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Stefan Dittmaier

Publications and source records attributed to Stefan Dittmaier.

At least 91 records · Page 5Linked to original sources
arXiv2008

NLO QCD corrections to top anti-top bottom anti-bottom production at the LHC: 1. quark-antiquark annihilation

The process pp -> top anti-top bottom anti-bottom + X represents a very important background reaction to searches at the LHC, in particular to top anti-top H production where the Higgs boson decays into a bottom anti-bottom pair. A successful analysis of top anti-top H at the LHC requires the knowledge of direct top anti-top bottom anti-bottom production at next-to-leading order in QCD. We take the first step in this direction upon calculating the next-to-leading-order QCD corrections to the subprocess initiated by quark anti-quark annihilation. We devote an appendix to the general issue of rational terms resulting from ultraviolet or infrared (soft or collinear) singularities within dimensional regularization. There we show that, for arbitrary processes, in the Feynman gauge, rational terms of infrared origin cancel in truncated one-loop diagrams and result only from trivial self-energy corrections.

hep-ph↗
arXiv2008

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.

hep-ph↗
arXiv2008

Strong and electroweak NLO corrections to Higgs-boson production in vector-boson fusion at the LHC

We present results on the strong and electroweak NLO corrections to the production of a Higgs boson plus two hard jets via weak interactions at the LHC. The calculation includes all weak-boson fusion and quark-antiquark annihilation diagrams as well as all related interferences. We discuss corrections of different origin (QCD corrections of vector-boson-fusion type and interferences, electroweak corrections induced by quark or photonic initial states, heavy-Higgs-boson effects, etc.) and give some new results for distributions for a Higgs-boson mass of 200 GeV. The electroweak corrections are of the same size as the QCD corrections, viz. typically at the level of 5-10% for a Higgs-boson mass up to \sim 700 GeV. In general, they do not simply rescale differential distributions, but induce distortions at the level of 10%. The discussed corrections have been implemented in a flexible Monte Carlo event generator.

hep-ph↗
arXiv2008

NLO QCD corrections to pp -> top anti-top + jet + X

We discuss the production of top--anti-top quark pairs in association with a hard jet at the Tevatron and at the LHC and we report on the calculation of the next-to-leading order QCD corrections to this process. Numerical results for the top--anti-top+jet cross section and the forward--backward charge asymmetry are presented. The corrections stabilize the leading-order prediction for the cross section. In contrast, the charge asymmetry receives large corrections. The dependence of the cross section as well as the asymmetry on the minimum transverse momenta used to define the additional jet is studied in detail for the Tevatron.

hep-ph↗
arXiv2008

Radiative corrections to W-boson hadroproduction: higher-order electroweak and supersymmetric effects

The high accuracy envisaged for future measurements of W-boson production at hadron colliders has to be matched by precise theoretical predictions. We study the impact of electroweak radiative corrections on W-boson production cross sections and differential distributions at the Tevatron and at the LHC. In particular, we include photon-induced processes, which contribute at O(alpha), and leading radiative corrections beyond O(alpha) in the high-energy Sudakov regime and from multi-photon final-state radiation. We furthermore present the calculation of the complete supersymmetric next-to-leading-order electroweak and QCD corrections to W-boson hadroproduction within the MSSM. The supersymmetric corrections turn out to be negligible in the vicinity of the W resonance in general, reaching the percent level only at high lepton transverse momentum and for specific choices of the supersymmetric parameters.

hep-ph↗
arXiv2008

Polarized QED splittings of massive fermions and dipole subtraction for non-collinear-safe observables

Building on earlier work, the dipole subtraction formalism for photonic corrections is extended to various photon--fermion splittings where the resulting collinear singularities lead to corrections that are enhanced by logarithms of small fermion masses. The difference to the earlier treatment of photon radiation is that now no cancellation of final-state singularities is assumed, i.e. we allow for non-collinear-safe final-state radiation. Moreover, we consider collinear fermion production from incoming photons, forward-scattering of incoming fermions, and collinearly produced fermion-antifermion pairs. For all cases we also provide the corresponding formulas for the phase-space slicing approach, and particle polarization is supported for all relevant situations. A comparison of numerical results obtained with the proposed subtraction procedure and the slicing method is explicitly performed for the sample process e- gamma -> e- mu- mu+.

hep-ph↗
arXiv2008

Charged-Higgs Collider Signals with or without Flavor

A charged Higgs boson is a clear signal for an extended Higgs sector, as for example predicted by supersymmetry. Squark mixing can significantly change the pattern of charged-Higgs production and most notably circumvent the chiral suppression for single Higgs production. We evaluate the LHC discovery potential in the light of flavor physics, in the single-Higgs production channel and in association with a hard jet for small and moderate values of tan beta. Thoroughly examining current flavor constraints we find that non-minimal flavor structures can have a sizeable impact, but tend to predict moderate production rates. Nevertheless, charged-Higgs searches will probe flavor structures not accessible to rare kaon, bottom, or charm experiments, and can invalidate the assumption of minimal flavor violation.

hep-ph↗
arXiv2007

NLO QCD corrections to pp->WW+jet+X

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 hadron colliders, which is an important source of background for Higgs and new-physics searches. 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.

hep-ph↗
arXiv2007

Electroweak and QCD corrections to Higgs-boson production in vector-boson fusion at the LHC

