$\varphi$ meson production is studied by the NA49 Collaboration in central $\mathrm{Pb}+\mathrm{Pb}$ collisions at $20A,30A,40A,80A$, and $158A$ GeV beam energy. The data are compared with measurements at lower and higher energies and with microscopic and thermal models. The energy dependence of yields and spectral distributions is compatible with the assumption that partonic degrees of freedom set in at low SPS energies.

We report on studies of the viability of using hyperon correlations as a probe of spontaneous $\mathcal{C}\mathcal{P}$ violation which it has been suggested may occur in heavy ion collisions. We discuss the motivation for such a search and use a simple model and statistical analysis to roughly estimate the size of an effect which may be expected to be visible in experiments.

We estimate the two-photon exchange contribution to the process $e^{+}+e^{-}\to p+\overline{p}\hspace{0.5em}$. The two-photon exchange corrections to double spin polarization observables and form factors in the time-like region are calculated. The corrections are found to be small in magnitude but with a strong angular dependence at fixed momentum transfer. These two features are the same as those in the space-like region. In future experiments, the double spin polarization observable $P_z$ deserves to be considered.

The helicity amplitudes of the electroexcitation of the Roper resonance are extracted for $1.7<Q^2<4.5{\mathrm{GeV}}^2$ from recent high precision JLab-CLAS cross section and longitudinally polarized beam asymmetry data for ${\pi }^{+}$ electroproduction on protons at $W=1.15-1.69$ GeV. The analysis is made using two approaches, dispersion relations and a unitary isobar model, which give consistent $Q^2$ behavior of the helicity amplitudes for the ${\gamma }^{*}p\to$N(1440)P${}_{11}$ transition. It is found that the transverse helicity amplitude $A_{1/2}$, which is large and negative at $Q^2=0$, becomes large and positive at $Q^2\simeq 2{\mathrm{GeV}}^2$, and then drops slowly with $Q^2$. The longitudinal helicity amplitude $S_{1/2}$, which was previously found from CLAS $\overrightarrow{e}p\to \mathit{ep}{\pi }^0,\mathit{en}{\pi }^{+}$ data to be large and positive at $Q^2=0.4,0.65{\mathrm{GeV}}^2$, drops with $Q^2$. Available model predictions for ${\gamma }^{*}p\to$N(1440)P${}_{11}$ allow us to conclude that these results provide strong evidence in favor of N(1440)P${}_{11}$ as a first radial excitation of the $3q$ ground state. The results of the present paper also confirm the conclusion of our previous analysis for $Q^2<1$ GeV${}^2$ that the presentation of N(1440)P${}_{11}$ as a q${}^3\mathrm{G}$ hybrid state is ruled out.

The shear viscosity of the crust might have a damping effect on the amplitude of r-modes of rotating neutron stars. This damping has implications for the emission of gravitational waves. We calculate the contribution to the shear viscosity coming from the ions using both semianalytical methods that consider binary collisions and molecular dynamics simulations. We compare these results with the contribution coming from electrons. We study how the shear viscosity depends on density for conditions of interest in neutron star envelopes and outer crusts. In the low-density limit, we find good agreement between results of our molecular dynamics simulations and those of classical semianalytic calculations.

Determination of the cross sections for stellar reaction ${}^{26}\mathrm{Si}(p,\gamma ){}^{27}\mathrm{P}$ using information about the ${}^{27}\mathrm{Mg}({\frac{3}{2}}^{+})$ mirror state can be influenced by mirror symmetry breaking in the ${}^{27}\mathrm{P}({\frac{3}{2}}^{+})\to {}^{26}\mathrm{Si}+p$ and ${}^{27}\mathrm{Mg}({\frac{3}{2}}^{+})\to {}^{26}\mathrm{Mg}+n$ amplitudes, which may arise as a threshold phenomenon due to the coupling to continuum. We study this effect within a multichannel microscopic cluster model. Our calculations confirm that such a possibility exists and suggest that the symmetry breaking in mirror decay amplitudes may become especially large if the mirror decay channels comprise only very small parts of the total wave functions. We use the estimates for mirror symmetry breaking in the ${}^{27}\mathrm{P}({\frac{3}{2}}^{+})\to {}^{26}\mathrm{Si}+p$ and ${}^{27}\mathrm{Mg}({\frac{3}{2}}^{+})\to {}^{26}\mathrm{Mg}+n$ amplitudes to derive the proton width for the astrophysically important ${}^{27}\mathrm{P}({\frac{3}{2}}^{+})$ resonance basing on the asymptotic normalization coefficient for its mirror bound state ${}^{27}\mathrm{Mg}({\frac{3}{2}}^{+})$ which we determine from the ${}^{26}\mathrm{Mg}(t,d){}^{27}\mathrm{Mg}$ reaction.

