55 research outputs found
Hadron-nucleon Total Cross Section Fluctuations from Hadron-nucleus Total Cross Sections
The extent to which information about fluctuations in hadron-nucleon total
cross sections in the frozen approximation can be extracted from very high
energy hadron-nucleus total cross section measurements for a range of heavy
nuclei is discussed. The corrections to the predictions of Glauber theory due
to these fluctuations are calculated for several models for the distribution
functions, and differences of the order of 50 mb are found for heavy nuclei.
The generating function for the moments of the hadron-nucleon cross section
distributions can be approximately determined from the derivatives of the
hadron-nucleus total cross sections with respect to the nuclear geometric cross
section. The argument of the generating function, however, it limited to the
maximum value of a dimensionless thickness function obtained at zero impact
parameter for the heaviest nuclear targets: about 1.8 for pions and 3.0 for
nucleons.Comment: 14 pages, revtex 3.0, 4 figures available upon reques
Proton-nucleus scattering and cross section fluctuations at RHIC and LHC
We consider high-energy proton-heavy nucleus scattering within the framework
of the Glauber-Gribov approximation and taking into account cross section
fluctuations. Fixing parameters of the model for cross section fluctuations by
the available data, we make predictions for the total, elastic and coherent
diffractive dissociation proton-nucleus cross sections for the RHIC and LHC
energy range. We predict a strong change of the A-dependence of diffraction
dissociation from A^{0.42} at RHIC energies to A^{0.27} at LHC energies.
Based on the obtained results, we discuss the approach of the interactions to
the black body (unitarity) limit. We estimate the electromagnetic contribution
to coherent pA diffraction and find that it dominates the coherent diffractive
cross section on heavy nuclear targets in the RHIC and LHC kinematics.Comment: 18 pages, LaTeX, 1 table, 4 figures. This is the final version
published in Phys. Lett. B 633 (2006) 245, with recent corrections published
as Erratum in Phys. Lett. B 663 (2008) 456. The Erratum concerns Section 5 of
the paper: we corrected the Lorentz factor for the calculation of the e.m.
contribution and modified Fig.
Transition to resonance-rich matter in heavy ion collisions at RHIC energies
The equilibration of hot and dense nuclear matter produced in the central
region in central Au+Au collisions at AGeV is studied within the
microscopic transport model UrQMD. The pressure here becomes isotropic at fm/c. Within the next 15 fm/c the expansion of the matter proceeds
almost isentropically with the entropy per baryon ratio .
During this period the equation of state in the -plane has a very
simple form, . Comparison with the statistical model (SM) of
an ideal hadron gas reveals that the time of fm/ may be too
short to attain the fully equilibrated state. Particularly, the fractions of
resonances are overpopulated in contrast to the SM values. The creation of such
a long-lived resonance-rich state slows down the relaxation to chemical
equilibrium and can be detected experimentally.Comment: Talk at the conference Strangeness'2000, to be published in J. of
Phys.
Heavy Ion Collisions at Relativistic Energies: Testing a Nuclear Matter at High Baryon and Isospin Density
We show that the phenomenology of isospin effects on heavy ion reactions at
intermediate energies (few AGeV range) is extremely rich and can allow a
``direct'' study of the covariant structure of the isovector interaction in the
hadron medium. We work within a relativistic transport frame, beyond a cascade
picture, consistently derived from effective Lagrangians, where isospin effects
are accounted for in the mean field and collision terms. Rather sensitive
observables are proposed from collective flows (``differential'' flows) and
from pion/kaon production (, yields). For the latter
point relevant non-equilibrium effects are stressed. The possibility of the
transition to a mixed hadron-quark phase, at high baryon and isospin density,
is finally suggested. Some signatures could come from an expected ``neutron
trapping'' effect.Comment: 8 pages, 4 figures, espcrc1 (latex) style. Conf. "Perspectives in
Hadronic Physics", ICTP Trieste May 2006, Nucl.Phys. A, to appea
Interaction of small size wave packet with hadron target
We calculate in QCD the cross section for the scattering of an energetic
small-size wave packet off a hadron target. We use our results to study the
small- behaviour of , the distribution over cross
section for the pion, in the leading -order.Comment: Revised version of the report CEBAF-TH-96-0
Isospin Dynamics in Heavy Ion Collisions: EoS-sensitive Observables
Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium
nuclear interaction in regions away from saturation and at high nucleon
momenta. In this report we present a selection of reaction observables
particularly sensitive to the isovector part of the interaction, i.e. to the
symmetry term of the nuclear Equation of State (EoS) At low energies the
behavior of the symmetry energy around saturation influences dissipation and
fragment production mechanisms. Predictions are shown for deep-inelastic and
fragmentation collisions induced by neutron rich projectiles. Differential flow
measurements will also shed lights on the controversial neutron/proton
effective mass splitting in asymmetric matter. The high density symmetry term
can be derived from isospin effects on heavy ion reactions at relativistic
energies (few AGeV range), that can even allow a ``direct'' study of the
covariant structure of the isovector interaction in the hadron medium. Rather
sensitive observables are proposed from collective flows and from pion/kaon
production. The possibility of the transition to a mixed hadron-quark phase, at
high baryon and isospin density, is finally suggested. Some signatures could
come from an expected ``neutron trapping'' effect.Comment: 10 pages, 5 figures; espcrc1 style; IX Int.Conf. on Nucleus-Nucleus
Collisions, Rio de Janeiro Aug.2006; to appear in Nucl.Phys.
