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

Predicting F2D(3) from the dipole cross-section

We employ a parameterisation of the proton dipole cross section previously extracted from electroproduction and photoproduction data to predict the diffractive structure function F2D(3)(Q^2, beta, xpom). Comparison with HERA H1 data yields good agreement.Comment: 5 pages,4 figures, Latex2e, uses espcrc1.sty. Presented at "Hadron 99" Beijing, August 1999. Reference added, erroneous citation correcte

QCD coherence and jet rates in small x deep inelastic scattering

The contributions to the deep inelastic scattering structure function which arise from emission of zero, one, two or three resolvable gluons and any number of unresolvable ones are computed to order ${\bar \alpha}_{S}^{3}$. Coherence effects are taken into account via angular ordering and are demonstrated to yield (at the leading logarithm level) the identical results to those obtained assuming the multi-Regge kinematics of BFKL.Comment: 14 pages. Extensively rewritten. To be published in Physics Letters

Soft gluons and superleading logarithms in QCD

After a brief introduction to the physics of soft gluons in QCD we present a surprising prediction. Dijet production in hadron-hadron collisions provides the paradigm, i.e. h_1 +h_2 \to jj+X. In particular, we look at the case where there is a restriction placed on the emission of any further jets in the region in between the primary (highest p_T) dijets. Logarithms in the ratio of the jet scale to the veto scale can be summed to all orders in the strong coupling. Surprisingly, factorization of collinear emissions fails at scales above the veto scale and triggers the appearance of double logarithms in the hard sub-process. The effect appears first at fourth order relative to the leading order prediction and is subleading in the number of colours.Comment: Talk presented at the workshop "New Trends in HERA Physics", Ringberg Castle, Tegernsee, 5-10 October 200

Quantum Chromodynamics and the Pomeron

This volume describes the Pomeron, an object of crucial importance in very high energy particle physics. Starting with a general description of the Pomeron within the framework of Regge theory, the emergence of the Pomeron within scalar field theory is discussed, providing a natural foundation on which to develop the more realistic case of QCD. The reggeization of the gluon is demonstrated and used to build the Pomeron of perturbative QCD. The dynamical nature of the Pomeron and its role in small-x deep inelastic scattering and in diffractive scattering is also examined in detail. The volume concludes with a study of the colour dipole approach to high energy scattering and the explicit role of unitarity corrections. This book will be of interest to theoretical and experimental particle physicists, and applied mathematicians. First published in 1997, this title has been reissued as an Open Access publication

Symmetry of Anomalous Dimension Matrices for Colour Evolution of Hard Scattering Processes

In a recent paper, Dokshitzer and Marchesini rederived the anomalous dimension matrix for colour evolution of $gg \to gg$ scattering, first derived by Kidonakis, Oderda and Sterman. They noted a weird symmetry that it possesses under interchange of internal (colour group) and external (scattering angle) degrees of freedom and speculated that this may be related to an embedding into a context that correlates internal and external variables such as string theory. In this short note, I point out another symmetry possessed by all the colour evolution anomalous dimension matrices calculated to date. It is more prosaic, but equally unexpected, and may also point to the fact that colour evolution might be understood in some deeper theoretical framework. To my knowledge it has not been pointed out elsewhere, or anticipated by any of the authors calculating these matrices. It is simply that, in a suitably chosen colour basis, they are complex symmetric matrices.Comment: 3 page

Solving the BFKL Equation with Running Coupling

We describe a formalism for solving the BFKL equation with a coupling that runs for momenta above a certain infrared cutoff. By suitably choosing matching conditions proper account is taken of the fact that the BFKL diffusion implies that the solution in the infrared (fixed coupling) regime depends upon the solution in the ultraviolet (running coupling) regime and vice versa. Expanding the BFKL kernel to a given order in the ratio of the transverse momenta allows arbitrary accuracy to be achieved.Comment: 11 pages, 2 fig

Diffractive upsilon production at the LHC

We compute the rate for diffractive upsilon meson production at the Tevatron and the LHC. The upsilon is produced diffractively via the subprocess gamma + p -> upsilon + p where the initial photon is radiated off an incoming proton (or antiproton). We consider the possibility to use low angle proton detectors to make a measurement of the gamma p cross-section and conclude that a measurement of the cross-section at a centre of mass energy in excess of 1 TeV is possible at the LHC. This is in the region where saturation effects are likely to reveal themselves.Comment: 14 page

WW scattering at the CERN LHC

A detailed study is presented of elastic WW scattering in the scenario that there are no new particles discovered prior to the commissioning of the CERN LHC. We work within the framework of the electroweak chiral Lagrangian and two different unitarization protocols are investigated. Signals and backgrounds are simulated to the final-state-particle level. A new technique for identifying the hadronically decaying W is developed, which is more generally applicable to massive particles which decay to jets where the separation of the jets is small. The effect of different assumptions about the underlying event is also studied. We conclude that the channel WW-->jj+lν may contain scalar and/or vector resonances which could be measurable after 100 fb-1 of LHC data

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