M. Czakon

Dominant QCD Backgrounds in Higgs Boson Analyses at the LHC: A Study of pp{yields}tt+2 Jets at Next-to-Leading Order

We report the results of a next-to-leading order simulation of top quark pair production in association with two jets. With our inclusive cuts, we show that the corrections with respect to leading order are negative and small, reaching 11%. The error obtained by scale variation is of the same order. Additionally, we reproduce the result of a previous study of top quark pair production in association with a single jet.

Polarizing the dipoles

We extend the massless dipole formalism of Catani and Seymour, as well as its massive version as developed by Catani, Dittmaier, Seymour and Trocsanyi, to arbitrary helicity eigenstates of the external partons. We modify the real radiation subtraction terms only, the primary aim being an improved efficiency of the numerical Monte Carlo integration of this contribution as part of a complete next-to-leading order calculation. In consequence, our extension is only applicable to unpolarized scattering. Upon summation over the helicities of the emitter pairs, our formulae trivially reduce to their original form. We implement our extension within the framework of textsc{Helac-Phegas}, and give some examples of results pertinent to recent studies of backgrounds for the LHC. The code is publicly available. Since the integrated dipole contributions do not require any modifications, we do not discuss them, but they are implemented in the software.

Hadronic top-quark pair production in association with two jets at Next-to-Leading Order QCD

We report on the calculation of the next-to-leading order QCD corrections to the production of t¯ pairs in association with two hard jets at the Fermilab TeVatron and CERN Large Hadron Collider. Results for the integrated and differential cross sections are given. The corrections with respect to leading order are negative and moderate. A study of the scale dependence of our NLO predictions indicates that the residual theoretical uncertainty, due to higher order corrections, is 21% for the TeVatron and 15% for the LHC. In case of the TeVatron, the forward-backward asymmetry of the top quark is calculated for the first time at next-to-leading order. With the inclusive selection of cuts, this asymmetry amounts to A t,LO = 10.3% at leading order and A t,NLO = 4.6% at next-to-leading order. All results presented in this paper have been obtained with the help of the Helac-Nlo package.

Matching the Nagy-Soper parton shower at next-to-leading order

A bstractWe present an Mc@Nlo-like matching of next-to-leading order QCD calculations with the Nagy-Soper parton shower. An implementation of the algorithm within the Helac-Dipoles Monte Carlo generator is used to address the uncertainties and ambiguities of the matching scheme. First results obtained using the Nagy-Soper parton shower implementation in Deductor in conjunction with the Helac-Nlo framework are given for the pp→tt¯j+X

Quantifying quark mass effects at the LHC: A study of pp -> b anti-b b anti-b + X at next-to-leading order

ppto toverline{t}j+X

pp \to b\bar bb\bar b + X

process at the LHC with s=8

Quantifying quark mass effects at the LHC: a study of \( pp\ \to\ b\overline{b}b\overline{b}+X \) at next-to-leading order

sqrt{s}=8