Jet energy loss, photon production, and photon-hadron correlations are studied together at high transverse momentum in relativistic heavy-ion collisions at Relativistic Heavy Ion Collider (RHIC) energies. The modification of hard jets traversing a hot and dense nuclear medium is evaluated by consistently taking into account induced gluon radiation and elastic collisions. The production of high-transverse-momentum photons in $\mathrm{Au}+\mathrm{Au}$ collisions at RHIC is calculated by incorporating a complete set of photon-production channels. Comparison with experimental photon production and photon-hadron correlation data is performed, using a ($3+1$)-dimensional relativistic hydrodynamic description of the thermalized medium created in these collisions. Our results demonstrate that the interaction between the hard jets and the soft medium is important for the study of photon production and of photon-hadron correlation at RHIC.

We performed a nuclear resonance fluorescence experiment to determine the energy and quantum numbers of excited states in ${}^{26}\mathrm{Mg}$. Spin-parity ambiguities of excited states in ${}^{26}\mathrm{Mg}$, the compound nucleus for the $s$-process neutron source ${}^{22}\mathrm{Ne}$($\alpha ,n$)${}^{25}\mathrm{Mg}$, result in large uncertainties in the reaction rates. The present work uses the monoenergetic $\gamma$-ray beam from the High-Intensity $\gamma$-ray Source to probe states in the excitation energy range of $E_x=10.8$ to $11.4$ MeV. Five excited states were observed and unambiguous quantum numbers were assigned at $E_x=10\hspace{0.5em}573.3(8)$ keV ($J^{\pi }=1^{-}$), $E_x=10\hspace{0.5em}647.3(8)$ keV ($J^{\pi }=1^{+}$), $E_x=10\hspace{0.5em}805.7(7)$ keV ($J^{\pi }=1^{-}$), $E_x=10\hspace{0.5em}949.1(8)$ keV ($J^{\pi }=1^{-}$), and $E_x=11\hspace{0.5em}153.5(10)$ keV ($J^{\pi }=1^{+}$). The two natural parity states, located between the $\alpha$-particle and neutron thresholds, are expected to significantly influence the rate of the competing ${}^{22}\mathrm{Ne}$($\alpha ,\gamma$)${}^{26}\mathrm{Mg}$ reaction. An important finding of this work is that the $E_x=11\hspace{0.5em}154$ keV level has unnatural parity, contrary to previous results, and thus does not contribute to the ${}^{22}\mathrm{Ne}$$+\mathrm{\alpha }$ reaction rates.

x-ray bursts are identified as thermonuclear explosions in the outer atmosphere of accreting neutron stars. The thermonuclear runaway is fueled by the $\alpha p$ process that describes a sequence of $(\alpha ,p)$ reactions triggered by the ${}^{18}\mathrm{Ne}(\alpha ,p){}^{21}\mathrm{Na}$ breakout reaction from the hot CNO cycles. We studied the level structure of the compound nucleus ${}^{22}\mathrm{Mg}$ by measuring the ${}^{24}\mathrm{Mg}(p,t){}^{22}\mathrm{Mg}$ reaction at the Grand Raiden spectrometer at Research Center for Nuclear Physics, Osaka. A large number of $\alpha$-unbound states was identified and precise excitation energies were determined. Based on shell model and $\alpha$-cluster model calculations we predict the level parameters for determining the stellar reaction rate of ${}^{18}\mathrm{Ne}(\alpha ,p){}^{21}\mathrm{Na}$ for a wide temperature range. x-ray burst simulations have been performed to study the impact of the reaction on the x-ray burst luminosity.

We show that the gauge-invariant coupling suggested by Pascalutsa removes non-pole terms from the spin-$\frac{3}{2}$ propagator only for a specific choice of free parameter. For the general case, the problem can be solved by demanding the invariance of the full Lagrangian under the point-like transformations. It is shown that apart from gauge invariance, the original Rarita-Schwinger (R-S) constraint ensures a correct number of physical degrees of freedom. This is used to constrain couplings in the various applications of the half-integer R-S theories in hadron physics.

