35 research outputs found
Exclusive high- electroproduction: light-cone wave functions and electromagnetic form factors of mesons,
We apply the light-cone technique to electroproduction reaction long considered as a means of measuring the electromagnetic form
factor of the pion. We show that the interpretation of the long-standing puzzle
of large transverse cross section () in terms of the transition on the mesons in the light-cone proton is possible, but
requires quite a slow decrease of the F_{\rho\pi}(\q2) form factor. This
interpretation can be tested in the related reaction.
Corrections which are due to the final-state meson-baryon interactions (FSI)
are evaluated and are shown to amount to a effect at moderately large
\q2. Vanishing FSI with increasing - the color transparency phenomenon
- is shown to be very strong
The color dipole BFKL-Regge expansion: from DIS on protons to pions to rise of hadronic cross sections
As noticed by Fadin, Kuraev and Lipatov in 1975 incorporation of asymptotic
freedom into the BFKL equation splits the QCD pomeron into a series of isolated
poles in complex angular momentum plane. Following our earlier work on the
proton structure function we explore the phenomenological consequences of the
emerging BFKL-Regge factorized expansion for the small- structure function
of the pion . We calculate in a small- region
and find good agreement with the recent H1 determination of .
We also present the BFKL-Regge factorization based evaluation of the
contribution from hard scattering to the observed rise of the , and
real photo-absorption and total cross sections.Comment: 12 pages Latex 2 PS figures, Revised version accepted for publication
in Physics Letters
The spectrum and solutions of the generalized BFKL equation for total cross section
The colour dipole cross section is the principal quantity in the lightcone
-channel description of the diffractive scattering. Recently we have shown
that the dipole cross section satisfies the generalized BFKL equation. In this
paper we discuss properties and solutions of our generalized BFKL equation with
allowance for the finite gluon correlation radius . The latter is
introduced in a gauge invariant manner. We present estimates of the intercept
of the pomeron and find the asymptotic form of the dipole cross section.Comment: 18 pages, 3 figures upon request from
[email protected]
How open charm production and scaling violations probe the rightmost hard BFKL pole exchange
In 1994 Zakharov and the present authors argued that in color dipole (CD)
BFKL approach to DIS excitation of open charm at moderately large Q2 is
dominated by hard BFKL exchange. In view of the rapid accumulation of the
experimental data on small-x charm structure function of the proton F2cc from
HERA, we subject the issue of dominance of the rightmost hard BFKL pole
exchange to further scrutiny. Based on CD BFKL-Regge factorization we report
parameter-free predictions for the charm structure function F2cc and show that
the background to the dominant rightmost hard BFKL exchange from subleading
hard BFKL and soft-pomeron exchanges is negligible small from real
photo-production to DIS at Q2 lsim 50-100 GeV2. The agreement with the
experiment is good and lends strong support for the intercept of the rightmost
hard BFKL pole DeltaPom=alphaPom-1=0.4 as found in 1994 in the color dipole
approach. We comment on the related determination of DeltaPom from the
x-dependence of the longitudinal structure function FL(x,Q2) and of the scaling
violation dF2/dlog Q2 taken at a suitable value of Q2. \Comment: 16 pages, 7 figures; a discussion of thge longitudinal structure
function and scaling violations is adde
Exploratory study of shrinkage of the diffraction cone for the generalized BFKL pomeron
In color dipole gBFKL dynamics, we describe the emerging gBFKL phenomenology
of a subasymptotic energy dependence of the diffraction slope and discuss
possibilities of testing the gBFKL predictions in exclusive photo- and
electroproduction of vector mesons at HERA. A substantial shrinkage of the
diffraction cone processes from the CERN/FNAL to
HERA range of energy is predicted. This subasymptotic shrinkage is faster
than expected from the small slope of pomeron's Regge trajectory
\alpha_{\Pom}'. We point out that the diffraction slope is a scaling function
of , what relates production of different vector mesons.Comment: plain LaTeX, 4 figures upon the request from
[email protected]
Asymmetry of Strange Sea in Nucleons
Based on the finite-temperature field theory, we evaluate the medium effects
in nucleon which can induce an asymmetry between quarks and antiquarks of the
strange sea. The short-distance effects determined by the weak interaction can
give rise to where is the medium-induced mass of strange quark by a few KeV at
most, but the long-distance effects by strong interaction are sizable. Our
numerical results show that there exists an obvious mass difference between
strange and anti-strange quarks, as large as 10-100 MeV.Comment: 15 latex pages, 3 figures, to appear in PR
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.
The Onset of Color Transparency in Reactions on Nuclei
Quantum filtering of the ejectile wave packet from hard scattering on
bound nucleons puts stringent constraints on the onset of color transparency in
reactions in nuclei at moderate energies. Based on
multiple-scattering theory, we derive a novel formula for nuclear transparency
and discuss its energy dependence in terms of a color transparency sum rule.Comment: 14 pages (LATEX), 3 figures (not included, available from the
authors), KFA-IKP(TH)-1992-1
Deep Inelastic Scattering from off-Shell Nucleons
We derive the general structure of the hadronic tensor required to describe
deep-inelastic scattering from an off-shell nucleon within a covariant
formalism. Of the large number of possible off-shell structure functions we
find that only three contribute in the Bjorken limit. In our approach the usual
ambiguities encountered when discussing problems related to off-shellness in
deep-inelastic scattering are not present. The formulation therefore provides a
clear framework within which one can discuss the various approximations and
assumptions which have been used in earlier work. As examples, we investigate
scattering from the deuteron, nuclear matter and dressed nucleons. The results
of the full calculation are compared with those where various aspects of the
off-shell structure are neglected, as well as with those of the convolution
model.Comment: 36 pages RevTeX, 9 figures (available upon request), ADP-93-210/T128,
PSI-PR-93-13, accepted for publication in Physical Review
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