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Register a new userNext-to-Leading Order QCD Corrections to the Drell-Yan Cross Section in Models of TeV-Scale Gravity
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The first results on next-to-leading order QCD corrections to graviton-induced processes in hadron collisions in models of TeV-scale gravity are presented focusing on the case of dilepton pair production in bar p p and pp collisions. Distributions in the invariant mass Q, the longitudinal fraction x_F, the rapidity Y and the forward-backward asymmetry of the lepton pair are studied. The quantitative impact of the QCD corrections for searches of extra dimensions at hadron colliders is investigated. It turns out that at the LHC (sqrt{S}=14 TeV) the K-factor is rather large (K=1.6) for large invariant mass Q of the lepton pair, indicating the importance of accounting for these QCD corrections in the experimental search for TeV-scale gravity. At the Tevatron, the K-factor does not substantially deviate from the Standard Model value. However, its inclusion is necessitated to make the cross-section stable with respect to scale variations.
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We present phenomenological results for the inclusive cross section for the production of a lepton-pair via virtual photon exchange at next-to-next-to-next-to-leading order (N$^3$LO) in perturbative QCD. In line with the case of Higgs production, we find that the hadronic cross section receives corrections at the percent level, and the residual dependence on the perturbative scales is reduced. However, unlike in the Higgs case, we observe that the uncertainty band derived from scale variation is no longer contained in the band of the previous order.
We present an implementation of electroweak Z-boson production in association with two jets at hadron colliders in the POWHEG framework, a method that allows the interfacing of NLO-QCD calculations with parton-shower Monte Carlo programs. We focus on the leptonic decays of the weak gauge boson, and take photonic and non-resonant contributions to the matrix elements fully into account. We provide results for observables of particular importance for the suppression of QCD backgrounds to vector-boson fusion processes by means of central-jet-veto techniques. While parton-shower effects are small for most observables associated with the two hardest jets, they can be more pronounced for distributions that are employed in central-jet-veto studies.
The relevance of single-W and single-Z production processes at hadron colliders is well known: in the present paper the status of theoretical calculations of Drell-Yan processes is summarized and some results on the combination of electroweak and QCD corrections to a sample of observables of the process $p p to W^pm to mu^pm + X$ at the LHC are discussed. The phenomenological analysis shows that a high-precision knowledge of QCD and a careful combination of electroweak and strong contributions is mandatory in view of the anticipated LHC experimental accuracy. One of the authors (O.N.) dedicates these notes to Prof. S. Jadach, in honour of his 60th birthday and grateful for all that Prof. Jadach taught him during their fruitful collaboration.
An analytic formula is given for the total scattering cross section of an electron and a photon at order $alpha^3$. This includes both the double-Compton scattering real-emission contribution as well as the virtual Compton scattering part. When combined with the recent analytic result for the pair-production cross section, the complete $alpha^3$ cross section is now known. Both the next-to-leading order calculation as well as the pair-production cross section are computed using modern multiloop calculation techniques, where cut diagrams are decomposed into a set of master integrals that are then computed using differential equations.
We present predictions for the total ttbar production cross section sigma_ttbar at the Tevatron and LHC, which include the resummation of soft logarithms and Coulomb singularities through next-to-next-to-leading logarithmic order, and ttbar bound-state contributions. Resummation effects amount to about 8 % of the next-to-leading order result at Tevatron and about 3 % at LHC with 7 TeV centre-of-mass energy. They lead to a significant reduction of the theoretical uncertainty. With m_t=173.3 GeV, we find sigma_ttbar=7.22^{+0.31+0.71}_{-0.47-0.55} pb at Tevatron and sigma_ttbar=162.6^{+7.4+15.4}_{-7.5-14.7} at the LHC, in good agreement with the latest experimental measurements.
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