The energy and angular dependence of double differential cross sections $d^2\sigma /d\Omega \mathit{dE}$ were measured for $p,d,t,$${}^{3,4}\mathrm{He}$, ${}^{6,7}\mathrm{Li}$, ${}^{7,9}\mathrm{Be}$, and ${}^{10,11}\mathrm{B}$ produced in collisions of 0.175 GeV protons with a Ni target. The analysis of measured differential cross sections allowed the extraction of total production cross sections for the ejectiles listed above. The shape of the spectra and angular distributions indicates the presence of other nonequilibrium processes besides the emission of nucleons from the intranuclear cascade and the evaporation of various particles from remnants of intranuclear cascade. These nonequilibrium processes consist of the coalescence of nucleons into light-charged particles during the intranuclear cascade, of the fireball emission, which contributes to the cross sections of protons and deuterons, and of the breakup of the target nucleus, which leads to the emission of intermediate mass fragments. All such processes were found earlier at beam energies 1.2, 1.9, and 2.5 GeV for Ni and Au targets; however, significant differences in the properties of these processes at high and low beam energy are observed in the present study.

Measurements of the azimuthal anisotropy of high-$p_T$ neutral pion (${\pi }^0$) production in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{{}_{\mathit{NN}}}}=200$ GeV by the PHENIX experiment are presented. The data included in this article were collected during the 2004 Relativistic Heavy Ion Collider running period and represent approximately an order of magnitude increase in the number of analyzed events relative to previously published results. Azimuthal angle distributions of ${\pi }^0$ mesons detected in the PHENIX electromagnetic calorimeters are measured relative to the reaction plane determined event-by-event using the forward and backward beam-beam counters. Amplitudes of the second Fourier component ($v_2$) of the angular distributions are presented as a function of ${\pi }^0$ transverse momentum ($p_T$) for different bins in collision centrality. Measured reaction plane dependent ${\pi }^0$ yields are used to determine the azimuthal dependence of the ${\pi }^0$ suppression as a function of $p_T$, $R_{\mathrm{AA}}(\Delta \varphi ,p_T)$. A jet-quenching motivated geometric analysis is presented that attempts to simultaneously describe the centrality dependence and reaction plane angle dependence of the ${\pi }^0$ suppression in terms of the path lengths of hypothetical parent partons in the medium. This set of results allows for a detailed examination of the influence of geometry in the collision region and of the interplay between collective flow and jet-quenching effects along the azimuthal axis.

Heavy ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC) are well described by the (nearly ideal) hydrodynamics. In the present paper, we study the propagation of perturbations induced by moving charges (jets) on top of the expanding fireball, using hydrodynamics and (dual) magnetohydrodynamics. Two experimentally observed structures, called a “cone” and a “hard ridge”, have been discovered in a dihadron correlation function with a large-$p_t$ trigger, while a “soft ridge” is a similar structure seen without a hard trigger. All three can be viewed as traces left by a moving charge in matter, on top of overall expansion. A puzzle is why those perturbations are apparently rather well preserved at the time of the fireball freeze-out. We study two possible solutions: (A) a “wave-splitting” acoustic option and (B) a “metastable electric flux tube” option. In the first case, we show that rapidly variable speed of sound under certain conditions leads to secondary sound waves, which are at freeze-out time closer to the original location and have larger intensities than the first wave. In the latter case, we rely on (dual) magnetohydrodynamics, which also predicts two cones or cylinders of the waves. We also briefly discuss metastable electric flux tubes in the near-$T_c$ phase and their relation to clustering data.

The heavy-ion, fusion-evaporation reaction ${}^{12}\mathrm{C}$(${}^{16}\mathrm{O}$$,n$) was used to identify $\gamma$-decay transitions from excited states in ${}^{27}\mathrm{Si}$ above the proton threshold. The precise level energy measurements, $J^{\pi }$ assignments, and lifetime measurements of astrophysically important ${}^{26}\mathrm{Al}{}^m+p$ resonances have allowed an evaluation of the ${}^{26}\mathrm{Al}{}^m(p,\gamma ){}^{27}\mathrm{Si}$ reaction rate. An $l_p=0$ resonance has been newly identified at a center-of-mass energy in the ${}^{26}\mathrm{Al}{}^m+p$ system of 146.3(3) keV and is expected to dominate the rate for low stellar temperatures. In addition, an $l_p=1$ resonance has been identified at 378.3(30) keV and is likely to dominate the rate at high astrophysical temperatures, such as those found in oxygen-neon novae and core-collapse supernovae.

