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.

We perform Brueckner-Hartree-Fock calculations of hypernuclear matter at finite temperature and provide convenient analytical parametrizations of the results. We then study the properties of (proto)neutron stars containing hyperons. We find important effects of trapping and finite temperature on the structure of hyperonic stars.

We study the development of collectivity in the neutron-rich nuclei around $N=40$, where the experimental and theoretical evidence suggest a rapid shape change from the spherical to the rotational regime, in analogy to what happens at the island of inversion surrounding ${}^{31}\mathrm{Na}$. Theoretical calculations are performed within the interacting shell-model framework in a large valence space, based on a ${}^{48}\mathrm{Ca}$ core, which encompasses the full $\mathit{pf}$ shell for the protons and the $0f_{5/2}$, $1p_{3/2}$, $1p_{1/2}$, $0g_{9/2}$, and $1d_{5/2}$ orbits for the neutrons. The effective interaction is based on a G matrix obtained from a realistic nucleon-nucleon potential whose monopole part is corrected empirically to produce effective single-particle energies compatible with the experimental data. We find a good agreement between the theoretical results and the available experimental data. We predict the onset of deformation at different neutron numbers for the various isotopic chains. The maximum collectivity occurs in the chromium isotopes where the large deformation regime already starts at $N=38$. The shell evolution responsible for the observed shape changes is discussed in detail, in parallel to the situation in the $N=20$ region.

We present simple equations for a canonical-basis (Cb) formulation of the time-dependent Hartree-Fock-Bogoliubov (TDHFB) theory. The equations are obtained from the TDHFB theory with an approximation that the pair potential is assumed to be diagonal in the Cb. The Cb formulation significantly reduces the computational cost. We apply the method to linear-response calculations for even-even light nuclei and demonstrate its capability and accuracy by comparing our results with recent calculations of the quasiparticle random-phase approximation with Skyrme functionals. We show systematic studies of $E1$ strength distributions for Ne and Mg isotopes. The evolution of the low-lying pygmy strength seems to be determined by the interplay of several factors, which include the neutron excess, the separation energy, the neutron-shell effects, the deformation, and the pairing.

The structure of proton unbound ${}^{30}\mathrm{S}$ states is important for determining the ${}^{29}\mathrm{P}$($p,\gamma$)${}^{30}\mathrm{S}$ reaction rate, which influences explosive hydrogen burning in classical novae and type I x-ray bursts. The reaction rate in this temperature regime had been previously predicted to be dominated by two low-lying, unobserved, $J^{\pi }=$ $3^{+}$ and $2^{+}$ resonances above the proton threshold in ${}^{30}\mathrm{S}$. To search for these levels, the structure of ${}^{30}\mathrm{S}$ was studied using the ${}^{32}\mathrm{S}$($p,t$)${}^{30}\mathrm{S}$ transfer reaction with a magnetic spectrograph. We have confirmed a previous detection of a state near 4700 keV, which had tentatively been assigned $J^{\pi }=3^{+}$. We have also discovered a new state at 4814(3) keV, which is a strong candidate for the other important resonance ($J^{\pi }=2^{+}$). The new ${}^{29}\mathrm{P}$($p,\gamma$)${}^{30}\mathrm{S}$ reaction rate is up to 4–20 times larger than previously determined rates over the relevant temperature range. The uncertainty in the reaction rate due to uncertainties in the resonance energies has been significantly reduced.

Excited states in the extremely neutron-deficient nucleus ${}^{180}\mathrm{Pb}$ have been identified for the first time using the JUROGAM II array in conjunction with the RITU recoil separator at the Accelerator Laboratory of the University of Jyväskylä. This study lies at the limit of what is presently achievable with in-beam spectroscopy, with an estimated cross section of only 10 nb for the ${}^{92}\mathrm{Mo}$(${}^{90}\mathrm{Zr}$,$2n$)${}^{180}\mathrm{Pb}$ reaction. A continuation of the trend observed in ${}^{182}\mathrm{Pb}$ and ${}^{184}\mathrm{Pb}$ is seen, where the prolate minimum continues to rise beyond the $N=104$ midshell with respect to the spherical ground state. Beyond-mean-field calculations are in reasonable correspondence with the trends deduced from experiment.

The precise determination of the neutron capture cross sections of ${}^{186}\mathrm{Os}$ and ${}^{187}\mathrm{Os}$ is important to define the $s$-process abundance of ${}^{187}\mathrm{Os}$ at the formation of the solar system. This quantity can be used to evaluate the radiogenic component of the abundance of ${}^{187}\mathrm{Os}$ due to the decay of the unstable ${}^{187}\mathrm{Re}$ ($t_{1/2}=41.2$ Gyr) and from this to infer the time duration of the nucleosynthesis in our galaxy (Re/Os cosmochronometer). The neutron capture cross sections of ${}^{186}\mathrm{Os}$, ${}^{187}\mathrm{Os}$, and ${}^{188}\mathrm{Os}$ have been measured at the CERN n_TOF facility from 1 eV to 1 MeV, covering the entire energy range of astrophysical interest. The measurement has been performed by time-of-flight technique using isotopically enriched samples and two ${\mathrm{C}}_6$D${}_6$ scintillation detectors for recording the prompt $\gamma$ rays emitted in the capture events. Maxwellian averaged capture cross sections have been determined for thermal energies between $\mathit{kT}=5$ and 100 keV corresponding to all possible $s$-process scenarios. The estimated uncertainties for the values at 30 keV are 4.1, 3.3, and $4.7\%$ for ${}^{186}\mathrm{Os}$, ${}^{187}\mathrm{Os}$, and ${}^{188}\mathrm{Os}$, respectively.

