Approximate NNLO Threshold Resummation in Heavy Flavour Decays

We present an approximate NNLO evaluation of the QCD form factor resumming large logarithmic perturbative contributions in semi-inclusive heavy flavour decays.Comment: 16 pages, 3 figures, Latex; minor changes; 2 figures adde

Measurement of triple differential photon plus jet cross section by D0

We report on a new measurement of triple differential cross section for the process ppbar -> photon + jet + X in ppbar collisions at sqrt(s)=1.96 TeV by the D0 Collaboration at Fermilab based on a dataset corresponding to an integrated luminosity of 1.1 fb-1.Comment: 3 pages, 1 figure, To appear in the Proceedings of the 2007 Europhysics Conference on High Energy Physics, Manchester, UK. Accepted for publication in Journal of Physics : Conference Serie

Direct Higgs production and jet veto at hadron colliders

We consider Higgs boson production through gluon--gluon fusion in hadron collisions, when a veto is applied on the transverse momenta of the accompanying hard jets. We compute the QCD corrections to this process at NLO and NNLO, and present numerical results at the Tevatron and the LHC.Comment: 5 pages, 4 ps figures, presented at the XXXVIIth Rencontres de Moriond, QCD and Hadronic interactions, Les Arc1800, Franc

A Tree-Loop Duality Relation at Two Loops and Beyond

The duality relation between one-loop integrals and phase-space integrals, developed in a previous work, is extended to higher-order loops. The duality relation is realized by a modification of the customary +i0 prescription of the Feynman propagators, which compensates for the absence of the multiple-cut contributions that appear in the Feynman tree theorem. We rederive the duality theorem at one-loop order in a form that is more suitable for its iterative extension to higher-loop orders. We explicitly show its application to two- and three-loop scalar master integrals, and we discuss the structure of the occurring cuts and the ensuing results in detail.Comment: 20 pages. Few typos corrected, some additional comments included, Appendix B and one reference added. Final version as published in JHE

Higgs production in hadron collisions: soft and virtual QCD corrections at NNLO

We consider QCD corrections to Higgs boson production through gluon-gluon fusion in hadron collisions. Using the recently evaluated two-loop amplitude for this process and the corresponding factorization formulae for soft-gluon bremsstrahlung at O(alpha_s^2), we compute the soft and virtual contributions to the NNLO cross section. We also discuss soft-gluon resummation at next-to-next-to-leading logarithmic accuracy. Numerical results for Higgs boson production at the LHC are presented.Comment: 17 pages, 4 figures included. One note and one reference adde

An NNLO subtraction formalism in hadron collisions and its application to Higgs boson production at the LHC

We consider higher-order QCD corrections to the production of colourless high-mass systems (lepton pairs, vector bosons, Higgs bosons,...) in hadron collisions. We propose a new formulation of the subtraction method to numerically compute arbitrary infrared-safe observables for this class of processes. To cancel the infrared divergences, we exploit the universal behaviour of the associated transverse-momentum (q_T) distributions in the small-q_T region. The method is illustrated in general terms up to the next-to-next-to-leading order (NNLO) in QCD perturbation theory. As a first explicit application, we study Higgs boson production through gluon fusion. Our calculation is implemented in a parton level Monte Carlo program that includes the decay of the Higgs boson in two photons. We present selected numerical results at the LHC.Comment: References adde

QCD at High Energies

The following topics in perturbative QCD are reviewed: recent theoretical progress in higher-order calculations; soft-gluon resummation for hard-scattering processes at large $E_T$ and high $x$; low-$x$ behaviour of structure functions and recent theoretical results on BFKL dynamics; infrared renormalons and power corrections to perturbative predictions; updated summary of \as measurements

A new jet algorithm based on the k-means clustering for the reconstruction of heavy states from jets

A jet algorithm based on the k-means clustering procedure is proposed which can be used for the invariant-mass reconstruction of heavy states decaying to hadronic jets. The proposed algorithm was tested by reconstructing E+ E- to ttbar to 6 jets and E+ E- to W+W- to 4 jets processes at \sqrt{s}=500 GeV using a Monte Carlo simulation. It was shown that the algorithm has a reconstruction efficiency similar to traditional jet-finding algorithms, and leads to 25% and 40% reduction of reconstruction width for top quarks and W bosons, respectively, compared to the kT (Durham) algorithm. In addition, it is expected that the peak positions measured with the new algorithm have smaller systematical uncertainty.Comment: 11 pages, 3 eps figures (Eur. Phys. J. C, in press

Initial-state parton shower kinematics for NLO event generators

We are developing a consistent method to combine tree-level event generators for hadron collision interactions with those including one additional QCD radiation from the initial-state partons, based on the limited leading-log (LLL) subtraction method, aiming at an application to NLO event generators. In this method, a boundary between non-radiative and radiative processes necessarily appears at the factorization scale (mu_F). The radiation effects are simulated using a parton shower (PS) in non-radiative processes. It is therefore crucial in our method to apply a PS which well reproduces the radiation activities evaluated from the matrix-element (ME) calculations for radiative processes. The PS activity depends on the applied kinematics model. In this paper we introduce two models for our simple initial-state leading-log PS: a model similar to the "old" PYTHIA-PS and a p_T-prefixed model motivated by ME calculations. PS simulations employing these models are tested using W-boson production at LHC as an example. Both simulations show a smooth matching to the LLL-subtracted W + 1 jet simulation in the p_T distribution of W bosons, and the summed p_T spectra are stable against a variation of mu_F, despite that the p_T-prefixed PS results in an apparently harder p_T spectrum.Comment: 10 pages, 6 figures; minor changes in the abstract and the text according to the comments from the refere