P. Uwer

Theoretical status and prospects for top-quark pair production at hadron colliders

We present an update of the theoretical predictions for the cross section of top-quark pair production at Tevatron and LHC. In particular, we employ improvements due to soft-gluon resummation at next-to-next-to-leading logarithmic accuracy. We expand the resummed results and derive analytical finite-order cross sections through next-to-next-to-leading order which are exact in all logarithmically enhanced terms near threshold. These results are the best present estimates for the top-quark pair production cross section. We investigate the scale dependence as well as the sensitivity on the parton luminosities.

NLO QCD corrections to t anti-t + jet production at hadron colliders

We report on the calculation of the next-to-leading order QCD corrections to the production of top--anti-top quark pairs in association with a hard jet at the Tevatron and at the LHC. We present results for the t tbar + jet cross section and the forward--backward charge asymmetry. The corrections stabilize the leading-order prediction for the cross section. The charge asymmetry receives large corrections.

Hadronic top-quark pair production in association with a hard jet at next-to-leading order QCD: phenomenological studies for the Tevatron and the LHC

We report on the calculation of the next-to-leading order QCD corrections to the production of top–antitop-quark pairs in association with a hard jet at the Tevatron and at the LHC. Results for integrated and differential cross sections are presented. We find a significant reduction of the scale dependence. In most cases the corrections are below 20% indicating that the perturbative expansion is well under control. Moreover, the forward–backward charge asymmetry of the top quark, which is analyzed at the Tevatron, is studied at next-to-leading order. We find large corrections, suggesting that the definition of the observable has to be refined.

Top-Quark Spin Correlations at Hadron Colliders: Predictions at Next-to-Leading Order QCD

The collider experiments at the Tevatron and the LHC will allow for detailed investigations of the properties of the top quark. This requires precise predictions of the hadronic production of tt pairs and of their subsequent decays. In this Letter we present for the reactions pp, pp-->tt+X-->l+l-+X the first calculation of the dilepton angular distribution at next-to-leading order in the QCD coupling, keeping the full dependence on the spins of the intermediate tt state. The angular distribution reflects the degree of correlation of the t and t spins which we determine for different choices of t and t spin bases. In the case of the Tevatron, the QCD corrections are sizable, and the distribution is quite sensitive to the parton content of the proton.

QCD-corrected spin analysing power of jets in decays of polarized top quarks

Abstract We present results for the differential distributions of jets from non-leptonic decays of polarized top quarks within the Standard Model, including QCD radiative corrections. Our work extends existing results which are only available for semileptonic top quark decays at the parton level. For t (↑)→ b -jet+2 light jets we compute in particular the QCD-corrected top-spin analysing power of thexa0 b -quark jet and the least energetic light jet. The dependence of the results on the choice of the jet recombination scheme is found to be small. In addition we compute the spin analysing power of the thrust axis. Our results constitute a so far missing ingredient to analyse top quark production and subsequent non-leptonic decay at next-to-leading order in α s , keeping the full information on the top quark polarization.

Next-to-Leading-Order QCD Corrections toWW+JetProduction at Hadron Colliders

We report on the calculation of the next-to-leading order QCD corrections to the production of W-boson pairs in association with a hard jet at the Tevatron and the LHC, which is an important source of background for Higgs and new-physics searches. The corrections stabilize the leading-order prediction for the cross section considerably, in particular if a veto against the emission of a second hard jet is applied.

Heavy-quark pair production at two loops in QCD

We present updated predictions for the total cross section of top-quark pair production at Tevatron and LHC. For the LHC we also provide results at s = 10 TeV , in view of the anticipated run in 2008 and quote numbers for the production of new heavy-quark pairs with mass in the range 0.5 – 2 TeV. Our two-loop results incorporate all logarithmically enhanced terms near threshold including Coulomb corrections as well as the exact dependence on the renormalization and factorization scale through next-to-next-to-leading order in QCD.

Two-loop amplitudes with nested sums: Fermionic contributions toe+e−→qq¯g

We present the calculation of the nf-contributions to the two-loop amplitude for e+ e- --> q qbar g and give results for the full one-loop amplitude to order eps^2 in the dimensional regularization parameter. Our results agree with those recently obtained by Garland et al.. The calculation makes extensive use of an efficient method based on nested sums to calculate two-loop integrals with arbitrary powers of the propagators. The use of nested sums leads in a natural way to multiple polylogarithms with simple arguments, which allow a straightforward analytic continuation.

Automating dipole subtraction

We report on automating the Catani-Seymour dipole subtraction which is a general procedure to treat infrared divergences in real emission processes at next-to-leading order in QCD. The automatization rests on three essential steps: the creation of the dipole terms, the calculation of the color linked squared Born matrix elements, and the evaluation of different helicity amplitudes. The routines have been tested for a number of complex processes, such as the real emission process g g → t t ¯ g g g .

NLO QCD corrections to pp→WW+jet+X

We report on a calculation of the next-to-leading order QCD corrections to the production of W-boson pairs in association with a hard jet at hadron colliders, which is an important source of background for Higgs and new-physics searches at the LHC. If a veto against the emission of a second hard jet is applied, the corrections stabilize the leading-order prediction for the cross section considerably.