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 $c\bar{c}g$-production in diffractive DIS with finite quark masses at zero momentum transfer $t$. The calculation is done in the leading log(1/$x_{P}$) approximation and is valid in the region of high diffractive masses $M$ (small $\beta$). We apply our cross section formula including both $c{\bar c}$- and $c\bar{c}g$ in a Monte Carlo simulation to diffractive $D^{*\pm}$ 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