We conduct a systematic investigation of the nuclear collective dynamics that emerges in systems with two-body random interactions. We explore the development of the mean field and study its geometry. We investigate multipole collectivities in the many-body spectra and their dependence on the underlying two-body interaction Hamiltonian. The quadrupole-quadrupole interaction component appears to be dynamically dominating in the two-body random ensemble. This quadrupole coherence leads to rotational spectral features and thus suggests the formation of the deformed mean-field of a specific geometry.

We present the results and analysis of our investigation of the role of break-up processes on the fusion of a ${}^{12}$C${}^{6+}$ beam with a ${}^{52}$Cr target near, at, and above the Coulomb barrier. In this experiment the excitation functions of evaporation residues produced via (${}^{12}$C, 2$n$), (${}^{12}$C, pxn), (${}^{12}$C, α$xn$), and (${}^{12}$C, αpxn) channels in a ${}^{12}$C $+$ ${}^{52}$Cr reaction were measured at several beam energies ranging from ≈51 to 87 MeV by employing the recoil catcher technique followed by off-line γ-ray spectrometry. The measured excitation functions were compared with theoretical values obtained using the pace4 statistical model code. Further, for a (${}^{12}$C, $p$2$n$) channel the measured excitation function was compared with the predictions of the alice-91 code, which was chosen as it takes into account pre-equilibrium emissions. For non-α-emitting channels, the experimentally measured excitation functions—after correcting them for possible contributions from higher charge isobaric precursor decays—were, in general, found to be in good agreement with theoretical predictions. However, for α-emitting channels, the measured excitation functions had significantly more production cross sections than what pace4 predicted. This enhancement may be attributed to incomplete fusion processes. An attempt was made to estimate the incomplete fusion fraction in order to compare the relative importance of complete and incomplete fusion processes. The incomplete fusion fraction was found to be sensitive to the projectile energy and mass asymmetry of the entrance channel. We also discuss the results in terms of the impact of the frozen α-cluster structure of the ${}^{12}$C isotope on various fusion reactions.

We present a consistent theoretical approach for the study of nonequilibrium effects in chiral fluid dynamics within the framework of the linear $\sigma$ model with constituent quarks. Treating the quarks as an equilibrated heat bath, we use the influence functional formalism to obtain a Langevin equation for the $\sigma$ field. This allows us to calculate the explicit form of the damping coefficient and the noise correlators. For a self-consistent derivation of both the dynamics of the $\sigma$ field and the quark fluid, we have to employ the 2PI (two-particle irreducible) effective action formalism. The energy dissipation from the field to the fluid is treated in the exact formalism of the 2PI effective action where a conserved energy-momentum tensor can be constructed. We derive its form and comment on approximations generating additional terms in the energy-momentum balance of the entire system.

Second Fourier harmonics of jet quenching have been thoroughly explored in the literature and shown to be sensitive to the underlying jet path-length dependence of energy loss and the differences between the mean eccentricity predicted by Glauber and color glass condensate (CGC)/Kharzeev-Levin-Nardi (KLN) models of initial conditions. We compute the jet path-length dependence of energy-loss for higher azimuthal harmonics of jet-fragments in a generalized model of energy-loss for Relativistc Heavy Ion Collider energies and find, however, that even the high-$p_T$ second moment is most sensitive to the poorly known early time evolution during the first fm/$c$. Moreover, we demonstrate that higher-jet harmonics are remarkably insensitive to the initial conditions, while the different $v_n\left(N_{\text{part}}\right)$ vs $v_n^{I_{AA}}\left(N_{\text{part}}\right)$ correlations between the moments of monojet and dijet nuclear modifications factors remain a most sensitive probe to differentiate between Glauber and CGC/KLN initial state geometries of the strongly-coupled Quark-Gluon Plasma.

Substantial collective flow is observed in collisions between lead nuclei at Large Hadron Collider (LHC) as evidenced by the azimuthal correlations in the transverse momentum distributions of the produced particles. Our calculations indicate that the global $v_1$-flow, which at RHIC peaked at negative rapidities (named third flow component or antiflow), now at LHC is going to turn toward forward rapidities (to the same side and direction as the projectile residue). Potentially this can provide a sensitive barometer to estimate the pressure and transport properties of the quark-gluon plasma. Our calculations also take into account the initial state center-of-mass rapidity fluctuations, and demonstrate that these are crucial for $v_1$ simulations. In order to better study the transverse momentum flow dependence we suggest a new “symmetrized” $v_1^S\left(p_t\right)$ function, and we also propose a new method to disentangle global $v_1$ flow from the contribution generated by the random fluctuations in the initial state. This will enhance the possibilities of studying the collective Global $v_1$ flow both at the STAR Beam Energy Scan program and at LHC.