The hot nuclear matter created at the Relativistic Heavy Ion Collider has been characterized by near-perfect fluid behavior. We demonstrate that this stands in contradiction to the identification of quantum chromodynamics quasiparticles with the thermodynamic degrees of freedom in the early (fluid) stage of heavy-ion collisions. The empirical observation of constituent quark “$n_q$” scaling of elliptic flow [PHENIX, A. Adare et al., Phys. Rev. Lett. 98, 162301 (2007)] is juxtaposed with the lack of such scaling behavior in hydrodynamic fluid calculations followed by Cooper-Frye freeze-out to hadrons. As the hydrodynamic fluid expands, increasing viscous effects may allow for a short time period of “quasiparticle transport” prior to hadronization. However, without a detailed understanding of the transitions between these time stages, the “$n_q$” scaling is not a necessary consequence of this prescription. Also, if the duration of this stage is too short, it may not support well-defined quasiparticles. By comparing and contrasting the coalescence of quarks into hadrons with the similar process of producing light nuclei from nucleons, it is shown that the observation of “$n_q$” scaling in the final state does not necessarily imply that the constituent degrees of freedom were the relevant ones in the initial state.

We present the first measurements of the $\rho (770){}^0,K^{*}(892),\Delta (1232){}^{++},\Sigma (1385)$, and $\Lambda (1520)$ resonances in $d+\mathrm{Au}$ collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV, reconstructed via their hadronic decay channels using the STAR detector (the solenoidal tracker at the BNL Relativistic Heavy Ion Collider). The masses and widths of these resonances are studied as a function of transverse momentum $p_T$. We observe that the resonance spectra follow a generalized scaling law with the transverse mass $m_T$. The $\langle p_T\rangle$ of resonances in minimum bias collisions are compared with the $\langle p_T\rangle$ of $\pi ,K$, and $\overline{p}$. The ${\rho }^0/{\pi }^{-},K^{*}/K^{-},{\Delta }^{++}/p,\Sigma (1385)/\Lambda$, and $\Lambda (1520)/\Lambda$ ratios in $d+\mathrm{Au}$ collisions are compared with the measurements in minimum bias $p+p$ interactions, where we observe that both measurements are comparable. The nuclear modification factors ($R_{d\mathrm{Au}}$) of the ${\rho }^0,K^{*}$, and ${\Sigma }^{*}$ scale with the number of binary collisions ($N_{\mathrm{bin}}$) for $p_T>$ 1.2 GeV/$c$.

We construct the charge symmetry violating (CSV) nucleon-nucleon potential induced by the ${\rho }^0\text{−}\omega$ mixing due to the neutron-proton mass difference driven by the $\mathit{NN}$ loop. Analytical expression for the two-body CSV potential is presented containing both the central and noncentral $\mathit{NN}$ interaction. We show that the $\rho \mathit{NN}$ tensor interaction can significantly enhance the charge symmetry violating $\mathit{NN}$ interaction even if the momentum dependent off-shell ${\rho }^0\text{−}\omega$ mixing amplitude is considered. It is also shown that the inclusion of form factors removes the divergence arising out of the contact interaction. Consequently, we see that the precise size of the computed scattering length difference depends on how the short-range aspects of the CSV potential are treated.

Full-fledged shell-model calculations have been performed for neutron-rich Se, As, Ge, and Ga isotopes using a valence space made up from nucleons occupying the $g_{9/2},p_{1/2},p_{3/2}$, and $f_{5/2}$ orbitals. The calculated energies and electromagnetic transitions are compared with the experimental data which is available on these nuclei. Pair-truncated shell model calculations have also been carried out to investigate the structure of the high-spin states, with particular focus on the effect of the alignment of neutrons in the $g_{9/2}$ orbital.

