Search

We present the Fortran95 program Recola for the perturbative computation of next-to-leading-order transition amplitudes in the Standard Model of particle physics. The code provides numerical results in the 't Hooft-Feynman gauge. It uses the complex-mass scheme and allows for a consistent isolation of resonant contributions. Dimensional regularization is employed for ultraviolet and infrared singularities, with the alternative possibility of treating collinear and soft singularities in mass regularization. Recola supports various renormalization schemes for the electromagnetic and a dynamical Nf-flavour scheme for the strong coupling constant. The calculation of next-to-leading-order squared amplitudes, summed over spin and colour, is supported as well as the computation of colour- and spin-correlated leading-order squared amplitudes needed in the dipole subtraction formalism., Comment: 74 pages

We analyse the production of a Higgs boson in association with a top--antitop-quark pair in the Standard Model at the LHC. Considering the final state consisting of four b jets, two jets, one identified charged lepton and missing energy, we examine the irreducible background for the production rate and several kinematical distributions. While ttH production and decay is roughly a fourth of the full process for the final state specified above, ttbb production constitutes the main contribution with about $92\%$. Surprisingly, interference effects result in a reduction of the cross-section by five per cent. Furthermore, we consider NLO QCD corrections for the production of a Higgs boson, two charged leptons, two neutrinos, and two b jets. We discuss the size of the corrections and the scale dependence for the integrated cross section and different distributions. For the integrated cross section we find a $K$ factor of 1.17 and a reduction of the scale dependence from $30\%$ at leading order to $5\%$ at next-to-leading order., Comment: 10 pages, 3 figures, to appear in the Proceedings of the 12th International Symposium on Radiative Corrections (Radcor 2015) and LoopFest XIV (Radiative Corrections for the LHC and Future Colliders), UCLA, Los Angeles, USA, 2015

We present an analysis of Higgs-boson production in association with a top-quark pair at the LHC investigating in particular the final state consisting of four b jets, two jets, one identified charged lepton and missing energy. We consider the Standard Model prediction in three scenarios, the resonant Higgs-boson plus top-quark-pair production, the resonant production of a top-quark pair in association with a b-jet pair and the full process including all non-resonant and interference contributions. By comparing these scenarios we examine the irreducible background for the production rate and several kinematical distributions. With standard selection criteria the irreducible background turns out to be three times as large as the signal. For most observables we find a uniform deviation of eight percent between the scenario requiring two resonant top quarks and the full process. In particular phase-space regions the non-resonant contributions cause larger effects, and we observe shape changes for some distributions. Furthermore we investigate interference effects and find that neglecting interference contributions results in an over-estimate of the total cross-section of five percent., Comment: 23 pages, 29 eps figures

We compute the next-to-leading order corrections of $O(\alpha_s^2\alpha^3)$ to the hadronic production of two oppositely charged leptons and two hard jets, $p p \to j j l^- l^+$, using Recola and Collier. We include electroweak and QCD corrections at the given order and all off-shell effects. We provide detailed predictions for the LHC operating at 13 TeV and obtain per-cent-level corrections for the total cross section. For differential distributions we find significant non-uniform distortions in high-energy tails at the level of several ten per cent due to electroweak Sudakov logarithms and deformations at the level of a few per cent for angular variables., Comment: 28 pages, 24 eps figures

We present the computer code RECOLA for the computation of EW and QCD amplitudes in the Standard Model at next-to-leading order. One-loop amplitudes are represented as linear combinations of tensor integrals whose coefficients are calculated by means of recursive relations similar to Dyson-Schwinger equations. A novel treatment of colour enables us to recursively construct the colour structure of the amplitude efficiently. RECOLA is linked with the library COLLIER for the computation of the tensor integrals., Comment: 8 pages, to appear in the Proceedings of the 11th International Symposium on Radiative Corrections (Applications of Quantum Field Theory to Phenomenology), RADCOR 2013, Lumley Castle Hotel, Durham, UK, 2013

We present results for the electroweak radiative corrections to the production of a leptonically decaying Z boson in association with two jets at the LHC. Tree-level and one-loop amplitudes have been obtained with the computer code Recola for the recursive generation of tree-level and one-loop amplitudes in the Standard Model. The one-loop integrals have been calculated with the tensor-integral library Collier. The electroweak corrections turn out to be small for inclusive cross sections but can become large in tails of distributions., Comment: 8 pages, 4 eps figures, to appear in the Proceedings of the 11th International Symposium on Radiative Corrections (Applications of Quantum Field Theory to Phenomenology), RADCOR 2013, Lumley Castle Hotel, Durham, UK, 2013

We introduce the computer code Recola for the recursive generation of tree-level and one-loop amplitudes in the Standard Model. Tree-level amplitudes are constructed using off-shell currents instead of Feynman diagrams as basic building blocks. One-loop amplitudes are represented as linear combinations of tensor integrals whose coefficients are calculated similarly to the tree-level amplitudes by recursive construction of loop off-shell currents. We introduce a novel algorithm for the treatment of colour, assigning a colour structure to each off-shell current which enables us to recursively construct the colour structure of the amplitude efficiently. Recola is interfaced with a tensor-integral library and provides complete one-loop Standard Model amplitudes including rational terms and counterterms. As a first application we consider Z+2jets production at the LHC and calculate with Recola the next-to-leading-order electroweak corrections to the dominant partonic channels., Comment: 25 pages, 8 eps figures, section on accuracy and efficiency added, version to appear in JHEP

We consider top quark pair production in association with a hard jet through next-to-leading order in perturbative QCD. Top quark decays are treated in the narrow width approximation and spin correlations are retained throughout the computation. We include hard jet radiation by top quark decay products and explore their importance for basic kinematic distributions at the Tevatron and the LHC. Our results suggest that QCD corrections and jet radiation in decays can lead to significant changes in shapes of basic distributions and, therefore, need to be included for the description of ttbar+jet production. We compare the shape of the transverse momentum distribution of a top quark pair recently measured by the D0 collaboration with the result of our computation and find reasonable agreement., Comment: 22 pages, 8 figures

We compute QCD corrections to the production of a ttbar pair in association with a hard photon at the Tevatron and the LHC. This process allows a direct measurement of the top quark electromagnetic couplings that, at the moment, are only loosely constrained. We include top quark decays, treating them in the narrow width approximation, and retain spin correlations of final-state particles. Photon radiation off top quark decay products is included in our calculation and yields a significant contribution to the cross-section. We study next-to-leading order QCD corrections to the ppbar -> ttbar+gamma process at the Tevatron for the selection criteria used in a recent measurement by the CDF collaboration. We also discuss the impact of QCD corrections to the pp -> ttbar+gamma process on the measurement of the top quark electric charge at the 14 TeV LHC., Comment: 30 pages, 13 figures; extended reference list, update of quoted experimental efficiencies

Simultaneously with the turning-on of the Large Hadron Collider (LHC) the data taking for jet production rates will start. The study of these production rates is an important test of the Standard Model in the new energy regime accessible at the LHC. In order to discriminate possible extensions of the Standard Model accurate theoretical predictions are needed. We investigate the next-to-leading order weak corrections for bottom-quark jet and di-jet production at the LHC and find detectable effects in transverse momentum distributions., Comment: 6 pages, 9 figures, to be published in the proceedings of DPF-2009, Detroit, MI, July 2009, eConfC090726