The inelastic neutron-scattering cross section of ${}^{187}\mathrm{Os}$ has been determined in a time-of-flight experiment at the Karlsruhe $3.7$-MV Van de Graaff accelerator. An almost monoenergetic beam of 30-keV neutrons was produced at the threshold of the ${}^7\mathrm{Li}$($p,n$)${}^7\mathrm{Be}$ reaction. Information on the inelastic channel is required for reliable calculations of the so-called stellar enhancement factor, by which the laboratory cross section of ${}^{187}\mathrm{Os}$ must be corrected in order to account for the thermal population of low-lying excited states at the temperatures of $s$-process nucleosynthesis, in particular of the important state at 9.75 keV. This correction represents a crucial step in the interpretation of the ${}^{187}\mathrm{Os}$/${}^{187}\mathrm{Re}$ pair as a cosmochronometer.

Neutron resonance analyses have been performed for the capture cross sections of ${}^{186}\mathrm{Os}$, ${}^{187}\mathrm{Os}$, and ${}^{188}\mathrm{Os}$ measured at the n_TOF facility at cern. Resonance parameters have been extracted up to 5, 3, and 8 keV, respectively, using the sammy code for a full $R$-matrix fit of the capture yields. From these results average resonance parameters were derived by a statistical analysis to provide a comprehensive experimental basis for modeling of the stellar neutron capture rates of these isotopes in terms of the Hauser-Feshbach statistical model. Consistent calculations for the capture and inelastic reaction channels are crucial for the evaluation of stellar enhancement factors to correct the Maxwellian averaged cross sections obtained from experimental data for the effect of thermally populated excited states. These factors have been calculated for the full temperature range of current scenarios of $s$-process nucleosynthesis using the combined information of the experimental data in the region of resolved resonances and in the continuum. The consequences of this analysis for the $s$-process component of the ${}^{187}\mathrm{Os}$ abundance and the related impact on the evaluation of the time duration of galactic nucleosynthesis via the Re/Os cosmochronometer are discussed.

A description of exclusive charged-pion electroproduction $(e,e^{\prime }{\pi }^{\pm })$ off nucleons at high energies is proposed. The model combines a Regge pole approach with the residual effect of nucleon resonances. The exchanges of $\pi (140)$, vector $\rho (770)$, and axial-vector $a_1(1260)$ and $b_1(1235)$ Regge trajectories are considered. The contribution of nucleon resonances is described using a dual connection between the exclusive hadronic form factors and inclusive deep inelastic structure functions. The model describes the measured longitudinal, transverse, and interference cross sections at the Thomas Jefferson Lab National Accelerator Facility (JLAB) and the Deutsches Elektronen Synchrotron. The scaling behavior of the cross sections is in agreement with JLAB and deeply virtual HERMES data. The results for a polarized beam-spin azimuthal asymmetry in $(\mathrm{e⃗},e^{\prime }{\pi }^{\pm })$ are presented. Model predictions for JLAB at $12$ GeV are given.

PHENIX has measured the $e^{+}{e}^{-}$ pair continuum in $\sqrt{s_{\mathit{NN}}}=200$ GeV $\mathrm{Au}+\mathrm{Au}$ and $p+p$ collisions over a wide range of mass and transverse momenta. The $e^{+}{e}^{-}$ yield is compared to the expectations from hadronic sources, based on PHENIX measurements. In the intermediate-mass region, between the masses of the $\varphi$ and the $J/\psi$ meson, the yield is consistent with expectations from correlated $c\mathrm{c̄}$ production, although other mechanisms are not ruled out. In the low-mass region, below the $\varphi$, the $p+p$ inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, the $\mathrm{Au}+\mathrm{Au}$ minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of $4.7\pm {0.4}^{\mathrm{stat}}\pm {1.5}^{\mathrm{syst}}\pm {0.9}^{\mathrm{model}}$. At low mass ($m_{\mathit{ee}}<0.3$ GeV/$c^2$) and high $p_T$ ($1<p_T<5$ GeV/$c$) an enhanced $e^{+}{e}^{-}$ pair yield is observed that is consistent with production of virtual direct photons. This excess is used to infer the yield of real direct photons. In central $\mathrm{Au}+\mathrm{Au}$ collisions, the excess of the direct photon yield over the $p+p$ is exponential in $p_T$, with inverse slope $T=221\pm {19}^{\mathrm{stat}}\pm {19}^{\mathrm{syst}}$ MeV. Hydrodynamical models with initial temperatures ranging from $T_{\mathrm{init}}\simeq 300–600$ MeV at times of $0.6–0.15$ fm/$c$ after the collision are in qualitative agreement with the direct photon data in $\mathrm{Au}+\mathrm{Au}$. For low $p_T<1$ GeV/$c$ the low-mass region shows a further significant enhancement that increases with centrality and has an inverse slope of $T\simeq 100$ MeV. Theoretical models underpredict the low-mass, low-$p_T$ enhancement.