The low-energy structures of the mirror nuclei ${}^{21}\mathrm{Ne}$ and radioactive ${}^{21}\mathrm{Na}$ have been examined by using Coulomb excitation at the TRIUMF-ISAC radioactive ion beam facility. Beams of $~5\times {10}^6$ ions/s were accelerated to 1.7 MeV/$A$ and Coulomb excited in a 0.5 mg/${\mathrm{cm}}^2$ ${}^{\mathrm{nat}}$Ti target. Scattered beam and target particles were detected by the segmented Si detector BAMBINO, while $\gamma$ rays were observed by using two TIGRESS HPGe clover detectors perpendicular to the beam axis. For each isobar, Coulomb excitation from the ${\frac{3}{2}}^{+}$ ground state to the first excited ${\frac{5}{2}}^{+}$ state was observed and $B(E2)$ values were determined by using the $2^{+}\to 0^{+}$ de-excitation in ${}^{48}\mathrm{Ti}$ as a reference. The ϕ segmentation of BAMBINO was used to deduce tentative assignments for the signs of the mixing ratios between the $E2$ and $M1$ components of the transitions. The resulting $B(E2)\uparrow$ values are $131\pm 9\hspace{0.5em}{e}^2$ ${\mathrm{fm}}^4$ ($25.4\pm 1.7$ W.u.) for ${}^{21}\mathrm{Ne}$ and $205\pm 14\hspace{0.5em}{e}^2$ ${\mathrm{fm}}^4$ ($39.7\pm 2.7$ W.u.) for ${}^{21}\mathrm{Na}$. The fit to the present data and the known lifetimes determined $E2/M1$ mixing ratios and $B(M1)\downarrow$ values of $\delta =(-)0.0767\pm 0.0027$ and $0.1274\pm 0.0025\hspace{0.5em}{\mu }_N{}^2$ and $\delta =(+)0.0832\pm 0.0028$ and $0.1513\pm 0.0017\hspace{0.5em}{\mu }_N{}^2$ for ${}^{21}\mathrm{Ne}$ and ${}^{21}\mathrm{Na}$, respectively (with Krane and Steffen sign convention). By using the effective charges $e_p=1.5e$ and $e_n=0.5e$, the $B(E2)$ values produced by the $p$-$\mathit{sd}$ shell model are 30.7 and 36.4 W.u. for ${}^{21}\mathrm{Ne}$ and ${}^{21}\mathrm{Na}$, respectively. This analysis resolves a significant discrepancy between a previous experimental result for ${}^{21}\mathrm{Na}$ and shell-model calculations.

It is shown that the Mallmann's energy ratio correlations, for the first time observed for the ground state band of the even-even nuclei, are universal: various band structures in all collective nuclei obey the same systematics, and consequently the same spin dependence. Based on a second order anharmonic vibrator description, parameter-free recurrence relations between Mallmann-type energy ratios are deduced, which can be used to extrapolate bands to higher spin.

The quasiparticle model of quark gluon plasma is the statistical mechanics of noninteracting particles with medium dependent mass related to plasma frequency, which is proposed to describe the thermodynamics of the medium itself. At the relativistic limit, the plasma frequency depends on the number density and temperature. The number density is a thermodynamic quantity of the medium which in turn depends on plasma frequency. Hence, one needs to solve this problem self-consistently instead of using perturbative expressions for plasma frequency. Here we carry out such self-consistent calculations using our recently developed new formulations of the quasiparticle model. By adjusting a single parameter for each system, a remarkably good fit to results of lattice simulation of quantum chromodynamics is obtained for 2, 3, and (2+1) flavor quark gluon plasma systems, first, with zero chemical potential. Then, it is extended to systems with finite chemical potential and fits very well to the lattice results without any new parameter.

With a proper formalism for proton emission from triaxially deformed nuclei, we perform exact calculations of decay widths for the decays to ground and first excited $2^{+}$ states in the daughter nucleus. Our results for rotational spectrum, decay width and fine structure in the case of the nucleus ${}^{145}\mathrm{Tm}$ lead for the first time to an accurate identification of triaxial deformation using proton emission. This work also puts in evidence the advantage of proton emission over the conventional probes to study nuclear structure at the proton drip-line.

The availability of new, high-intensity, cold and thermal neutron sources has opened the possibility of performing high-precision fundamental neutron physics experiments, including measurements that study the hadronic weak interaction and standard model test measurements, using neutron $\beta$ decay. The observables in these experiments are usually correlated with the direction of neutron polarization and are often very small $({10}^{-8}\to {10}^{-6})$. Mott-Schwinger scattering of polarized neutrons can produce spin-dependent shifts in beam centroids, which has the potential to produce significant systematic effects for these types of experiments. An accurate calculation of this process for neutral atoms and basic molecules has not been carried out for low neutron energies. In this work, we derive a general expression for the electromagnetic (Mott-Schwinger) contributions to the analyzing power for low-energy neutron scattering. We obtain numerical results for 11 nuclei in the range of $A=1$ to $A=208$ and provide a series of graphs for easy reference and interpolation between $A$ values. We also estimate the contribution of spin-dependent nucleon-nucleon forces and apply our results to determine the analyzing power of parahydrogen. Numerical calculations are performed to determine the analyzing power for the parahydrogen molecule and are compared to results obtained using analytical expressions.

Single-particle resonant states, also called Gamow states, as well as bound and scattering states of complex energy form a complete set, the Berggren completeness relation. It is the building block of the recently introduced Gamow shell model, where weakly bound and resonant nuclear wave functions are expanded with a many-body basis of Slater determinants generated by this set of single-particle states. However, Gamow states have never been studied in the context of Hartree-Fock-Bogoliubov theory, except in the Bardeen-Cooper-Schriefer (BCS) approximation, where both the upper and lower components of a quasiparticle wave function are assumed to possess the same radial dependence with that of a Gamow state associated with the Hartree-Fock potential. Hence, an extension of the notion of Gamow state has to be effected in the domain of quasiparticles. It is shown theoretically and numerically that bound, resonant and scattering quasiparticles are well defined and form a complete set, by which bound Hartree-Fock-Bogoliubov ground states can be constructed. It is also shown that the Gamow-Hartree-Fock single-particle basis can be used to solve the Gamow-Hartree-Fock-Bogoliubov problem. As an illustration, the proposed method is applied to neutron-rich nickel isotopes close to the neutron drip-line.