Isospin Effects on Strangeness in Heavy-Ion Collisions
Kaon properties are studied within the framework of a fully covariant
transport approach. The kaon-nucleon potential is evaluated in two schemes, a
chiral perturbative approach and an effective One-Boson-Exchange model. Isospin
effects are explicitly accounted for in both models. The transport calculations
indicate a significant sensitivity of momentum distributions and total yields
of isospin states on the choice of the kaon-nucleon interaction.
Furthermore, isospin effects are rather moderate on absolute kaon yields, but
appear on strangeness ratios. This is an important issue in determining the
high density symmetry energy from studies of strangeness production in
heavy-ion collisions.Comment: 15 papes, 5 figures. Accepted for publication in Nuclear Physic
Electroproduction of Charmonia off Nuclei
In a recent publication we have calculated elastic charmonium production in
ep collisions employing realistic charmonia wave functions and dipole cross
sections and have found good agreement with the data in a wide range of s and
Q^2. Using the ingredients from those calculations we calculate exclusive
electroproduction of charmonia off nuclei. Here new effects become important,
(i) color filtering of the c-cbar pair on its trajectory through nuclear
matter, (ii) dependence on the finite lifetime of the c-cbar fluctuation
(coherence length) and (iii) gluon shadowing in a nucleus compared to the one
in a nucleon. Total coherent and incoherent cross sections for C, Cu and Pb as
functions of s and Q^2 are presented together with some differential cross
sections. The results can be tested with future electron-nucleus colliders or
in peripheral collisions of ultrarelativistic heavy ions.Comment: 21 pages of Latex including 14 figures; few misprints are fixe
On the Lorentz structure of the symmetry energy
We investigate in detail the density dependence of the symmetry energy in a
relativistic description by decomposing the iso-vector mean field into
contributions with different Lorentz covariant properties. We find important
effects of the iso-vector, scalar channel (i.e. -meson like) on the
high density behavior of the symmetry energy. Applications to static properties
of finite nuclei and to dynamic situations of heavy ion collisions are explored
and related to each other. The nuclear structure studies show only moderate
effects originating from the virtual meson. At variance, in heavy ion
collisions one finds important contributions on the reaction dynamics arising
from the different Lorentz structure of the high density symmetry energy when a
scalar iso-vector field is introduced. Particularly interesting is the
related neutron/proton effective mass splitting for nucleon transport effects
and for resonance and particle production around the threshold. We show that
the -like channel turns out to be essential for the production of
pions, when comparing with experimental data, in particular for high momentum
selections.Comment: 30 pages, 12 figures (.eps
Diffractive Leptoproduction of Vector Mesons in QCD
We demonstrate that the distinctive features of the forward differential
cross section of diffractive leptoproduction of a vector meson can be
legitimately calculated in perturbative QCD in terms of the light-cone wave function of the vector meson and the gluon distribution of the target.
In particular, we calculate the and nuclear dependence of the diffractive
leptoproduction of vector mesons and estimate the cross section. The production
of longitudinally polarized vector mesons by longitudinally polarized virtual
photons is predicted to be the dominant component, yielding a cross section
behaving as . The nuclear dependence of the diffractive cross sections,
which follows from a factorization theorem in perturbative QCD, provides
important tests of color transparency as well as constraints on the shadowing
of the gluon structure functions and the longitudinal structure functions of
nuclei.Comment: 32 pages, requires phyzzx.tex, figures can be obtained by sending
preprint request to SLAC, minor clarifications and additional references
incorporated in revised version, preprint SLAC-PUB-641
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