303 research outputs found
Parametrisation of F_2^gamma at low Q^2 and of sigma(gamma,gamma) and sigma(gamma^*,gamma) at high energies
A parametrisation of the real photon structure function F_2^gamma in the low
Q^2, low x region is formulated. It includes both the VMD and the QCD
components, the latter suitably extrapolated to the low Q^2 region and based on
arbitrary parton distributions in the photon. The parametrisation used together
with the GRV and GRS' parton densities describes reasonably well the existing
high energy data on F_2^gamma, sigma(gamma,gamma) and the low Q^2 data on
sigma(gamma^*, gamma). Predictions for sigma(gamma,gamma) and for sigma(gamma^*
,gamma) for energies which may become accessible in future linear colliders are
also given.Comment: 21 pages, 11 figure
Spin dependent structure function at small and small
Theoretical expectations concerning the low and low behaviour of
are summarized and compared with the recent SMC data.Comment: 4 pages, plain LATEX, 1 eps figure; contribution to 3rd UK
Phenomenology Workshop on HERA Physics, St. John's College, Durham, UK,
September 199
Comment on the recent COMPASS data on the spin structure function g_1
We examine the recent COMPASS data on the spin structure function g_1
singlet. We show that it is rather difficult to use the data in the present
form in order to draw conclusions on the initial parton densities. However, our
tentative estimate is that the data better agree with positive rather than
negative initial gluon densities.Comment: 8 pages, 1 figur
Accessing the Longitudinally Polarized Photon Content of the Proton
We investigate the QED Compton process (QEDCS) in longitudinally polarized
lepton-proton scattering both in the elastic and inelastic channels and show
that the cross section can be expressed in terms of the polarized equivalent
photon distribution of the proton. We provide the necessary kinematical
constraints to extract the polarized photon content of the proton using this
process at HERMES, COMPASS and eRHIC. We also discuss the suppression of the
major background process coming from virtual Compton scattering. We point out
that such an experiment can give valuable information on in the
small , broad region at the future polarized collider eRHIC and
especially in the lower , medium region in fixed target experiments.Comment: Version to appear in PR
A polarized version of the CCFM equation for gluons
A derivation for a polarized CCFM evolution equation which is suitable to
describe the scaling behavior of the the unintegrated polarized gluon density
is given. We discuss the properties of this polarized CCFM equation and compare
it to the standard CCFM equation in the unpolarized case.Comment: 15 pages, 6 figures, RevTeX, some minor typos corrected, version to
appear in Phys. Rev.
High Energy Quark-Antiquark Elastic scattering with Mesonic Exchange
We studies the high energy elastic scattering of quark anti-quark with an
exchange of a mesonic state in the channel with .
Both the normalization factor and the Regge trajectory can be calculated in
PQCD in cases of fixed (non-running) and running coupling constant. The
dependence of the Regge trajectory on the coupling constant is highly
non-linear and the trajectory is of order of in the interesting physical
range.Comment: 29 page
Propagation of Muons and Taus at High Energies
The photonuclear contribution to charged lepton energy loss has been
re-evaluated taking into account HERA results on real and virtual photon
interactions with nucleons. With large processes incorporated, the
average muon range in rock for muon energies of GeV is reduced by only
5% as compared with the standard treatment. We have calculated the tau energy
loss for energies up to GeV taking into consideration the decay of the
tau. A Monte Carlo evaluation of tau survival probability and range show that
at energies below GeV, depending on the material, only tau decays
are important. At higher energies the tau energy losses are significant,
reducing the survival probability of the tau. We show that the average range
for tau is shorter than its decay length and reduce to 17 km in water for an
incident tau energy of GeV, as compared with its decay length of 49 km
at that energy. In iron, the average tau range is 4.7 km for the same incident
energy.Comment: 25 pages including 8 figure
Saturation Effects in Deep Inelastic Scattering at low and its Implications on Diffraction
We present a model based on the concept of saturation for small and
small . With only three parameters we achieve a good description of all Deep
Inelastic Scattering data below . This includes a consistent treatment
of charm and a successful extrapolation into the photoproduction regime. The
same model leads to a roughly constant ratio of diffractive and inclusive cross
section.Comment: 24 pages, 12 figures, Latex-fil
Diffractive Phenomena and Shadowing in Deep-Inelastic Scattering
Shadowing effects in deep-inelastic lepton-nucleus scattering probe the mass
spectrum of diffractive leptoproduction from individual nucleons. We explore
this relationship using current experimental information on both processes. In
recent data from the NMC and E665 collaboration, taken at small x << 0.1 and
Q^2 < 1 GeV^2, shadowing is dominated by the diffractive excitation and
coherent interaction of low mass vector mesons. If shadowing is explored at
small x > 1 GeV^2 as discussed at HERA, the situation is
different. Here dominant contributions come from the coherent interaction of
diffractively produced heavy mass states. Furthermore we observe that the
energy dependence of shadowing is directly related to the mass dependence of
the diffractive production cross section for free nucleon targets.Comment: 12 pages Latex, 8 figure
Phenomenological description of the gamma* p cross section at low Q2
Low Q2 photon-proton cross sections are analysed using a simple,
QCD-motivated parametrisation ,
which gives a good description of the data. The Q2 dependence of the gamma* p
cross section is discussed in terms of the partonic transverse momenta of the
hadronic state the photon fluctuates into.Comment: 14 pages, revtex, epsfig, 2 figure
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