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W. M. Alberico

Publications and source records attributed to W. M. Alberico.

At least 73 records · Page 4Linked to original sources
arXiv2000

Non-extensive statistics effects in quark-gluon plasma and in relativistic heavy-ion collisions

The presence of memory effects and color long-range forces among the many-parton system in the early stage of heavy-ion collisions can affect the particle statistical behavior at the freeze-out temperature. In this context, we calculate, in the framework of the equilibrium generalized non-extensive thermostatistics, the shape of pion transverse mass spectrum and the value of the transverse momentum correlation function of the pions emitted during the central Pb+Pb collisions and we show that the experimental results is well reproduced assuming very small deviations from the standard statistics.

nucl-th↗
arXiv2000

The Delta I=1/2 rule in non-mesonic weak decay of Lambda-hypernuclei

By employing recent data on non-mesonic decay of s-shell Lambda-hypernuclei we study, within the phenomenological model of Block and Dalitz, the validity of the Delta I=1/2 rule in the Lambda N--> NN process. Due to the low experimental precision, a possible violation of this rule can be neither proved nor excluded at present with sufficient accuracy: a pure Delta I=1/2 transition amplitude is excluded at 40% confidence level.

nucl-th↗
arXiv2000

Is it possible to determine the S-factor of the hep process from a laboratory experiment?

We discuss the problem of solar hep neutrinos originating from the reaction p + 3He -> 4He + e+ + nu and obtain a relation between the astrophysical S-factor of the hep process and the cross section of the process e- + 4He -> 3H + n + nu near threshold. The relation is based on the isotopic invariance of strong interactions. The measurement of the latter cross section would allow to obtain experimental information on S(hep), the value of which, at the moment, is known only from theoretical calculations.

hep-ph↗
arXiv1999

Non-extensive statistics, fluctuations and correlations in high energy nuclear collisions

Starting from the experimental evidence that high-energy nucleus-nucleus collisions cannot be described in terms of superpositions of elementary nucleon-nucleon interactions, we analyze the possibility that memory effects and long-range forces imply a nonextensive statistical regime during high energy heavy ion collisions. The relevance of these statistical effects and their compatibility with the available experimental data are discussed. In particular we show that theoretical estimates, obtained in the framework of the generalized nonextensive thermostatistics, can reproduce the shape of the pion transverse mass spectrum and explain the different physical origin of the transverse momentum correlation function of the pions emitted during the central Pb+Pb and during the p+p collisions at 158 A GeV.

nucl-th↗
arXiv1999

Functional approach to the non-mesonic decay of Lambda-hypernuclei

We present an evaluation of the non-mesonic decay widths for Lambda-hypernuclei (Lambda N --> NN, Lambda NN --> NNN) within the framework of the polarization propagator method. The full Lambda self-energy is evaluated microscopically in nuclear matter by using the functional approach, which supplies a theoretically well grounded approximation scheme for the classification of the relevant diagrams, according to the prescriptions of the bosonic loop expansion. We employ average Fermi momenta, suitably adapted to different mass number regions (medium-light, medium and heavy hypernuclei). Moreover, we study the dependence of the decay rates on the NN and Lambda-N short range correlations. With a proper choice of the parameters which control these correlations in the new approximation scheme, it is possible to reproduce the experimental decay widths for A > 10 hypernuclei.

nucl-th↗
arXiv1999

New developments in neutrino physics

A review of the problem of neutrino mass, mixing and oscillations is given. Possible phenomenological schemes of neutrino mixing are discussed. The most important consequences of neutrino mixing--neutrino oscillations are considered in some details. The data of atmospheric, solar and LSND experiments are discussed. The results of phenomenological analyses of the data under the assumption of the mixing of three and four massive neutrinos are shortly presented.

hep-ph↗
arXiv1999

Weak decays of medium and heavy Lambda-hypernuclei

We have made a new evaluation of the Lambda decay width in nuclear matter within the Propagator Method. Through the Local Density Approximation it is possible to obtain results in finite nuclei. We have also studied the dependence of the widths on the N-N and Lambda-N short range correlations. Using reasonable values for the parameters that control these correlations, as well as realistic nuclear densities and Lambda wave functions, we reproduce, for the first time, the experimental non-mesonic widths in a wide range of mass numbers (from medium to heavy hypernuclei).

nucl-th↗
arXiv1998

Strange form factors of the proton: a new analysis of the neutrino (antineutrino) data of the BNL-734 experiment

We consider ratios of elastic neutrino(antineutrino)-proton cross sections measured by the Brookhaven BNL-734 experiment and use them to obtain the neutral current (NC) over charged current (CC) neutrino-antineutrino asymmetry. We discuss the sensitivity of these ratios and of the asymmetry to the electric, magnetic and axial strange form factors of the nucleon and to the axial cutoff mass M_A. We show that the effects of the nuclear structure and interactions on the asymmetry and, in general, on ratios of cross sections are negligible. We find some restrictions on the possible values of the parameters characterizing the strange form factors. We show that a precise measurement of the neutrino-antineutrino asymmetry would allow the extraction of the axial and vector magnetic strange form factors in a model independent way. The neutrino-antineutrino asymmetry turns out to be almost independent on the electric strange form factor and on the axial cutoff mass.

