122 research outputs found
Gaps between Jets: Matching two Approaches
We calculate the parton level cross section for the production of two jets
that are far apart in rapidity, subject to a limitation on the total transverse
momentum Q_0 in the interjet region. We specifically address the question of
how to combine the approach which sums all leading logarithms in Q/Q_0 (where Q
is the jet transverse momentum) with the BFKL approach, in which leading
logarithms of the scattering energy are summed. Using an "all orders" matching,
we obtain results for the cross section which correctly reproduce the two
approaches in the appropriate limits.Comment: Talk given at 13th International Workshop on Deep Inelastic
Scattering (DIS 2005), Madison/Wisconsin, USA, April 27 - May 1, 200
The colour evolution of the process q q -> q q g
We calculate the soft anomalous dimension matrix for a five-parton process,
qq -> qqg. Considering different bases we unveil some interesting properties of
this matrix.Comment: 11 pages; calculation extended to general 5-parton kinematic
Massive c\bar c g - Calculation in Diffractive DIS and Diffractive D^* - Production at HERA
We calculate the cross section for -production in diffractive DIS
with finite quark masses at zero momentum transfer . The calculation is done
in the leading log(1/) approximation and is valid in the region of high
diffractive masses (small ). We apply our cross section formula
including both - and in a Monte Carlo simulation to
diffractive meson production at HERA. We compare our predictions to
results of H1 using three parameterizations for the unintegrated gluon density.Comment: 11 pages, 5 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
Color evolution of 2 -> 3 processes
The color structure needed for resummation of all colored 2 -> 3 processes is
calculated using multiplet inspired s-channel bases. In this way the resulting
matrices, describing the color structure, are guaranteed to obey simplifying
symmetries.Comment: 25 page
The Process \gamma^{*}_L+ q \to q\bar{q}g + q: Real Corrections to the Virtual Photon Impact Factor
We calculate, for the longitudinally polarized virtual photon, the cross
section of the process \gamma^{*}+q\to (q\bar{q}g)+q at high energies with a
large rapidity gap between the fragmentation system q\bar{q}g and the other
quark. This process provides the real corrections of the virtual photon impact
factor in the next-to leading order. Evidence is given for the appearance of a
new q\bar{q}g Fock-component of the photon state.Comment: 17 pages, 4 figures, revte
NLO Corrections to the \gamma* Impact Factor: First Numerical Results for the Real Corrections to \gamma*_L
We analytically perform the transverse momentum integrations in the real
corrections to the longitudinal \gamma*_L impact factor. The resulting
integrals are Feynman parameter integrals, and we provide a MATHEMATICA file
which contains the integrands. The remaining integrals are carried out
numerically. We perform a numerical test, and we compute those parts of the
impact factor which depend upon the energy scale s_0: they are found to be
negative and, with decreasing values of s_0, their absolute value increases.Comment: 27 pages, 5 figures, uses revtex4; misprint in fig.4,5 and typos
corrected; for associated files, see
http://www.desy.de/uni-th/smallx/kyrie/ImpFactor/index.htm
NLO corrections to the photon impact factor: Combining real and virtual corrections.
In this third part of our calculation of the QCD NLO corrections to the
photon impact factor we combine our previous results for the real corrections
with the singular pieces of the virtual corrections and present finite analytic
expressions for the quark-antiquark-gluon intermediate state inside the photon
impact factor. We begin with a list of the infrared singular pieces of the
virtual correction, obtained in the first step of our program. We then list the
complete results for the real corrections (longitudinal and transverse photon
polarization). In the next step we define, for the real corrections, the collinear
and soft singular regions and calculate their contributions to the impact factor.
We then subtract the contribution due to the central region. Finally, we
combine the real corrections with the singular pieces of the virtual corrections
and obtain our finite results
- …