupole deformation (prolate or oblate) of the state in its yrast sequence of levels.

Method: We have utilized a new combined technique of lifetime measurement at REX-ISOLDE and MINIBALL using the Doppler-shift attenuation method (DSAM) and a reorientation analysis of Coulomb-excitation yields.

Results: On the basis of the new lifetime of $\tau \left(2_1^{+}\right)=10.4_{-0.8}^{+2.2}$ ps the electric quadrupole moment was determined to be $Q\left(2_1^{+}\right)=-0.52\left(34\right)$ $e$b, indicating a predominant prolate deformation.

Conclusions: This finding is in agreement with beyond-mean-field calculations using the Gogny D1S force and with results from the Monte Carlo shell-model approach.

Neutrino-nucleus coherent elastic scattering provides a theoretically appealing way to measure the neutron part of nuclear form factors. Using an expansion of form factors into moments, we show that neutrinos from stopped pions can probe not only the second moment of the form factor (the neutron radius) but also the fourth moment. Using simple Monte Carlo techniques for argon, germanium, and xenon detectors of 3.5 tonnes, 1.5 tonnes, and 300 kg, respectively, we show that the neutron radii can be found with an uncertainty of a few percent when near a neutrino flux of $3\times {10}^7$ neutrinos/(cm${}^2$ s). If the normalization of the neutrino flux is known independently, one can determine the moments accurately enough to discriminate among the predictions of various nuclear energy functionals.

Recent data on the nuclear modification factor $R_{AA}$ of jet fragments in $2.76$ ATeV Pb+Pb collisions at the Large Hadron Collider (LHC) indicate that the jet-medium coupling in a quark-gluon plasma (QGP) is reduced at LHC energies and not compatible with the coupling deduced from data at the Relativistic Hadron Collider (RHIC). We estimate the reduction factor from a combined fit to the available data on $R_{AA}(\sqrt{s},p_T,b)$ and the elliptic flow $v_2(\sqrt{s},p_T,b)$ at $\sqrt{s}=0.2,2.76$ ATeV over a transverse momentum range $p_T\sim 10–100$ GeV and a broad impact parameter, $b$, range. We use a simple analytic “polytrope” model ($dE/dx=-\kappa E^a{x}^z{T}^c$) to investigate the dynamical jet-energy loss model dependence. Varying $a=0–1$ interpolates between weakly coupled and strongly coupled models of jet-energy dependence while $z=0–2$ covers a wide range of possible jet-path dependencies from elastic and radiative to holographic string mechanisms. Our fit to LHC data indicates an approximate 40$\%$ reduction of the coupling $\kappa$ from RHIC to LHC and excludes energy-loss models characterized by a jet-energy exponent with $a>1/3$. In particular, the rapid rise of $R_{AA}$ with $p_T\ge 10$ GeV combined with the slow variation of the asymptotic $v_2\left(p_T\right)$ at the LHC rules out popular exponential geometric optics models ($a=1$). The LHC data are compatible with $0\le a\le 1/3$ pQCD-like energy-loss models where the jet-medium coupling is reduced by approximately 10$\%$ between RHIC and LHC.

Background: Theoretical calculations of the four-body scattering above the four-body breakup threshold are technically very difficult owing to complicated singularities in the momentum space or boundary conditions in the coordinate space.

Purpose: We aim at calculating the neutron-${}^3$H scattering observables above the four-nucleon breakup threshold.

Methods: We employ Alt, Grassberger, and Sandhas (AGS) integral equations for the four-nucleon transition operators and solve them in the momentum-space framework using the complex-energy method. We significantly improve its accuracy and practical applicability by introducing the numerical integration method with the special weights.

Results: Using realistic nuclear interaction models we obtain fully converged results for the neutron-${}^3$H scattering. Elastic differential cross section and neutron analyzing power as well as the total cross section are calculated at 14.1, 18.0, and 22.1 MeV neutron energy.

Conclusions: Realistic four-nucleon scattering calculations above the four-nucleon breakup threshold are feasible. There is quite good agreement between the theoretical predictions and experimental data for the neutron-${}^3$H scattering in the considered energy regime.

We study the influence of a temperature-dependent shear viscosity over entropy density ratio $\eta /s$, different shear relaxation times ${\tau }_{\pi }$, as well as different initial conditions on the transverse momentum spectra of charged hadrons and identified particles. We investigate the azimuthal flow asymmetries as a function of both collision energy and centrality. The elliptic flow coefficient turns out to be dominated by the hadronic viscosity at RHIC energies. Only at higher collision energies the impact of the viscosity in the QGP phase is visible in the flow asymmetries. Nevertheless, the shear viscosity near the QCD transition region has the largest impact on the collective flow of the system. We also find that the centrality dependence of the elliptic flow is sensitive to the temperature dependence of $\eta /s$.

