15 research outputs found
A unitary model for structure functions and diffractive production at small x
We propose a unified approach which describes both structure functions in the
small- region and diffractive production in -interactions. It is
shown that the model, based on reggeon calculus and a quark-parton picture of
the interaction, gives a good description of available experimental data in a
broad region of (including ) with a single Pomeron of intercept
. Predictions for very small are given and the problem
of saturation of parton densities is discussed.Comment: 43 pages, latex, 15 postscript figure
Double parton scatterings in high energy hadronic collisions
CDF has recently measured a large number of double parton scatterings. The
observed value of , the non perturbative parameter which
characterizes the process, is considerably smaller as compared with the naive
expectation. The small value of is likely to be an indication of
the importance of the two-body parton correlations in the many-body parton
distributions of the proton.Comment: 8 pages, latex file, no figures, contributions to the proceedings of
the ISMD9
Centrality Dependence of Hadron Multiplicities in Nuclear Collisions in the Dual Parton Model
We show that, even in purely soft processes, the hadronic multiplicity in
nucleus-nucleus interactions contains a term that scales with the number of
binary collisions. In the absence of shadowing corrections, this term dominates
at mid rapidities and high energies. Shadowing corrections are calculated as a
function of impact parameter and the centrality dependence of mid-rapidity
multiplicities is determined. The multiplicity per participant increases with
centrality with a rate that increases between SPS and RHIC energies, in
agreement with experiment.Comment: 15 pages, 4 postscript figure
On the electroweak phase transition in the Minimal Supersymmetric Standard Model
We study the finite-temperature effective potential of the Minimal
Supersymmetric Standard Model, in the limit of only one light Higgs boson.
Because of the large top Yukawa coupling, there can be significant differences
with respect to the Standard Model case: for given values of the Higgs and top
masses, little supersymmetry breaking in the stop sector can make the phase
transition more strongly first-order. After including the full structure of the
stop mass matrix, the most important experimental constraints and the leading
plasma effects, we find that the present limits on Higgs and squark masses are
still compatible with the scenario of electroweak baryogenesis, in a small
region of parameter space corresponding to m_h \simlt 70 \gev and \msba
\simlt 105 \gev.Comment: 10 A4 pages, 7 figures available upon request, CERN-TH.6833/93,
IEM-FT-69/93 (one paragraph expanded for clarity
Physics of the Muon Spectrometer of the ALICE Experiment
The main goal of the Muon spectrometer of the ALICE experiment at LHC is the
measurement of heavy quark production in p+p, p+A and A+A collisions at LHC
energies, via the muonic channel. Physics motivations and expected performances
have been presented in this talk.Comment: 10 pages and 4 figures. Talk presented in the ICPAQGP Conference,
February 8-12, 2005, Salt Lake City, Kolkata, India. Web page of the
conference : http://www.veccal.ernet.in/~icpaqgp
Temperature and Density Effects on the Nucleon Mass Splitting
The finite temperature and finite density dependence of the neutron-proton
mass difference is analysed in a purely hadronic framework where the
mixing is crucial for this isospin symmetry breakdown. The
problem is handled within Thermo Field Dynamics. The present results,
consistent with partial chiral and charge symmetry restoration, improve the
experimental data fit for the energy difference between mirror nuclei.Comment: 17 pages, revtex fil
Minijets and the Two-Body Parton Correlation
A large number of double parton scatterings have been recently measured by
CDF. The double parton scattering process measures , a non
perturbative quantity related to the hadronic transverse size and with the
dimensions of a cross section. The actual value measured by CDF is considerably
smaller as compared with the naive expectation, namely the value of the
inelastic non diffractive cross section. The small value of may
be an effect of the hadron structure in transverse plane. We discuss the
problem by taking into account, at all orders, the two-body parton correlations
in the many-body parton distributions.Comment: 19 pages, plane tex, no figure
Spontaneous CP Violation and Baryogenesis in the Minimal Supersymmetric Standard Model
We investigate the effects of the spontaneous CP violation at finite
temperature in the Minimal Supersymmetric Standard Model on the baryogenesis at
the weak scale. After a brief discussion of the case in which the electroweak
phase transition is of the second order, we study in details the baryogenesis
scenario when the transition proceeds via bubble nucleation. We show that the
space-time dependent phase for the Higgs vacuum expectation values coming from
the spontaneous CP violation can give rise to a efficient generation of baryon
number inside the bubble walls if the superpotential parameters and the soft
supersymmetry breaking ones are complex. However we find that in order to get
the observed value for the baryon asymmetry of the universe the phases of such
parameters can be as small as , giving rise to an electron dipole
moment of the neutron well below the current experimental limit. Moreover a
light Higgs pseudoscalar is needed, and an upper bound on its mass is obtained.Comment: 17 pages, LaTex, DFPD 93/TH/26 UTS-DFT 93/9 SISSA 93/50-