hep-ph↗
arXiv1998

The ratio of p and n yields in NC neutrino(antineutrino)-nucleus scattering and strange form factors of the nucleon

We calculate the ratio of proton and neutron yields in NC induced neutrino(antineutrino)-nucleus inelastic scattering at neutrino energies of about 1 GeV. We show that this ratio depends very weakly on the nuclear models employed and that in the neutrino and antineutrino cases the ratios have different sensitivity to the axial and vector strange form factors; moreover, the ratio of antineutrino--nucleus cross sections turns out to be rather sensitive to the electric strange form factor. We demonstrate that measurements of these ratios will allow to get information on the strange form factors of the nucleon in the region Q > 0.4 GeV^2.

hep-ph↗
arXiv1997

The semi-classical approach to the exclusive electron scattering

The semiclassical approach, successfully applied in the past to the inelastic, inclusive electron scattering off nuclei, is extended to the treatment of exclusive processes. The final states interaction is accounted for in the mean field approximation, respecting the Pauli principle. The impact on the exclusive cross section of the shape of the potential binding the nucleons into the nucleus and of the distortion of the outgoing nucleon wave are explored. The exclusive scattering is found to be quite sensitive to the mean field final states interaction, unlike the inclusive one. Indeed we verify that the latter is not affected, as implied by unitarity, by the distortion of the outgoing nucleon wave except for the effect of relativity, which is modest in the range of momenta up to about 500 MeV/c. Furthermore, depending upon the correlations between the directions of the outgoing and of the initial nucleon, the exclusive cross-section turns out to be remarkably sensitive to the shape of the potential binding the nucleons. These correlations also critically affect the domain in the missing energy-- missing momentum plane where the exclusive process occurs.

nucl-th↗
arXiv1997

Inelastic neutrino and antineutrino scattering on nuclei and ``strangeness'' of the nucleon

Possibilities to extract information on the strange form factors of the nucleon from neutrino (antineutrino) inelastic scattering on nuclei, in an energy range from 200 MeV to 1 GeV and more, are investigated in detail. All calculations are performed within two relativistic independent particle models (Fermi gas and shell model); the final state interactions of the ejected nucleon are taken into account through relativistic optical model potentials. We have shown that the values of the cross sections significantly depend on the nuclear model (especially in the lower energy range). However the NC/CC neutrino-antineutrino asymmetry in a medium--high energy range shows a rather small dependence on the model and allows to disentangle different values of the parameters that characterize the strange form factors. We have calculated also the ratio of the cross sections for inelastic NC scattering of neutrinos on nuclei, with the emission of a proton and of a neutron. Our calculations show that this ratio depends rather weakly on the nuclear model and confirm previous conclusions on the rather strong dependence of this ratio upon the axial strange form factors.

hep-ph↗
arXiv1996

Possible tests of the "strangeness" of the nucleon

The NC and CC scattering of neutrino(antineutrino) on protons and nuclei with isotopic spin equal to zero is considered. It is shown that the measurement of the neutrino-antineutrino asymmetry in these processes could allow to obtain model-independent information about the contribution of the axial strange current to the cross sections of the NC processes.

hep-ph↗
arXiv1996

Inclusive neutrino and antineutrino processes and the problem of the spin of proton

The inclusive NC and CC neutrino(antineutrino)-nucleus scattering for the case of a nucleus with isotopic spin equal to zero is considered. It is shown that the measurement of the neutrino-antineutrino asymmetry at relatively small energies could allow to obtain model-independent information about the contribution of the axial strange current to the cross sections of the NC processes.

hep-ph↗
arXiv1995

Elastic Neutrino-Nucleon and Antineutrino-Nucleon Scattering and Strange Form Factors of the Nucleons

Elastic scattering of neutrinos and antineutrinos on nucleons is considered. It is shown that the measurement of the neutrino-antineutrino asymmetry would allow to obtain model independent informations on the strange axial and vector form factors. The ratio of the magnetic form factors of the proton and neutron, on which the asymmetry depends, is investigated in detail. The asymmetry is calculated under different assumptions on the behavior of the strange vector and axial form factors.

hep-ph↗
arXiv1995

Deconfinement transition in a one-dimensional model at finite temperature

We present a model for quark matter with a density dependent quark-quark (confining) potential, which allows to describe a deconfinement phase transition as the system evolves from a low density assembly of bound structures to a high density free Fermi gas of quarks. A proper account of the many-body correlations induced by the medium is crucial in order to disentangle this behaviour, which does not uniquely stem from the the naive density dependence of the interaction. We focus here on the effects of finite (non-zero) temperatures on the dynamical behaviour of the system. In particular we investigate the ground state energy per particle and the pair correlation function, from which one can extract the relevant information about the quarks being confined or not; the temperature dependence of the transition density is also derived.

hep-ph↗