Time reversal invariance violating and parity conserving effects for low-energy elastic neutron-deuteron scattering are calculated for meson exchange and effective field theory type potentials in a distorted wave-born approximation using realistic hadronic wave functions, obtained by solving three-body Faddeev equations in configuration space.

We present Green’s function Monte Carlo calculations of spectroscopic overlaps for $A⩽7$ nuclei. The realistic Argonne $v_{18}$ two-nucleon and Illinois-7 three-nucleon interactions are used to generate the nuclear states. The overlap matrix elements are extrapolated from mixed estimates between variational Monte Carlo and Green’s function Monte Carlo wave functions. The overlap functions are used to obtain spectroscopic factors and asymptotic normalization coefficients, and they can serve as an input for reaction calculations.

Heavy-ion collisions create deformed quark-gluon plasma (QGP) fireballs which explode anisotropically. The viscosity of the fireball matter determines its ability to convert the initial spatial deformation into momentum anisotropies that can be measured in the final hadron spectra. A quantitatively precise empirical extraction of the QGP viscosity thus requires a good understanding of the initial fireball deformation. This deformation fluctuates from event to event, and so does the finally observed momentum anisotropy. We present a harmonic decomposition of the initial fluctuations in shape and orientation of the fireball and perform event-by-event (2 + 1)-dimensional ideal fluid dynamical simulations to extract the resulting fluctuations in the magnitude and direction of the corresponding harmonic components of the final anisotropic flow at midrapidity. The final harmonic flow coefficients are found to depend nonlinearly on the initial harmonic eccentricity coefficients. We show that, on average, initial density fluctuations suppress the buildup of elliptic flow relative to what one obtains from a smooth initial profile of the same eccentricity and discuss implications for the phenomenological extraction of the QGP shear viscosity from experimental elliptic flow data.

The rise time of stellar x-ray bursts is a signature of thermonuclear runaway processes in the atmosphere of neutron stars and is highly sensitive to a series of ($\alpha$,$p$) reactions via high-lying resonances in $sd$-shell nuclei. Lacking data for the relevant resonance levels, the stellar reaction rates have been calculated using statistical, Hauser-Feshbach models, assuming a high-level density. This assumption may not be correct in view of the selectivity of the ($\alpha$,$p$) reaction to natural parity states. We measured the ${}^{28}$Si($p$,$t$)${}^{26}$Si reaction with a high-resolution spectrometer to identify resonance levels in ${}^{26}$Si above the $\alpha$-emission threshold at 9.164 MeV excitation energy. These resonance levels are used to calculate the stellar reaction rate of the ${}^{22}$Mg($\alpha$,$p$)${}^{25}$Al reaction and to test the validity of the statistical assumption.

In Israel-Stewart’s theory of dissipative hydrodynamics, we have analyzed the recent ALICE data for the centrality dependence of charged particle multiplicity, centrality dependence of integrated elliptic flow, and 0%–5% charged particle $p_T$ spectra in ${\sqrt{s}}_{NN}=$ 2.76 TeV Pb+Pb collisions and determined the initial or the thermalization time. Analysis indicates that the ALICE data disfavor very early thermalization ${\tau }_i=$ 0.2 fm, or very late thermalization ${\tau }_i$ $=$ 4 fm. Data are best explained for thermalization time ${\tau }_i={0.88}_{+0.68}^{-0.14}$ fm.

In stellar helium burning, ${}^{16}$O represents the endpoint of the helium-burning sequence due to the low rate of ${}^{16}$O($\alpha$,$\gamma$)${}^{20}$Ne. We present a new direct measurement of the total capture reaction rate of ${}^{16}$O($\alpha$,$\gamma$)${}^{20}$Ne at $E_{\mathrm{c}.\mathrm{m}.}=2.26\mathrm{MeV}$ employing the DRAGON recoil separator. For the first time, the total $S$ factor and its contributing direct capture transitions could be determined in one experiment.

The generalized density matrix method is used to calculate microscopically the parameters of the collective Hamiltonian. Higher-order anharmonicities are obtained consistently with the lowest-order results, the mean field (Hartree-Fock-Bogoliubov equation), and the harmonic potential (quasiparticle random-phase approximation). The method is applied to soft spherical nuclei, where the anharmonicities are essential for restoring the stability of the system, as the harmonic potential becomes small or negative. The approach is tested in three models of increasing complexity: the Lipkin model, model with factorizable forces, and the quadrupole plus pairing model.

