440 research outputs found
Observing the Odderon: Tensor Meson Photoproduction
We calculate high-energy photoproduction of the tensor meson by
odderon and photon exchange in the reaction , where X is either the nucleon or the sum of the N(1520) and N(1535)
baryon resonances. Odderon exchange dominates except at very small transverse
momentum, and we find a cross section of about 20 nb at a centre-of-mass energy
of 20 GeV. This result is compared with what is currently known experimentally
about photoproduction. We conclude that odderon exchange is not ruled out
by present data. On the contrary, an odderon-induced cross section of the above
magnitude may help to explain a puzzling result observed by the E687
experiment.Comment: 19 pages, 11 figure
The colour dipole approach to small-x processes
We explain why it is possible to formulate a wide variety of high energy
(small-x) photon-proton processes in terms of a universal dipole cross section
and compare and contrast various parameterizations of this function that exist
in the literature.Comment: 6 pages, latex, 2 figures. Contribution to Durham Collider Workshop
(Sept 99) proceeding
Klein Tunnelling and the Klein Paradox
The Klein paradox is reassessed by considering the properties of a finite
square well or barrier in the Dirac equation. It is shown that spontaneous
positron emission occurs for a well if the potential is strong enough. The
vacuum charge and lifetime of the well are estimated. If the well is wide
enough, a seemingly constant current is emitted. These phenomena are transient
whereas the tunnelling first calculated by Klein is time-independent. Klein
tunnelling is a property of relativistic wave equations, not necessarily
connected to particle emission. The Coulomb potential is investigated in this
context: it is shown that a heavy nucleus of sufficiently large will bind
positrons. Correspondingly, it is expected that as increases the Coulomb
barrier will become increasingly transparent to positrons. This is an example
of Klein tunnelling.Comment: 17 page
Eikonal profile functions and amplitudes for and scattering
The eikonal profile function obtained from the Model of the Stochastic
Vacuum is parametrized in a form suitable for comparison with experiment. The
amplitude and the extended profile function (including imaginary and real
parts) are determined directly from the complete pp and p elastic
scattering data at high energies. Full and accurate representation of the data
is presented, with smooth energy dependence of all parameters. The changes
needed in the original profile function required for description of scattering
beyond the forward direction are described.Comment: Latex, 28 pages and 16 figure
Baryons in the Field Correlator Method: Effects of the Running Strong Coupling
The ground and P-wave excited states of nnn, nns and ssn baryons are studied
in the framework of the Field Correlator Method using the running strong
coupling constant in the Coulomb-like part of the three-quark potential. The
running coupling is calculated up to two loops in the background perturbation
theory. The three-quark problem has been solved using the hyperspherical
functions method. The masses of the S- and P-wave baryons are presented. Our
approach reproduces and improves the previous results for the baryon masses
obtained for the freezing value of the coupling constant. The string correction
for the confinement potential of the orbitally excited baryons, which is the
leading contribution of the proper inertia of the rotating strings, is
estimated.Comment: 13 pages, 1 figure, 5 table
Heisenberg's Universal (lns)**2 Increase of Total Cross Sections
The (lns)**2 behaviour of total cross-sections, first obtained by Heisenberg
50 years ago, receives now increased interest both on phenomenological and
theoretical levels. In this paper we present a modification of the Heisenberg's
model in connection with the presence of glueballs and we show that it leads to
a realistic description of all existing hadron total cross-section data.Comment: 6 pages, 3 figure
Energy Losses (Gains) of Massive Coloured Particles in Stochastic Colour Medium
The propagation of massive coloured particles in stochastic background
chromoelectric field is studied using the semiclassical equations of motion.
Depending on the nature of the stochastic background we obtain the formulae for
the energy losses of heavy coloured projectile in nonperturbative hadronic
medium and for the energy gains in the stochastic field present, e.g., in the
turbulent plasma. The result appears to be significantly dependent on the form
of the correlation function of stochastic external fieldComment: 9 pages, BI-TP 94/15, plain LaTe
From the Feynman-Schwinger representation to the non-perturbative relativistic bound state interaction
We write the 4-point Green function in QCD in the Feynman-Schwinger
representation and show that all the dynamical information are contained in the
Wilson loop average. We work out the QED case in order to obtain the usual
Bethe-Salpeter kernel. Finally we discuss the QCD case in the non-perturbative
regime giving some insight in the nature of the interaction kernel.Comment: 25 pages, RevTex, 3 figures included, typos corrected, to appear in
Phys. Rev. D 5
Triangular and Y-shaped hadrons in QCD
Gauge invariant extended configurations are considered for the three
fundamental (quarks) or adjoint (gluons) particles. For quarks it is shown that
the Y-shaped configuration is the only possible. For adjoint sources both the
Y-shaped and triangular configurations may realize. The corresponding static
potentials are calculated in the Method of Field Correlators and in the case of
baryon shown to be consistent with the lattice simulations. For adjoint sources
the potentials of Y-shaped and Delta-shaped configurations turn out to be close
to each other, which leads to almost degenerate masses of 3-- 3g glueballs and
odderon trajectories.Comment: 9 pages, 5 eps figures, latex2e, one reference adde
- …