Theory of inelastic lepton-nucleus scattering

This work reports the studies of the quark structure of a nucleus. Deuterium is the simplest nuclear system with weak binding energy and low average density so that it provides an ideal starting point for this study. Models based on the one photon exchange process should provide a good description of deuterium inelastic lepton scattering data. Furthermore, the available deuterium data cover the widest kinematical range among all A ≥ 2 targets. If the conventional nuclear physics picture is correct, the quasi-elastic nucleon knockout process along with nucleon inelastic processes should be able to account for the inelastic lepton scattering data. However, there are uncertainties in the deuteron wavefunctions, nucleon elastic form factors and nucleon inelastic structure functions. To understand these uncertainties and their possible role in obscuring the quark structure of the nucleus, I examined two deuteron wavefunction models: Reid Soft Core (RSC) and Bonn; three nucleon elastic form factors: Blatnik and Zovko, Hohler, and Gari and Krumpelmann; and three nucleon inelastic structure function models: Buras and Gaemers (BG), Abbott, Atwood and Barnett (AAB), and Duke and Owens (DO). The Gari and Krumpelmann nucleon form factors combining the meson dynamics at low Q[superscript]2 and QCD quark dynamics at high Q[superscript]2 should perform better in the long run, and are turned to fit available nucleon data. On the other hand the nucleon inelastic structure functions are not free of ambiguities. While the AAB and DO seem to fit data better in the higher Q[superscript]2 region, I chose BG in my deuterium calculations because it fits the nucleon inelastic data better in the kinematic region (2.5 ≤ Q[superscript]2 ≤ 8 GeV[superscript]2) where the deuterium data are analyzed. The Bonn potential is based on a more sophisticated meson exchange theory, and is believed to more accurately describe a wider spectrum of nuclear properties. The theoretical results with the RSC wavefunction agree with data fairly well, while the Bonn wavefunction opens the door to the 6-quark cluster to play an important role. With the Bonn deuterium wavefunctions I determined that the critical radius for 6-quark cluster formation R[subscript]C ~ 0.49 fm which provides a 5% probability of a 6-q cluster configuration in the ground state of deuterium

Chemical freezeout in relativistic A+A collisions: is it close to the QGP?

Preliminary experimental data for particle number ratios in the collisions of Au+Au at the BNL AGS (11A GeV/c) and Pb+Pb at the CERN SPS (160A GeV/c) are analyzed in a thermodynamically consistent hadron gas model with excluded volume. Large values of temperature, T = 140 185 MeV, and baryonic chemical potential, µb = 590 270 MeV, close to the boundary of the quark-gluon plasma phase are found from fitting the data. This seems to indicate that the energy density at the chemical freezeout is tremendous which would be indeed the case for the point-like hadrons. However, a self-consistent treatment of the van der Waals excluded volume reveals much smaller energy densities which are very far below a lowest limit estimate of the quark-gluon plasma energy density. PACS number(s): 25.75.-q, 24.10.P

Hadron production in non linear relativistic mean field models

By using a parametrization of the non-linear Walecka model which takes into account the binding energy of different hyperons, we present a study of particle production yields measured in central Au-Au collision at RHIC. Two sets of different hyperon-meson coupling constants are employed in obtaining the hadron production and chemical freeze-out parameters. These quantities show a weak dependence on the used hyperon-meson couplings. Results are in good overall accordance with experimental data. We have found that the repulsion among the baryons is quite small and, through a preliminary analysis of the effective mesonic masses, we suggest a way to improve the fittings.Comment: 18 pages, 2 figure