Following neutron knockout from an ${}^{13}$O beam, ${}^{12}$O fragments were created and the three decay products following two-proton decay were detected. A new ground-state mass was determined by the invariant mass method implying a decay kinetic energy of 1.638(24) MeV, and the width was found to be less than 72 keV. The latter is inconsistent with previous measurements with lower experimental resolutions but consistent with theoretical estimates. The isobaric analog of ${}^{12}$O in ${}^{12}$N was produced from proton knockout reactions with the same beam and decayed by two-proton emission to the isobaric analog state in ${}^{10}$B with a decay kinetic energy of 1.165(29) MeV. It represents only the second case of an analog state where two-proton decay is the only isospin- and energy-conserving particle decay mode. With our measurements of the mass excesses of ${}^{12}$O and its analog, the quadratic form of the isobaric multiplet mass equation was found to fit the $A=12$ quintet and any deviations are less than the magnitude found for the $A=8$ quintet and $A=7$ and 9 quartets.

Background: Electron-capture reaction rates on medium-heavy nuclei are an important ingredient for modeling the late evolution of stars that become core-collapse or thermonuclear supernovae. The estimation of these rates requires the knowledge of Gamow-Teller strength distributions in the ${\beta }^{+}$ direction. Astrophysical models rely on electron-capture rate tables largely based on theoretical models, which must be validated and tested against experimental results.

Purpose: This paper presents a systematic evaluation of the ability of theoretical models to reproduce experimental Gamow-Teller transition strength distributions measured via ($n$,$p$)-type charge-exchange reactions at intermediate beam energies. The focus is on transitions from stable nuclei in the $pf$ shell ($45\le A\le 64$). In addition, the impact of deviations between experimental and theoretical Gamow-Teller strength distributions on derived stellar electron-capture rates is investigated.

Method: Data on Gamow-Teller transitions from 13 nuclei in the $pf$ shell measured via charge-exchange reactions and supplemented with results from $\beta$-decay experiments where available, were compiled and compared with strength distributions calculated in shell models (using the GXPF1a and KB3G effective interactions) and quasiparticle random-phase approximation (QRPA) using ground-state deformation parameters and masses from the finite-range droplet model. Electron-capture rates at relevant stellar temperatures and densities were derived for all distributions and compared.

Results: With few exceptions, shell-model calculations in the $pf$ model space with the KB3G and GXPF1a interactions qualitatively reproduce experimental Gamow-Teller strength distributions of 13 stable isotopes with $45\le A\le 64$. Results from QRPA calculations exhibit much larger deviations from the data and overestimate the total experimental Gamow-Teller strengths. For stellar densities in excess of ${10}^7$ g/cm${}^3$, ground-state electron-capture rates derived from the shell-model calculations using the KB3G (GXPF1a) interaction deviate on average less than 47$\%$ (31$\%$) from those derived from experimental data for which the location of daughter states at low excitation energies are well established. For electron-capture rates derived from Gamow-Teller strengths calculated in QRPA, the deviations are much larger, especially at low stellar densities.

Conclusions: Based on the limited set of test cases available for nuclei in the $pf$ shell, shell-models using the GXPF1a and KB3G interactions can be used to estimate electron-capture rates for astrophysical purposes with relatively good accuracy. Measures of the uncertainties in these rates can serve as input for sensitivity studies in stellar evolution models. Ground-state electron-capture rates based on the QRPA formalism discussed in the paper exhibit much larger deviations than those based on the shell-model calculations and should be used with caution, especially at low stellar densities.