A new version of the generalized density-dependent cluster model is presented to describe an $\alpha$ particle tunneling through a deformed potential barrier. The microscopic deformed potential is numerically constructed in the double-folding model by the multipole expansion method. The decay width is computed using the coupled-channel Schrödinger equation with outgoing wave boundary conditions. We perform a systematic calculation on $\alpha$-decay half-lives of even-even nuclei ranging from $Z=52$ to $Z=104$, including $65$ well-deformed ones. The calculated $\alpha$-decay half-lives are found to be in good agreement with the experimental values. There also exists good agreement with the available experimental branching ratios for well-deformed systems.

A systematic study of neutron-rich even-even Fe isotopes with a neutron number from 32 to 42 is carried out by using the projected shell model. Calculations are performed up to the spin $I=20$ state. Irregularities found in the yrast spectra and in $B\hspace{0.5em}(E2)$ values are discussed in terms of neutron excitations to the high-$j$ orbital $g_{9/2}$. Furthermore, the neutron two-quasiparticle structure of a low-$K$ negative-parity band and the proton two-quasiparticle structure of a high-$K$ positive-parity band are predicted to exist near the yrast region. Our study reveals a soft nature for the ground state of $N\approx 40$ isotopes and emphasizes the important role of the neutron $g_{9/2}$ orbital in determining the structure properties for both low- and high-spin states in these nuclei.

We propose a method for determining the nuclear radii for the excited states lying above the particle breakup threshold based on the diffraction model of scattering. The method is applied to analyzing the diffraction structure of the elastic and inelastic scattering of ${}^2\mathrm{He}$, ${}^3\mathrm{He}$, ${}^4\mathrm{He}$, ${}^6\mathrm{Li}$, and ${}^{12}\mathrm{C}$ ions on ${}^{12}\mathrm{C}$ at energies below 100 MeV/$A$. We study the radii of ${}^{12}\mathrm{C}$ in the excited states up to $E_x\approx 11$ MeV and show that the diffraction radii for the ground and the first $2^{+}$ ($4.44$ MeV) excited states are approximately the same. The diffraction radii for the $0_2^{+}$ ($7.65$ MeV) Hoyle state and $3^{-}$ ($9.64$ MeV) states located above the ${}^{12}\mathrm{C}$ $\to 3\alpha$ threshold are larger by $\approx 0.5$ fm. This difference does not depend on the energy or on the kind of projectiles (deuterons are an exception). This fact justifies an application of the proposed method to the determination of the root-mean-square radii of the above-threshold states. We found that the rms radii for the $0_2^{+}$ ($7.65$ MeV) and $3^{-}$ ($9.64$ MeV) states are a factor of $1.2$ larger than the rms radius for the ground state of ${}^{12}\mathrm{C}$. Also, we estimated the rms radii for the above-threshold $2^{+}$ ($9.9$ MeV), $0^{+}$ ($10.3$ MeV), and $1^{-}$ ($10.84$ MeV) states.

We investigate particle spectra and elliptic flow coefficients in relativistic heavy-ion collisions by taking into account the distortion of phase space distributions by bulk viscosity at freezeout. We first calculate the distortion of phase space distributions in a multicomponent system with Grad’s 14-moment method. We find some subtle issues when macroscopic variables are matched with microscopic momentum distributions in a multicomponent system, and we develop a consistent procedure to uniquely determine the corrections to the phase space distributions. Next, we calculate particle spectra by using the Cooper-Frye formula to see the effect of the bulk viscosity. Despite the relative smallness of the bulk viscosity, we find that it is likely to have a visible effect on particle spectra and elliptic flow coefficients. This indicates the importance of taking into account bulk viscosity together with shear viscosity to constrain the transport coefficients with better accuracy from comparison with experimental data.

In a series of two articles we present the theoretical results of $\pi N$/meson-baryon scattering in the Kadyshevsky formalism. In this article the results are given for meson exchange diagrams. On the formal side we show, by means of an example how general couplings, i.e., couplings containing multiple derivatives and/or higher spin fields, should be treated. We do this by introducing and applying the Takahashi-Umezawa and the Gross-Jackiw method. For practical purposes we introduce the $\overline{P}$ method. We also show how the Takashashi-Umezawa method can be derived using the theory of Bogoliubov and collaborators and the Gross-Jackiw method is also used to study the $n$ dependence of the Kadyshevsky integral equation. Last but not least we present the second quantization procedure of the quasiparticle in Kadyshevsky formalism.

