813 research outputs found
Large multiplicity fluctuations and saturation effects in onium collisions
This paper studies two related questions in high energy onium-onium
scattering: the probability of producing an unusually large number of particles
in a collision, where it is found that the cross section for producing a
central multiplicity proportional to should decrease exponentially in
. Secondly, the nature of gluon (dipole) evolution when dipole
densities become so high that saturation effects due to dipole-dipole
interactions become important: measures of saturation are developed to help
understand when saturation becomes important, and further information is
obtained by exploiting changes of frame, which interchange unitarity and
saturation corrections.Comment: 30 pages LaTeX2e, 11 figures included using epsfig. Compressed
postscript of whole paper also available at
http://www.hep.phy.cam.ac.uk/theory/papers
OEDIPUS: Onium Evolution, Dipole Interaction and Perturbative Unitarisation Simulation
A Monte Carlo simulation program is presented which can be used to determine
the small- evolution of a heavy onium using Mueller's colour dipole
formulation, giving the full distribution of dipoles in rapidity and impact
parameter. Routines are also provided which calculate onium-onium scattering
amplitudes between individual pairs of onium configurations, making it possible
to establish the contribution of multiple pomeron exchange terms to onium-onium
scattering (the unitarisation corrections).Comment: 21 pages LaTeX2e. Postscript available from
http://www.hep.phy.cam.ac.uk/theory/papers and program available from
ftp://axpf.hep.phy.cam.ac.uk/pub/theory/oedipus.tar.g
A New Odderon Solution in Perturbative QCD
We present and discuss a new bound state solution of the three gluon system
in perturbative QCD. It carries the quantum numbers of the odderon, has
intercept at one and couples to the impact factor .Comment: 11 pages, latex, 1 figur
Small x evolution: BFKL vs Dipole Picture
The relation between the two approaches is discussed both in the linear and
nonlinear regimes. It is connected to the gauge invariance and Moebius symmetry
in LL perturbative QCD. First corrections beyond the large N approximation are
discussed for the nonlinear case.Comment: 4 pages, 1 figure; Proceedings of Diffraction 2004, 13-18 september
2004, Cala Gonone, Sardinia, Ital
Studies of Unitarity at Small~ Using the Dipole Formulation
Mueller's dipole formulation of onium-onium scattering is used to study
unitarity corrections to the BFKL power growth at high energies. After a short
discussion of the spatial distribution of colour dipoles in a heavy quarkonium
and the associated fluctuations, results are presented showing that the one and
two-pomeron contributions to the total cross section are the same at a rapidity
. Above this rapidity the large fluctuations in the onium wave
function cause the multiple pomeron series to diverge. Resumming the series
allows one to show that unitarity corrections set in gradually for the total
cross section, which is dominated by rare, large, configurations of the onia.
The elastic cross section comes mostly from much smaller impact parameters and
has significant unitarity corrections starting at a rapidity .Comment: 30 pages LaTeX2e with 12 figures as appended as uuencoded eps. Uses
epsfig. Postscript file for complete paper available from
http://www.hep.phy.cam.ac.uk/theory/papers/index.htm
Multiplicity distribution of colour dipoles at small~
The colour dipole multiplicity distribution is analysed for the wave function
of a heavy onium state at small . Numerical results for the average
multiplicity and the effect of cutoffs on its power growth are presented. Then,
the full multiplicity distribution is analysed: the second multiplicity moment
is derived and the tail of the distribution is shown to behave as . These results are confirmed by a Monte Carlo simulation which also gives
the fluctuations in the spatial density of dipoles.Comment: submitted as uuencoded postscript file of whole paper: 14 pages with
5 figures. Postscript also available from
http://www.hep.phy.cam.ac.uk/theory/papers/index.htm
Nonlinear QCD Evolution: Saturation without Unitarization
We consider the perturbative description of saturation based on the nonlinear
QCD evolution equation of Balitsky and Kovchegov (BK). Although the nonlinear
corrections lead to saturation of the scattering amplitude locally in impact
parameter space, we show that they do not unitarize the total cross section.
The total cross section for the scattering of a strongly interacting probe on a
hadronic target is found to grow exponentially with rapidity. The origin of
this violation of unitarity is the presence of long range Coulomb fields away
from the saturation region. The growth of these fields with rapidity is not
tempered by the nonlinearity of the BK equation.Comment: 4 pages, RevTe
Deformed Spectral Representation of the BFKL Kernel and the Bootstrap for Gluon Reggeization
We investigate the space of functions in which the BFKL kernel acts. For the
amplitudes which describe the scattering of colorless projectiles it is
convenient to define, in transverse coordinates, the Moebius space in which the
solutions to the BFKL equation vanish as the coordinates of the two reggeized
gluons coincide. However, in order to fulfill the bootstrap relation for the
BFKL kernel it is necessary to modify the space of functions. We define and
investigate a new space of functions and show explicitly that the bootstrap
relation is valid for the corresponding spectral form of the kernel. We
calculate the generators of the resulting deformed representation of the
sl(2,C) algebra.Comment: 22 pages, 1 figur
Scaling Rule for Nonperturbative Radiation in a Class of Event Shapes
We discuss nonperturbative radiation for a recently introduced class of
infrared safe event shape weights, which describe the narrow-jet limit.
Starting from next-to-leading logarithmic (NLL) resummation, we derive an
approximate scaling rule that relates the nonperturbative shape functions for
these weights to the shape function for the thrust. We argue that the scaling
reflects the boost invariance implicit in NLL resummation, and discuss its
limitations. In the absence of data analysis for the new event shapes, we
compare these predictions to the output of the event generator PYTHIA.Comment: 23 pages, 3 figures, uses JHEP3.cls (included); v2 - version to
appear in JHE
Energy flow in QCD and event shape functions
Hadronization corrections to the thrust and related event shape distributions
in the two-jet kinematical region of e+e- annihilation are summarized by
nonperturbative shape functions. The moments of shape functions are given by
universal matrix elements in QCD, which describe the energy flow in QCD final
states. We show how the nonperturbative structure of these matrix elements may
be inferred from resummed perturbation theory and Lorentz invariance. This
analysis suggests the same functional forms for the shape functions as were
found in phenomenological studies, and sheds light on the physical significance
of the parameters that characterize these functions.Comment: 15 pages, LaTeX, 2 figure
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