Differential measurements of charged particle azimuthal anisotropy are presented for lead-lead collisions at $\sqrt{s_{NN}}=2.76$ TeV with the ATLAS detector at the LHC, based on an integrated luminosity of approximately 8 $\mu {\mathrm{b}}^{-1}$. This anisotropy is characterized via a Fourier expansion of the distribution of charged particles in azimuthal angle relative to the reaction plane, with the coefficients $v_n$ denoting the magnitude of the anisotropy. Significant $v_2$–$v_6$ values are obtained as a function of transverse momentum ($0.5<p_{\mathrm{T}}<20$ GeV), pseudorapidity ($\left|\eta \right|<2.5$), and centrality using an event plane method. The $v_n$ values for $n\ge 3$ are found to vary weakly with both $\eta$ and centrality, and their $p_{\mathrm{T}}$ dependencies are found to follow an approximate scaling relation, $v_n^{1/n}\left(p_{\mathrm{T}}\right)\propto v_2^{1/2}\left(p_{\mathrm{T}}\right)$, except in the top 5$\%$ most central collisions. A Fourier analysis of the charged particle pair distribution in relative azimuthal angle ($\Delta \phi ={\phi }_{\mathrm{a}}-{\phi }_{\mathrm{b}}$) is performed to extract the coefficients $v_{n,n}=\langle \cos n\Delta \phi \rangle$. For pairs of charged particles with a large pseudorapidity gap ($|\Delta \eta ={\eta }_{\mathrm{a}}-{\eta }_{\mathrm{b}}|>2$) and one particle with $p_{\mathrm{T}}<3$ GeV, the $v_{2,2}$–$v_{6,6}$ values are found to factorize as $v_{n,n}(p_{\mathrm{T}}^{\mathrm{a}},p_{\mathrm{T}}^{\mathrm{b}})\approx v_n\left(p_{\mathrm{T}}^{\mathrm{a}}\right)v_n\left(p_{\mathrm{T}}^{\mathrm{b}}\right)$ in central and midcentral events. Such factorization suggests that these values of $v_{2,2}$–$v_{6,6}$ are primarily attributable to the response of the created matter to the fluctuations in the geometry of the initial state. A detailed study shows that the $v_{1,1}(p_{\mathrm{T}}^{\mathrm{a}},p_{\mathrm{T}}^{\mathrm{b}})$ data are consistent with the combined contributions from a rapidity-even $v_1$ and global momentum conservation. A two-component fit is used to extract the $v_1$ contribution. The extracted $v_1$ is observed to cross zero at $p_{\mathrm{T}}\approx 1.0$ GeV, reaches a maximum at 4–5 GeV with a value comparable to that for $v_3$, and decreases at higher $p_{\mathrm{T}}$.

We propose a model of the nucleon in which quark-diquark configurations immersed in a pion cloud are treated in a manner consistent with Poincaré invariance. With suitably chosen parameters, the computations employing this model reproduce the measured electromagnetic form factors and the quark-spin contribution to the total nucleon angular momentum.

The lifetime of the $J^{\pi }=2_1^{+}$ state in ${}^{10}$C was measured using the Doppler shift attenuation method following the inverse kinematics $p{{(}^{10}\text{B},n)}^{10}$C reaction at 95 MeV. The $2_1^{+}$ state, at 3354 keV, has $\tau =219\pm {\left(7\right)}_{\text{stat}}\pm {\left(10\right)}_{\text{sys}}$ fs, corresponding to a $B\left(E2\right)\downarrow$ of 8.8(3) $e^2$ fm${}^4$. This measurement, combined with that recently determined for ${}^{10}$Be [9.2(3) $e^2$ fm${}^4$], provides a unique challenge to ab initio calculations, testing the structure of these states, including the isospin symmetry of the wave functions. Quantum Monte Carlo calculations using realistic two- and three-nucleon Hamiltonians that reproduce the ${}^{10}$Be $B\left(E2\right)$ value generally predict a larger ${}^{10}$C $B\left(E2\right)$ probability but with considerable sensitivity to the admixture of different spatial symmetry components in the wave functions and to the three-nucleon potential used.

Recent studies of the interaction of vector mesons with nuclei make possible and opportune the study of the interaction of the $J/\psi$ with nuclei and the investigation of the origin of the $J/\psi$ suppression in its propagation thorough a nuclear medium. We observe that the transition of $J/\psi N$ to $VN$ with $V$ being a light vector, $\rho ,\omega ,\phi$, together with the inelastic channels, $J/\psi N\to \overline{D}{\Lambda }_c$ and $J/\psi N\to \overline{D}{\Sigma }_c$, leads to a particular shape of the inelastic cross section. Analogously, we consider the mechanisms where the exchanged $D$ collides with a nucleon and gives $\pi {\Lambda }_c$ or $\pi {\Sigma }_c$. The cross section has a peak around $\sqrt{s}=4415$ MeV, where the $J/\psi N$ couples to a resonance predicted recently. We study the transparency ratio for electron-induced $J/\psi$ production in nuclei at about 10 GeV and find that 30–35$\%$ of the $J/\psi$ produced in heavy nuclei are absorbed inside the nucleus. This ratio is in line with depletions of $J/\psi$ through matter observed in other reactions.