We present a unified approach to neutrino processes in nucleon matter based on Landau's theory of Fermi liquids that includes one and two quasiparticle-quasihole pair states as well as mean-field effects. We show how rates of neutrino processes involving two nucleons may be calculated in terms of the collision integral in the Landau transport equation for quasiparticles. Using a relaxation time approximation, we solve the transport equation for density and spin-density fluctuations and derive a general form for the response functions. We apply our approach to neutral-current processes in neutron matter, where the spin response function is crucial to the calculation of neutrino elastic and inelastic scattering and neutrino-pair bremsstrahlung and absorption from strongly interacting nucleons. We calculate the relaxation rates using modern nuclear interactions and including many-body contributions, and find that rates of neutrino processes are reduced compared with estimates based on the one-pion exchange interaction, which is used in current simulations of core-collapse supernovae.

The neutron capture cross sections of the Zr isotopes are relevant to studies in nuclear structure, nuclear astrophysics, and nuclear technology. The valence neutron of ${}^{91}\mathrm{Zr}$ with respect to the neutron magic nucleus ${}^{90}\mathrm{Zr}$ has interesting implications for the statistical analysis in the proximity of shell closures. In stellar nucleosynthesis, the Zr isotopes are important for the $s$-process reaction flow between the Fe seeds and the heavier isotopes. Because of its relatively small ($n,\gamma$) cross sections, Zr represents also an interesting structural material for nuclear reactors. For the same reason, these cross sections are difficult to measure and reliable data are sparse. Therefore, the ($n,\gamma$) cross sections of the Zr isotopes have been remeasured at the CERN n_TOF facility. Thanks to its high instantaneous flux, good energy resolution, and low background, this facility is particularly suited for the determination of small, resonance-dominated cross sections. In this work, results for the ${}^{91}\mathrm{Zr}$($n,\gamma$)${}^{92}\mathrm{Zr}$ reaction are reported in the neutron energy range from thermal to 26 keV. In this region, accurate data of 157 resonances could be obtained, 33 of these resonances are not present in the main databases and/or were observed for the first time.

Magnetic dipole ($M1$) transitions of $N=11$ nuclei ${}^{17}\mathrm{C}$ and ${}^{21}\mathrm{Ne}$ are investigated by using shell model and deformed Skyrme Hartree-Fock $+$ blocked BCS wave functions. Shell model calculations predict well observed energy spectra and magnetic dipole transitions in ${}^{21}\mathrm{Ne}$, while the results are rather poor to predict these observables in ${}^{17}\mathrm{C}$. In the deformed HF calculations, the ground states of the two nuclei are shown to have large prolate deformations close to ${\beta }_2=0.4$. It is also pointed out that the first $K^{\pi }=1/2^{+}$ state in ${}^{21}\mathrm{Ne}$ is prolately deformed, while the first $K^{\pi }=1/2^{+}$ state in ${}^{17}\mathrm{C}$ is predicted to have a large oblate deformation close to the ground state in energy, We point out that the experimentally observed large hindrance of the $M1$ transition between $I^{\pi }=1/2^{+}$ and $3/2^{+}$ in ${}^{17}\mathrm{C}$ can be attributed to a shape coexistence near the ground state of ${}^{17}\mathrm{C}$.

Possible decay pathways associated with three candidates for triaxial strongly deformed (TSD) bands in ${}^{168}\mathrm{Hf}$ have been investigated. The spin and excitation energy of the strongest band, TSD1, were determined approximately based on $\gamma$-ray coincidence relationships. Discrete links were established for the second band. The overall agreement between the observed properties of the bands and cranking calculations using the ULTIMATE CRANKER code provides strong support for an interpretation where band TSD1 is associated with a TSD minimum, $({\varepsilon }_2,\gamma )~(0.43,{20}^{°})$, involving the $\pi (i_{13/2}){}^2$ and the $\nu (j_{15/2})$ high-$j$ orbitals. This constitutes the first identification of a TSD band in Hf isotopes, which has been long-predicted by theoretical studies. The second band is understood as being associated with a near-prolate shape and a deformation enhanced with respect to the normal deformed bands. It is proposed to be built on the $\pi (i_{13/2}{h}_{9/2})\otimes \nu (i_{13/2}){}^2$ configuration.