293 research outputs found
Production of two pairs in gluon-gluon scattering in high energy proton-proton collisions
We calculate cross sections for in the
high-energy approximation in the mixed (longitudinal momentum fraction, impact
parameter) and momentum space representations. Besides the total cross section
as a function of subsystem energy also differential distributions (in quark
rapidity, transverse momentum, , invariant mass) are presented.
The elementary cross section is used to calculate production of in single-parton scattering (SPS) in proton-proton collisions. We
present integrated cross section as a function of proton-proton center of mass
energy as well as differential distribution in . The
results are compared with corresponding results for double-parton scattering
(DPS) discussed recently in the literature. We find that the considered SPS
contribution to production is at high energy ( 5 TeV) much smaller than that for DPS contribution.Comment: 17 pages, 11 figure
Production of Z^0 bosons with rapidity gaps: exclusive photoproduction in gamma p and p p collisions and inclusive double diffractive Z^0's
We extend the k_\perp-factorization formalism for exclusive photoproduction
of vector mesons to the production of electroweak Z^0 bosons. Predictions for
the gamma p \to Z^0 p and p p \to p p Z^0 reactions are given using an
unintegrated gluon distribution tested against deep inelastic data. We present
distributions in the Z^0 rapidity, transverse momentum of Z^0 as well as in
relative azimuthal angle between outgoing protons. The contributions of
different flavours are discussed. Absorption effects lower the cross section by
a factor of 1.5-2, depending on the Z-boson rapidity. We also discuss the
production of Z^0 bosons in central inclusive production. Here rapidity and
(x_{\Pom,1}, x_{\Pom,2}) distributions of Z^0 are calculated. The corresponding
cross section is about three orders of magnitude larger than that for the
purely exclusive process.Comment: 19 pages, 14 figs, A. Cisek is married name of A. Rybarsk
Exclusive photoproduction of meson in and reactions
The amplitude for is calculated in a pQCD -
factorization approach. The total cross section for this process is compared
with HERA data. Total cross section, as a function of photon-proton energy and
photon virtuality, is calculated. We also discuss the ratio of /
and the dependence on the mass of the strange quark. The amplitude
for is used to predict the cross section for exclusive
photoproduction of meson in proton-proton collisions. Absorption effects
are included. The results for RHIC, Tevatron and LHC energies are presented.Comment: 10 pages, 5 figure
Testing the Meson Cloud Model in Inclusive Meson Production
We have applied the Meson Cloud Model to calculate inclusive momentum spectra
of pions and kaons produced in high energy proton-proton and proton-nucleus
collisions. For the first time these data are used to constrain the cloud
cut-off parameters. We show that it is possible to obtain a reasonable
description of data, especially the large () part of the
spectrum and at the same time describe (partially) the E866 data on and . We also discuss the relative strength of the
and vertices. We find out that the corresponding cut-off
parameters should be both soft and should not differ by more than 200 MeV from
each other. An additional source (other than the meson cloud) of sea antiquark
asymmetry, seems to be necessary to completely explain the data. A first
extension of the MCM to proton nucleus collisions is discussed.Comment: 14 pages, Latex, 6 ps figures. Submitted to Phys. Rev.
Pion Content of the Nucleon as seen in the NA51 Drell-Yan experiment
In a recent CERN Drell-Yan experiment the NA51 group found a strong asymmetry
of and densities in the proton at . We interpret
this result as a decisive confirmation of the pion-induced sea in the nucleon.Comment: 10 pages + 3 figures, Preprint KFA-IKP(TH)-1994-14 .tex file. After
\enddocument a uu-encodeded Postscript file comprising the figures is
appende
Prediction for unintegrated parton distributions
Unintegrated parton distributions in the proton and nucleus are predicted by
a modified DGLAP equation incorporating the shadowing corrections, which
include exact energy-momentum conservation in each splitting and fusion
vertices. We find that the nuclear shadowing effects are obvious, although they
are far from the saturation limit. On the other hand, we point out that the
suppression of the unintegrated gluon distribution toward lower may
arise from the valence-like input rather than the saturation effects.Comment: Review article, 50 pages, 19 figures. To appear in Physical Review
Particle multiplicities at LHC and deviations from limiting fragmentation
The pseudorapidity density of charged particles produced at LHC collisions
are predicted by using two complementary production mechanisms with a set of
consistent integrated and unintegrated parton distributions. We discuss the
limiting fragmentation hypothesis and its possible violation, and we compare
our model with other partonic models.Comment: 26 pages, 27 figures, Accepted for publication in Phys. Rev.
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