The pygmy dipole resonances (PDR) for even-even nuclei in $8⩽Z⩽40$ are studied performing a systematic calculation of the random-phase approximation with the Skyrme functional of SkM*. The calculation is fully self-consistent and does not assume any symmetry in the nuclear shape of the ground state. In every isotopic chain, the PDR emerges by showing a peak of the $E1$ strength at energies less than 10 MeV. The $E1$ strength of the PDR strongly depends on the position of the Fermi level and shows a clear correlation with the occupation of the orbits with the orbital angular momenta less than $3\hslash$ ($\ell ⩽2$). We also found a strong correlation between the isotopic dependence of the neutron skin thickness and the pygmy dipole strength. The fraction of the energy-weighted strength exhausted by the PDR and the neutron skin thickness show a linear correlation with the universal rate of about 0.2 fm${}^{-1}$.

High-spin states in ${}^{125}$I have been investigated using the reaction ${}^{82}$Se(${}^{48}\text{Ca},p4n$) at a beam energy of 200 MeV and $\gamma$-ray coincidence events were detected using the Gammasphere spectrometer. A deformed rotational band, extending up to $I^{\pi }=95/2^{-}$, was observed for the first time in a heavier odd-$A$ iodine nucleus. The characteristics of the band are very similar to those of the highly deformed bands observed recently in neighboring nuclei and it is essentially identical to one of the previously known bands in ${}^{126}$Xe. The experimental results are compared to cranked Nilsson-Strutinsky calculations and possible configurations for the band are discussed.

$E2$ transitions in ${}^{30}$Si are investigated in relation to intrinsic deformations based on a method of antisymmetrized molecular dynamics. By comparing $E2$ transition strengths in the mirror nuclei ${}^{30}$Si and ${}^{30}$S, transition matrix amplitudes $M_p$ and $M_n$ for protons and neutrons are discussed in mirror analysis. Particular attention is paid to the $M_n/M_p$ ratio in the transition from the $2_2^{+}$ state to the $0_1^{+}$ state. The $M_n/M_p$ ratio in ${}^{26}$Mg and ${}^{26}$Si is also investigated. It is found that the proton dominance in the transition $2_2^{+}\to 0_1^{+}$ in ${}^{30}$Si and ${}^{26}$Si originates in the oblate trend of the $Z=14$ proton structure.

State-of-the-art signal digitization and analysis techniques have been used to measure the half-life of the Fermi $\beta$ decay of ${}^{26}$Al${}^m$. The half-life was determined to be 6347.8 $\pm$ 2.5 ms. This new datum contributes to the experimental testing of the conserved-vector-current hypothesis and the required unitarity of the Cabibbo-Kobayashi-Maskawa matrix: two essential components of the standard model. Detailed discussion of the experimental techniques and data analysis and a thorough investigation of the statistical and systematic uncertainties are presented.

We employ the equation of state of hot polarized nuclear matter to simulate the repulsive force caused by the incompressibility effects of nuclear matter in the fusion reactions of heavy colliding ions. The results of our studies reveal that temperature effects of compound nuclei have significant importance in simulating the repulsive force on the fusion reactions for which the temperature of the compound nucleus increases up to about 2 MeV. Since the equation of state of hot nuclear matter depends upon the density and temperature of the nuclear matter, it has been suggested that, by using this equation of state, one can simulate simultaneously both the effects of the precompound nucleons’ emission and the incompressibility of nuclear matter to calculate the nuclear potential in fusion reactions within a static formalism such as the double-folding (DF) model.

Even-odd effects in $Z$ and $N$ distributions of light fragments emitted at forward angles in nuclear collisions ${}^{40}$Ca $+$ ${}^{40}$Ca, ${}^{40}$Ca $+$ ${}^{48}$Ca, and ${}^{48}$Ca $+$ ${}^{48}$Ca at 25 MeV/nucleon and identified in charge and mass with the Chimera multidetector have been analyzed. The amplitude of even-odd staggering effects seems to be related to the neutron to proton ratio $N/Z$ of the entrance channels. A qualitative explanation of this effect, taking into account the deexcitation phase of primary excited fragments, is discussed.

The Compact Muon Solenoid Collaboration (CMS) has recently reported the appearance of a same-side ridge structure in two-particle angular correlations from 7-TeV $p$-$p$ collisions. The ridge in $p$-$p$ collisions at 7 TeV has been compared to a ridge structure in more-central Au-Au collisions at 200 GeV, interpreted by some as evidence for a dense, flowing QCD medium. In this study we make a detailed comparison between 200-GeV $p$-$p$ correlations and the CMS results. We find that 7-TeV minimum-bias jet correlations are remarkably similar to those at 200 GeV, even to the details of the same-side peak geometry. Appearance of a same-side ridge reflects a change in the sign of the azimuth curvature determined by the ratio of azimuth quadrupole-to-dipole amplitudes. Extrapolation of quadrupole systematics from 200 GeV suggests that the same-side ridge at 7 TeV is a manifestation of the quadrupole amplitude enhanced relative to the dipole by the energy increase and applied cuts.