The Quasi-Elastic Nuclear Response

We explore the nuclear responses at intermediate energies, particularly in the spin longitudinal and spin transverse isovector channels, within the continuum random phase approximation framework. We also employ an extension of the standard random phase approximation to account for the spreading width of the single particle states through the inclusion of a complex and energy-dependent nucleon self-energy. The nuclear responses are then used as the basic ingredient to calculate hadronic reactions in the Glauber theory framework. Here both one and two-step contributions to the multiple scattering series in the quasi-elastic peak region are taken into account. We find evidence for shell effects in the one-step response and a strong dependence on the momentum regime of the two-step contribution.Comment: 26 pages, REVTEX 2.1, 9 figures (Postscript, available from the Authors

Harmonics of the AC susceptibility as probes to differentiate the various creep models

We measured the temperature dependence of the 1st and the 3rd harmonics of the AC magnetic susceptibility on some type II superconducting samples at different AC field amplitudes, hAC. In order to interpret the measurements, we computed the harmonics of the AC susceptibility as function of the temperature T, by integrating the non-linear diffusion equation for the magnetic field with different creep models, namely the vortex glass-collective creep (single-vortex, small bundle and large bundle) and Kim-Anderson model. We also computed them by using a non-linear phenomenological I-V characteristics, including a power law dependence of the pinning potential on hAC. Our experimental results were compared with the numerically computed ones, by the analysis of the Cole-Cole plots. This method results more sensitive than the separate component analysis, giving the possibility to obtain detailed information about the contribution of the flux dynamic regimes in the magnetic response of the analysed samples.Comment: 9 pages, 6 figures, submitted to Physica

Magnetic relaxation of type II superconductors in a mixed state of entrapped and shielded flux

The magnetic relaxation has been investigated in type II superconductors when the initial magnetic state is realized with entrapped and shielded flux (ESF) contemporarily. This flux state is produced by an inversion in the magnetic field ramp rate due to for example a magnetic field overshoot. The investigation has been faced both numerically and by measuring the magnetic relaxation in BSCCO tapes. Numerical computations have been performed in the case of an infinite thick strip and of an infinite slab, showing a quickly relaxing magnetization in the first seconds. As verified experimentally, the effects of the overshoot cannot be neglected simply by cutting the first 10-100 seconds in the magnetic relaxation. On the other hand, at very long times, the magnetic states relax toward those corresponding to field profiles with only shielded flux or only entrapped flux, depending on the amplitude of the field change with respect to the full penetration field of the considered superconducting samples. In addition, we have performed numerical simulations in order to reproduce the relaxation curves measured on the BSCCO(2223) tapes; this allowed us to interpret correctly also the first seconds of the $M(t)$ curves.Comment: 9 pages, 12 figures submit to PR

Analytical approximations to the spectra of quark-antiquark potentials

A method, recently devised to obtain analytical approximations to certain classes of integrals, is used in combination with the WKB expansion to derive accurate analytical expressions for the spectrum of quantum potentials. The accuracy of our results is verified by comparing them both with the literature on the subject and with the numerical results obtained with a Fortran code. As an application of the method that we propose, we consider the meson spectroscopy with various phenomenological potentials.Comment: 12 pages, 4 figures, 1 tabl

Heavy flavours in heavy-ion collisions: quenching, flow and correlations

We present results for the quenching, elliptic flow and azimuthal correlations of heavy flavour particles in high-energy nucleus-nucleus collisions obtained through the POWLANG transport setup, developed in the past to study the propagation of heavy quarks in the Quark-Gluon Plasma and here extended to include a modeling of their hadronization in the presence of a medium. Hadronization is described as occurring via the fragmentation of strings with endpoints given by the heavy (anti-)quark Q(Qbar) and a thermal parton qbar(q) from the medium. The flow of the light quarks is shown to affect significantly the R_AA and v_2 of the final D mesons, leading to a better agreement with the experimental data. The approach allows also predictions for the angular correlation between heavy-flavour hadrons (or their decay electrons) and the charged particles produced in the fragmentation of the heavy-quark strings