In this article, which is the second part in a series of two, we construct tree-level baryon exchange and resonance amplitudes for $\pi N/\mathit{MB}$ scattering in the framework of the Kadyshevsky formalism. We use this formalism to formally implement absolute pair suppression, where we make use of the method of Takahashi and Umezawa. The resulting amplitudes are Lorentz invariant and causal. We continue studying the frame dependence of the Kadyshevsky integral equation using the method of Gross and Jackiw. The invariant amplitudes, including those for meson exchange, are linked to the phase shifts using the partial-wave basis.

The nucleon-nucleon bremsstrahlung reaction is investigated based on a fully gauge-invariant relativistic meson-exchange model approach. To account consistently for the complicated part of the interaction current (which at present is too demanding to be calculated explicitly), a generalized contact current is introduced following the approach of H. Haberzettl, K. Nakayama, and S. Krewald [Phys. Rev. C 74, 045202 (2006)]. The contact interaction current is constructed phenomenologically such that the resulting full bremsstrahlung amplitude satisfies the generalized Ward-Takahashi identity. The formalism is applied to describe the high-precision proton-proton bremsstrahlung data at 190 MeV obtained at KVI [H. Huisman et al., Phys. Rev. C 65, 031001(R) (2002)]. The present results show good agreement with the data, thus removing the long-standing discrepancy between the theoretical predictions and experimental data. The present investigation, therefore, points to the importance of properly taking into account the interaction current for this reaction.

We study nucleon momentum distributions of even-even isotopes of Ni, Kr, and Sn in the framework of deformed self-consistent mean-field Skyrme HF$\hspace{0.5em}+\hspace{0.5em}$BCS method, as well as of theoretical correlation methods based on light-front dynamics and local density approximation. The isotopic sensitivities of the calculated neutron and proton momentum distributions are investigated together with the effects of pairing and nucleon-nucleon correlations. The role of deformation on the momentum distributions in even-even Kr isotopes is discussed. For comparison, the results for the momentum distribution in nuclear matter are also presented.

A set of global optical potentials has been derived to describe the interactions of ${}^6\mathrm{He}$ at low energies. The elastic scattering angular distribution data measured so far for many systems, ranging from ${}^{12}\mathrm{C}$ to ${}^{209}\mathrm{Bi}$, have been considered within the framework of the optical model to find a global potential set to describe the experimental data consistently. We report that very good agreement between theoretical and experimental results has been obtained with small ${\chi }^2/N$ values by using the derived potential set. The reaction cross section and volume integrals of the potentials have been deduced from the theoretical calculations for all studied systems at relevant energies.

A fully self-consistent microscopic framework for the evaluation of nuclear weak-interaction rates at finite temperature is introduced, based on Skyrme functionals. The single-nucleon basis and the corresponding thermal occupation factors of the initial nuclear state are determined in the finite-temperature Skyrme Hartree-Fock model and charge-exchange transitions to excited states are computed using the finite-temperature random-phase approximation (RPA). Effective interactions are implemented self-consistently: Both the finite-temperature single-nucleon Hartree-Fock equations and the matrix equations of RPA are based on the same Skyrme energy density functional. Using a representative set of Skyrme functionals, the model is applied in the calculation of stellar electron-capture cross sections for selected nuclei in the iron mass group and for neutron-rich Ge isotopes.

The Coulomb-modified Glauber model is employed to calculate the total reaction cross section $({\sigma }_R)$ for $\alpha$ particles from ${}^9\mathrm{Be}$, ${}^{12}\mathrm{C}$, ${}^{16}\mathrm{O}$, ${}^{28}\mathrm{Si}$, ${}^{40}\mathrm{Ca}$, ${}^{58,60}\mathrm{Ni}$, ${}^{112,116,120,124}\mathrm{Sn}$, and ${}^{208}\mathrm{Pb}$ at $117.2$, $163.9$, and $192.4$ MeV and from the lighter nuclei also at $69.6$ MeV. Our main focus in this work is to assess the suitability of semiphenomenological parametrization of the $\mathit{NN}$ amplitude (SP$\mathit{NN}$), used recently [Deeksha Chauhan and Z. A. Khan, Eur. Phys. J. A 41, 179 (2009)], in the analysis of ${\sigma }_R$ at the energies under consideration. Using the realistic form factors for the colliding nuclei, it is found that the SP$\mathit{NN}$ works reasonably well and we have quite a satisfactory account of the ${\sigma }_R$ data in all the cases. Moreover, our analysis suggests that the SP$\mathit{NN}$ could be taken as fairly stable to describe simultaneously the elastic angular distribution and the ${\sigma }_R$ for a wide range of target nuclei in the relatively low-energy region.