An algorithm to automatically compute any one-loop amplitude for all momentum, color, and helicity configurations of the external particles is presented. It has been implemented using the tools HELAC for the evaluation of tree-level off-shell currents, CutTools for OPP-reduction and OneLOop for the evaluation of one-loop scalar integrals. It proves to be able to deal with at least all sub-processes included in the 2007 Les Houches wish list for LHC involving 3 or 4 particles in the final state.

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We propose a novel way of studying the gluon number density (the so-called Weizsäcker–Williams gluon distribution) using the planned Electron Ion Collider. Namely, with the help of the azimuthal correlations between the total transverse momentum of the dijet system and the scattered electron, we examine an interplay between the effect of the soft gluon emissions (the Sudakov form factor) and the gluon saturation effects. The kinematic cuts are chosen such that the dijet system is produced in the forward direction in the laboratory frame, which provides an upper bound on the probed longitudinal fractions of the hadron momentum carried by scattered gluons. Further cuts enable us to use the factorization formalism that directly involves the unpolarized Weizsäcker–Williams gluon distribution. We find this observable to be very sensitive to the soft gluon emission and moderately sensitive to the gluon saturation.

A common library, TMDlib2, for Transverse-Momentum-Dependent distributions (TMDs) and unintegrated parton distributions (uPDFs) is described, which allows for easy access of commonly used TMDs and uPDFs, providing a three-dimensional (3D) picture of the partonic structure of hadrons. The tool TMDplotter allows for web-based plotting of distributions implemented in TMDlib2, together with collinear pdfs as available in LHAPDF.

We present a prescription to construct manifestly gauge invariant tree-level helicity amplitudes with one or two off-shell initial-state partons, and arbitrary particles in the final state. Such amplitudes are needed in calculations within high-energy factorization schemes, in which the initialstate partons have non-vanishing transverse momentum components. The prescription allows for efficient calculations that are easy to automate, and leads to results that are equivalent to those obtained with the well-known effective action approach.