The ${}^{12}$C($\alpha ,\gamma$)${}^{16}$O reaction is one of the most important in nuclear astrophysics since it determines the ratio of ${}^{12}$C to ${}^{16}$O during stellar helium burning. Experimental data, however, are still subject to large uncertainties due to the almost vanishing cross section at stellar energies. So far, most measurements have been performed with germanium detectors. To compensate for their low efficiency, the highest beam currents had to be used, resulting in target degradation and beam-induced backgrounds. Instead, the present measurement was performed with high-efficiency detectors and low beam currents, using the Karlsruhe 4$\pi$ BaF${}_2$ detector and the pulsed 3.7-MV Van de Graaff accelerator at Karlsruhe Institute of Technology. The ${}^{12}$C($\alpha ,\gamma$)${}^{16}$O cross sections have been measured at center-of-mass energies $E$ between 1002 and 1510 keV, and the $E1$ and $E2$ components were derived with an accuracy comparable to the previous best data obtained with HPGe detectors.

A ${}^{76}$Ge(${}^3$He,$t$)${}^{76}$As charge-exchange experiment at an incident energy of 420 MeV has been performed with an energy resolution of 30 keV. The Gamow-Teller GT${}^{-}$ strength distribution in ${}^{76}$As, which is the intermediate nucleus in the double-beta ($\beta \beta$) decay of ${}^{76}$Ge, has been extracted. An unusually strong fragmentation of the GT${}^{-}$ strength is observed even at low excitation energies of $E_x⩽5\mathrm{MeV}$. By combining the data with those for GT${}^{+}$ transitions from a recent ${}^{76}$Se($d$,${}^2$He)${}^{76}$As measurement, the nuclear matrix element for the ${}^{76}$Ge $2\nu \beta \beta$ decay has been evaluated. A lack of correlation among the GT transition strengths feeding the same levels from the two different directions is observed. The impact on the ${}^{76}$Ge $2\nu \beta \beta$ decay nuclear matrix element is discussed.

Background: The determination of the scattering and reaction amplitudes of hadronic and electromagnetic probes on the single nucleon is of central importance in determining the resonance properties of the nucleon and, in turn, the confining properties of QCD.

Purpose: To achieve in a Chew-Mandelstam parametrization a unified description of single-pion photoproduction data, together with that of pion- and $\eta$-hadroproduction data, which is consistent with unitarity at the two-body level.

Methods: Energy-dependent and single-energy partial-wave analyses of pion photoproduction data have been performed and compared to previous SAID fits and multipoles and to those from the Mainz and Bonn-Gatchina groups.

Results: The new, unified fit is more economical, using fewer parameters, as a result of the consistent implementation of two-body unitarity. Some low-energy structures, not seen by other groups, are no longer present in the current CM12 fit. Additionally, its multipole phases, particularly that of $E_{0+}^{1/2}$, have changed. Photo-decay couplings extracted from CM12 are generally---although not completely---in agreement with an earlier SAID fit (SN11) and the PDG values; significant differences are seen in $N\left(1535\right)S_{11}$ and $N\left(1720\right)P_{13}$.

Inelastic scattering from ${}^{12}$C has been measured at extremely forward angles including 0 ${}^{\circ }$ using 386 MeV $\alpha$ particles to study the $\alpha$-cluster states around $E_x$ $\sim$ 10 MeV, especially the 2${}^{+}$ state predicted by the $\alpha$-cluster model. We have analyzed ($\alpha$,${\alpha }^{\prime }$) cross-section data using both peak-fitting and multipole decomposition techniques. A 2${}^{+}$ state at $E_x=$ 9.84 $\pm$ 0.06 MeV with a width of 1.01 $\pm$ 0.15 MeV is found to be submerged in the broad 0${}^{+}$ state at $E_x=$ 9.93 $\pm$ 0.03 MeV with a width of 2.71 $\pm$ 0.08 MeV. This 2${}^{+}$ state may be interpreted as the 2${}^{+}$ excitation of the Hoyle state and the $\alpha$-condensate state.

We formulate a low-energy effective theory describing phases of matter that are both solid and superfluid. These systems simultaneously break translational symmetry and the phase symmetry associated with particle number. The symmetries restrict the combinations of terms that can appear in the effective action and the lowest order terms featuring equal number of derivatives and Goldstone fields are completely specified by the thermodynamic free energy or, equivalently, by the long-wavelength limit of static correlation functions in the ground state. We show that the underlying interaction between particles that constitute the lattice and the superfluid gives rise to entrainment, and mixing between the Goldstone modes. As a concrete example we discuss the low-energy theory for the inner crust of a neutron star, where a lattice of ionized nuclei coexists with a neutron superfluid.