Theory of inelastic lepton-nucleus scattering

This work reports the studies of the quark structure of a nucleus. Deuterium is the simplest nuclear system with weak binding energy and low average density so that it provides an ideal starting point for this study. Models based on the one photon exchange process should provide a good description of deuterium inelastic lepton scattering data. Furthermore, the available deuterium data cover the widest kinematical range among all A ≥ 2 targets. If the conventional nuclear physics picture is correct, the quasi-elastic nucleon knockout process along with nucleon inelastic processes should be able to account for the inelastic lepton scattering data. However, there are uncertainties in the deuteron wavefunctions, nucleon elastic form factors and nucleon inelastic structure functions. To understand these uncertainties and their possible role in obscuring the quark structure of the nucleus, I examined two deuteron wavefunction models: Reid Soft Core (RSC) and Bonn; three nucleon elastic form factors: Blatnik and Zovko, Hohler, and Gari and Krumpelmann; and three nucleon inelastic structure function models: Buras and Gaemers (BG), Abbott, Atwood and Barnett (AAB), and Duke and Owens (DO). The Gari and Krumpelmann nucleon form factors combining the meson dynamics at low Q[superscript]2 and QCD quark dynamics at high Q[superscript]2 should perform better in the long run, and are turned to fit available nucleon data. On the other hand the nucleon inelastic structure functions are not free of ambiguities. While the AAB and DO seem to fit data better in the higher Q[superscript]2 region, I chose BG in my deuterium calculations because it fits the nucleon inelastic data better in the kinematic region (2.5 ≤ Q[superscript]2 ≤ 8 GeV[superscript]2) where the deuterium data are analyzed. The Bonn potential is based on a more sophisticated meson exchange theory, and is believed to more accurately describe a wider spectrum of nuclear properties. The theoretical results with the RSC wavefunction agree with data fairly well, while the Bonn wavefunction opens the door to the 6-quark cluster to play an important role. With the Bonn deuterium wavefunctions I determined that the critical radius for 6-quark cluster formation R[subscript]C ~ 0.49 fm which provides a 5% probability of a 6-q cluster configuration in the ground state of deuterium.</p

The analysis of particle multiplicities in Pb+Pb collisions at CERN SPS within hadron gas models

The preliminary data on total hadron multiplicities measured by NA49 Collaboration in central Pb+Pb collisions at 158A GeV/c are analyzed. The ideal hadron gas model fails to give a reasonable explanation to the Pb+Pb data sets. We study the possible effects of strangeness suppression because of incomplete chemical equilibrium and pion enhancement due to different hard-core repulsion for pions and other hadrons. Each of these two modifications significantly improves the results. The combined effect of these two mechanisms results in an extremely good agreement with the data. An interpretation of the obtained results in terms of the possible quark-gluon plasma formation at the early stage of the collision is also discussed.The preliminary data on hadron multiplicities measured in central Pb+Pb collisions at 158A GeV/c are analyzed. The ideal hadron gas model fails to give a reasonable explanation to the Pb+Pb data sets. We study the possible effects of pion enhancement due to different hard-core repulsion for pions and other hadrons and strangeness suppression because of incomplete chemical equilibrium. Each of these two modifications improves the results. The combined effect of these two mechanisms leads to an extremely good agreement with the data. An interpretation of the obtained results in terms of the possible quark-gluon plasma formation at the early stage of the collision is also discussed

Chemical freezeout in relativistic A + A collisions: is it close to the quark-gluon plasma?

Preliminary experimental data for particle number ratios in the collisions of Au+Au at the BNL AGS (11$A$ GeV/$c$) and Pb+Pb at the CERN SPS (160$A$ GeV/$c$) are analyzed in a thermodynamically consistent hadron gas model with excluded volume. Large values of temperature, T=140--185 MeV, and baryonic chemical potential, $\mu_b=590$--270 MeV, close to the boundary of the quark-gluon plasma phase are found from fitting the data. This seems to indicate that the energy density at the chemical freezeout is tremendous which would be indeed the case for the point-like hadrons. However, a self-consistent treatment of the van der Waals excluded volume reveals much smaller energy densities which are very far below a lowest limit estimate of the quark-gluon plasma energy density.Comment: RevTeX, 11 pages, 3 figure