Angular ordering and parton showers for non-global QCD observables

We study the mismatch between a full calculation of non-global single-logarithms in the large-N_c limit and an approximation based on free azimuthal averaging, and the consequent angular-ordered pattern of soft gluon radiation in QCD. We compare the results obtained in either case to those obtained from the parton showers in the Monte Carlo event generators HERWIG and PYTHIA, with the aim of assessing the accuracy of the parton showers with regard to such observables where angular ordering is merely an approximation even at leading-logarithmic accuracy and which are commonly employed for the tuning of event generators to data.Comment: 20 pages, 8 figure

Jet-veto efficiencies at all orders in QCD

We present a next-to-leading logarithmic resummation for the jet-veto efficiency in Higgs production. We then discuss how this prediction affects the theoretical uncertainties in the region of transverse momenta of interest for Higgs searches at the LHC.Comment: 5 pages, 2 figures. To be included in the proceedings of the DIS 2012 Workshop, Bonn, 26-30 March 2012. This online version contains updated references, and a note added on the latest results on resummation for jet-veto efficiencie

Status of resummed predictions for QCD final state observables

We provide a brief review of the current status of resummed predictions for QCD final state observables such as event shapes and jet rates in a variety of different hard processes. Particular emphasis is given to more recent developments such as the study of non global observables, development of generalized resummation formulae and resummations for new types of event shape variables.Comment: 7 pages. Invited talk at QCD 03, Montpellie

Dijet rates with symmetric E_t cuts

We consider dijet production in the region where symmetric cuts on the transverse energy, $E_t$, are applied to the jets. In this region next-to--leading order calculations are unreliable and an all-order resummation of soft gluon effects is needed, which we carry out. Although, for illustrative purposes, we choose dijets produced in deep inelastic scattering, our general ideas apply additionally to dijets produced in photoproduction or $\gamma \gamma$ processes and should be relevant also to the study of prompt di-photon $E_t$ spectra in association with a recoiling jet, in hadron-hadron processesComment: 28 pages, 4 figure