33 research outputs found
Color mixing in high-energy hadron collisions
The color mixing of mesons propagating in a nucleus is studied with the help
of a color-octet Pomeron partner present in the two-gluon model of the Pomeron.
For a simple model with four meson-nucleon channels, color mixings are found to
be absent for pointlike mesons and very small for small mesons. These results
seem to validate the absorption model with two independent color components
used in recent analyses of the nuclear absorption of mesons produced
in nuclear reactions.Comment: 3 journal-style page
The Color Dipole Picture of low-x DIS: Model-Independent and Model-Dependent Results
We present a detailed examination of the color-dipole picture (CDP) of
low- deep inelastic scattering. We discriminate model-independent results,
not depending on a specific parameterization of the dipole cross section, from
model-dependent ones. The model-independent results include the ratio of the
longitudinal to the transverse photoabsorption cross section at large , or
equivalently the ratio of the longitudinal to the unpolarized proton structure
function, , as well as the low- scaling
behavior of the total photoabsorption cross section as for
, and as for .
Here, denotes the low- scaling variable, with being
the saturation scale. The model-independent analysis also implies
at any for asymptotically
large energy, . Consistency with pQCD evolution determines the underlying
gluon distribution and the numerical value of in the expression
for the saturation scale, . In the
model-dependent analysis, by restricting the mass of the actively contributing
fluctuations by an energy-dependent upper bound, we extend the
validity of the color-dipole picture to . The
theoretical results agree with the world data on DIS for .Comment: 77 pages, 30 figure
Multiparton interactions and production of minijets in high energy hadronic collisions
We discuss the inclusive cross section to produce two minijets with a large
separation in rapidity in high energy hadronic collisions. The contribution to
the inclusive cross section from the exchange of a BFKL Pomeron is compared
with the contribution from the exchange of two BFKL Pomerons, which is induced
by the unitarization of the semi-hard interaction. The effect of the multiple
exchange is studied both as a function of the azimuthal correlation and as a
function of the transverse momentum of the observed minijets.Comment: TeX file, 20 pages, 4 figures available on reques
Virtual photon scattering at high energies as a probe of the short distance pomeron
Perturbative QCD predicts the behavior of scattering at high energies and
fixed (sufficiently large) transferred momenta in terms of the BFKL pomeron (or
short distance pomeron). We study the prospects for testing these predictions
in two-photon processes at LEP200 and a possible future e+ e- collider. We
argue that the total cross section for scattering two photons sufficiently far
off shell provides a clean probe of BFKL dynamics. The photons act as color
dipoles with small transverse size, so that the QCD interactions can be treated
perturbatively. We analyze the properties of the QCD result and the possibility
of testing them experimentally. We give an estimate of the rates expected and
discuss the uncertainties of these results associated with the accuracy of the
present theoretical calculations.Comment: 44 pages with 17 figures. REVTEX. Published version, with minor
changes from original submissio
Non-Linear Pomeron Trajectory in Diffractive Deep Inelastic Scattering
Recent experimental data on diffractive deep inelastic scattering collected
by the H1 and ZEUS Collaborations at HERA are analysed in a model with a
non-linear trajectory in the pomeron flux. The dependence of the
diffractive structure function is predicted. The normalization of
the pomeron flux and the (weak) dependence of the pomeron structure
function are revised as well.Comment: 16 pages, Latex + 3 figures, postscrip
Non-linear QCD dynamics in two-photon interactions at high energies
Perturbative QCD predicts that the growth of the gluon density at high
energies should saturate, forming a Color Glass Condensate (CGC), which is
described in mean field approximation by the Balitsky-Kovchegov (BK) equation.
In this paper we study the interactions at high energies and
estimate the main observables which will be probed at future linear colliders
using the color dipole picture. We discuss in detail the dipole - dipole cross
section and propose a new relation between this quantity and the dipole
scattering amplitude. The total ,
cross-sections and the real photon structure function are
calculated using the recent solution of the BK equation with running coupling
constant and the predictions are compared with those obtained using
phenomenological models for the dipole-dipole cross section and scattering
amplitude. We demonstrate that these models are able to describe the LEP data
at high energies, but predict a very different behavior for the observables at
higher energies. Therefore we conclude that the study of
interactions can be useful to constrain the QCD dynamics.Comment: 11 pages, 5 figures. Version to be published in European Physical
Journal
Rapidity gaps and production of minijets in high-energy hadronic collisions
High energy hadronic interactions can produce a final state characterized by
minijets separated by a large gap in the rapidity distribution of the produced
secondary particles. We discuss the process by keeping into account the
possibility of having multiple parton collisions in the hadronic interaction.
At Tevatron energy the correction to the single scattering term induced by the
presence of multiparton interactions is large for transverse momenta smaller
than 6 GeV.Comment: 29 pages, TeX file, 2 figures which are now include
HERA Collider Physics
HERA, the first electron-proton collider, has been delivering luminosity
since 1992. It is the natural extension of an impressive series of fixed-target
lepton-nucleon scattering experiments. The increase of a factor ten in
center-of-mass energy over that available for fixed-target experiments has
allowed the discovery of several important results, such as the large number of
slow partons in the proton, and the sizeable diffractive cross section at large
. Recent data point to a possible deviation from Standard Model
expectations at very high , highlighting the physics potential of HERA for
new effects. The HERA program is currently in a transition period. The first
six years of data taking have primarily elucidated the structure of the proton,
allowed detailed QCD studies and had a strong impact on the understanding of
QCD dynamics. The coming years will bring the era of electroweak studies and
high measurements. This is therefore an appropriate juncture at which to
review HERA results.Comment: 351 pages, 154 figures, submitted to Reviews of Modern Physic