1,362 research outputs found
Low x saturation at HERA ?
We compare the predictions of two distinct dipole models for inclusive and
exclusive diffractive processes. While only one of these dipole models contains
perturbative saturation dynamics, we show that the predictions of both models
are fully consistent with the available HERA data, indicating no compelling
evidence for saturation at present HERA energies.Comment: 8 pages, 4 figures, presented at the 26th
Montreal-Rochester-Syracuse-Toronto (MRST) conference held at Concordia
University, Montreal, Canada, 12th-14th May 2004. To appear in the
proceeding
THE STRUCTURE FUNCTION F_2^{\gamma}(x,Q^2) AT LEP2
The unique nature of the photon can be investigated in hitherto unexplored
kinematic regions at LEP2. We discuss the theoretical significance of deep
inelastic measurements and present a prescription that allows a theoretically
and experimentally sensible separation of the so-called `anomalous' and
`hadronic' components of the target photon. We perform preliminary studies
regarding the ability to reconstruct the CM energy (and hence
) and the usefulness of the easier to measure electron structure function.Comment: 6 pages Latex + 5 figures in a uuencoded fil
Super-leading logarithms in non-global observables in QCD: Fixed order calculation
Super-leading logarithmic terms have previously been observed in non-global
QCD observables. In this paper we re-calculate the first super-leading
contribution to the `gaps between jets' cross-section using a diagrammatic
fixed order approach. We calculate for the first time the super-leading
contribution at fifth order in alpha_s.Comment: 18 pages, 7 figure
Breakdown of QCD coherence ?
We reconsider the calculation of a non-global QCD observable and find the
possible breakdown of QCD coherence. This breakdown arises as a result of wide
angle soft gluon emission developing a sensitivity to emission at small angles
and it leads to the appearance of super-leading logarithms. We use the `gaps
between jets' cross-section as a concrete example and illustrate that the new
logarithms are intimately connected with the presence of Coulomb gluon
contributions. Numerical estimates of their potential phenomenological
significance are presented.Comment: 7 pages, 3 figures; proceedings of Workshop on Diffraction in
High-Energy Physics - DIFFRACTION 2006, Sep. 5-10 2006, Adamantas, Milos
island, Greec
Multiparton Interactions in Photoproduction at HERA
The high energy photoproduction of jets is being observed at the ep collider,
HERA. It may be that the HERA centre-of-mass energy is sufficiently large that
the production of more than one pair of jets per ep collision becomes possible,
owing to the large number density of the probed gluons. We construct a Monte
Carlo model of such multiparton interactions and study their effects on a wide
range of physical observables. The conclusion is that multiple interactions
could have very significant effects upon the photoproduction final state and
that this would for example make extractions of the gluon density in the photon
rather difficult. Total rates for the production of many (i.e. > 2) jets could
provide direct evidence for the presence of multiple interactions, although
parton showering and hadronization significantly affect low transverse energy
jets.Comment: 21 pages, 8 figures include
On the breaking of collinear factorization in QCD
We investigate the breakdown of collinear factorization for non-inclusive
observables in hadron-hadron collisions. For pure QCD processes, factorization
is violated at the three-loop level and it has a structure identical to that
encountered previously in the case of super-leading logarithms. In particular,
it is driven by the non-commutation of Coulomb/Glauber gluon exchanges with
other soft exchanges. Beyond QCD, factorization may be violated at the two-loop
level provided that the hard subprocess contains matrix element contributions
with phase differences between different colour topologies.Comment: Version 2: minor improvements for journal publicatio
The self-care for people initiative: the outcome evaluation.
To determine the effects of a community-based training programme in self-care on the lay population
Scattering of shock waves in QCD
The cross section of heavy-ion collisions is represented as a double
functional integral with the saddle point being the classical solution of the
Yang-Mills equations with boundary conditions/sources in the form of two shock
waves corresponding to the two colliding ions. I develop the expansion of this
classical solution in powers of the commutator of the Wilson lines describing
the colliding particles and calculate the first two terms of the expansion.Comment: 23 pages, 13 figure
Extracting the rho meson wavefunction from HERA data
We extract the light-cone wavefunctions of the rho meson using the HERA data
on diffractive rho photoproduction. We find good agreement with predictions for
the distribution amplitude based on QCD sum rules and from the lattice. We also
find that the data prefer a transverse wavefunction with enhanced end-point
contributions.Comment: 13 pages, 7 figures, significant improvements over the original
version with a new section on distribution amplitudes adde
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