Eric Laenen

Soft Gluon Radiation in Higgs Boson Production at the LHC

We examine the contributions of soft gluons to the Higgs production cross section at the LHC in the Standard Model and its minimal supersymmetric extension. The soft gluon radiation effects of this reaction share many features with the Drell-Yan process, but arise at lowest order from a purely gluonic initial state. We provide an extension of the conventional soft gluon resummation formalism to include a new class of contributions which we argue to be universal, and resum these and the usual Sudakov effects to all orders. The effect of these new terms is striking: only if they are included, does the expansion of the resummed cross section to next-to-leading order reproduce the exact result to within a few percent for the full range of Higgs boson masses. We use our resummed cross section to derive next-to-next-to-leading order results, and their scale dependence. Moreover, we demonstrate the importance of including the novel contributions in the resummed Drell-Yan process.

Sudakov factorization and resummation

We present a unified derivation of the resummation of Sudakov logarithms, directly from the factorization properties of cross sections in which they occur. We rederive in this manner the well-known exponentiation of leading and non-leading logarithmic enhancements near the edge of phase space for cross sections such as deeply inelastic scattering, which are induced by an electroweak hard scattering. The relevant factorization theorems are known to hold for many such cross sections of interest, and we conjecture that they apply even more widely. For QCD hard-scattering processes, such as heavy-quark production, we show that the resummation of non-leading logarithms requires in general mixing in the space of the color tensors of the hard scattering. The exponentiation of Sudakov logarithms implies that many weighted cross sections obey particular evolution equations in momentum transfer, which streamline the computation of their Sudakov exponents. We illustrate this method with the resummation of soft-gluon enhancements of the inclusive Drell-Yan cross section, in both DIS and MS factorization schemes.

QCD corrections to W boson plus heavy quark production at the Tevatron

Abstract The next-to-leading order QCD correction to the production of a W boson in association with a jet containing a heavy quark are presented. The calculation is fully differential in the final state particle momenta and includes the mass of the heavy quark. We study for the case of the Tevatron the sensitivity of the cross section to the strange quark distribution function, the dependence of the cross section on the heavy quark mass, the transverse momentum distribution of the jet containing the heavy quark, and the momentum distribution of the heavy quark in the jet.

A new evolution equation

We propose a new evolution equation for the gluon density relevant for the region of small xB. It generalizes the GLR equation and allows deeper penetration in dense parton systems than the GLR equation does. This generalization consists of taking shadowing effects more comprehensively into account by including multigluon correlations, and allowing for an arbitrary initial gluon distribution in a hadron. We solve the new equation for fixed αs. We find that the effects of multigluon correlations on the deep-inelastic structure function are small.

Soft gluon resummation for squark and gluino pair-production at hadron colliders

RADCOR 2009 - 9th International Symposium on Radiative Corrections (Applications of Quantum Field Theory to Phenomenology), 25 oktober 2009

W plus heavy quark production at the Tevatron

We present the next-to-leading order QCD corrections to the production of a

Heavy-quark production in eγ scattering

W

Heavy-quark correlations in direct photon-photon collisions

-boson in association with a jet containing a heavy quark. The calculation is fully differential in the final state particle momenta and includes the mass of the heavy quark. We study for the case of the Tevatron the sensitivity of the cross section to the strange quark distribution function, the dependence of the cross section on the heavy quark mass, the transverse momentum distribution of the jet containing the heavy quark, and the momentum distribution of the heavy quark in the jet.

Radiative corrections to eγ scattering

Abstract Open heavy flavour production at e + e − colliders in deeply inelastic eγ scattering has an interesting feature: the structure function F 2 ( x , Q 2 ) for this process is calculable for x > 0.01, and is essentially proportional to the gluon density in the photon for smaller x values. We give estimates for event rates at LEP2 and a Next Linear Collider in x , Q 2 bins, and present differential distributions in the transverse momentum and rapidity of the heavy quark for the case of charm. We include all next-to-leading-order QCD corrections, and find theoretical uncertainties are well under control.

Higher order QCD corrections to tagged production processes

Abstract In two-photon collisions at LEP2 and a future e + e − linear collider heavy quarks (mainly charm) will be pair-produced rather copiously. The production via direct and resolved photons can be distinguished experimentally via a remnant-jet tag. We study correlations of the heavy quarks at next-to-leading order in QCD in the direct channel, which is free from phenomenological parton densities in the photon. These correlations are therefore directly calculable in perturbative QCD and provide a stringent test of the production mechanism.