Radiative corrections of strong and electroweak interactions are presented at next-to-leading order for Higgs-boson production in the weak-boson-fusion channel at the LHC. The calculation includes all weak-boson fusion and quark-antiquark annihilation diagrams as well as all related interferences. The electroweak corrections, which also include real corrections from incoming photons and leading heavy-Higgs-boson effects at two-loop order, are of the same size as the QCD corrections, viz. typically at the level of 5-10% for a Higgs-boson mass up to \sim 700 GeV. In general, they do not simply rescale differential distributions, but induce distortions at the level of 10%. The discussed corrections have been implemented in a flexible Monte Carlo event generator.

hep-ph↗
arXiv2007

Electroweak and QCD corrections to Higgs production via vector-boson fusion at the LHC

The radiative corrections of the strong and electroweak interactions are calculated at next-to-leading order for Higgs-boson production in the weak-boson-fusion channel at hadron colliders. Specifically, the calculation includes all weak-boson fusion and quark--antiquark annihilation diagrams to Higgs-boson production in association with two hard jets, including all corresponding interferences. The results on the QCD corrections confirm that previously made approximations of neglecting s-channel diagrams and interferences are well suited for predictions of Higgs production with dedicated vector-boson fusion cuts at the LHC. The electroweak corrections, which also include real corrections from incoming photons and leading heavy-Higgs-boson effects at two-loop order, are of the same size as the QCD corrections, viz. typically at the level of 5-10% for a Higgs-boson mass up to \sim 700 GeV. In general, both types of corrections do not simply rescale differential distributions, but induce distortions at the level of 10%. The discussed corrections have been implemented in a flexible Monte Carlo event generator.

hep-ph↗
arXiv2007

MSSM Higgs-boson production in bottom-quark fusion: electroweak radiative corrections

Higgs-boson production in association with bottom quarks is an important discovery channel for supersymmetric Higgs particles at hadron colliders for large values of tan(beta). We present the complete O(alpha) electroweak and O(alpha_s) strong corrections to associated bottom-Higgs production through bb fusion in the MSSM and improve this next-to-leading-order prediction by known two-loop contributions to the Higgs self-energies, as provided by the program FeynHiggs. Choosing proper renormalization and input-parameter schemes, the bulk of the corrections (in particular the leading terms for tan(beta)) can be absorbed into an improved Born approximation. The remaining non-universal corrections are typically of the order of a few per cent. Numerical results are discussed for the benchmark scenarios SPS 1b and SPS 4.

hep-ph↗
arXiv2004

Higgs Radiation off Bottom Quarks at the Tevatron and the LHC

Higgs-boson production in association with bottom quarks, ppbar/pp -> b bbar H + X, is one of the most important discovery channels for supersymmetric Higgs particles at the Tevatron and the LHC. We have calculated the next-to-leading order QCD corrections to the parton processes qqbar,gg -> bbbar H and present results for total cross sections and for distributions in the transverse momenta of the bottom quarks. The QCD corrections reduce the renormalization and factorization scale dependence and thus stabilize the theoretical predictions, especially when the Higgs boson is produced in association with high-pT bottom quarks. The next-to-leading order predictions for the total cross section are in reasonable numerical agreement with calculations based on bottom-quark fusion bbbar ->H.

hep-ph↗
arXiv2003

Separation of soft and collinear singularities from one-loop N-point integrals

The soft and collinear singularities of general scalar and tensor one-loop N-point integrals are worked out explicitly. As a result a simple explicit formula is given that expresses the singular part in terms of 3-point integrals. Apart from predicting the singularities, this result can be used to transfer singular one-loop integrals from one regularization scheme to another or to subtract soft and collinear singularities from one-loop Feynman diagrams directly in momentum space.

hep-ph↗
arXiv2002

Associated Higgs production with heavy quark pairs at hadron colliders

The reactions p\bar{p}/pp -> t\bar{t}H+X represent important channels in the search for the Standard Model Higgs boson at the Tevatron and the LHC. In the leading perturbative order the cross sections suffer from severe (renormalization and factorization) scale uncertainties. The next-to-leading order QCD corrections stabilize the cross sections considerably. The calculation of these corrections is briefly reviewed, and a few numerical results are discussed.

hep-ph↗
arXiv2002

Six-fermion production at e+e- colliders

The class of six-fermion production processes at e+e- colliders comprises very interesting particle reactions, such as the production of top-quark pairs and of Higgs bosons in the intermediate Higgs mass range, the scattering of massive gauge bosons, and triple gauge-boson production. The Monte Carlo event generator LUSIFER is designed for the analysis of such processes. A few illustrating results obtained with LUSIFER are discussed.

hep-ph↗
arXiv2002

LUSIFER: a LUcid approach to SIx-FERmion production

LUSIFER is a Monte Carlo event generator for all processes e+e-->6fermions, which is based on the multi-channel Monte Carlo integration technique and employs the full set of tree-level diagrams. External fermions are taken to be massless, but can be arbitrarily polarized. The calculation of the helicity amplitudes and of the squared matrix elements is presented in a compact way. Initial-state radiation is included at the leading logarithmic level using the structure-function approach. The discussion of numerical results contains a comprehensive list of cross sections relevant for a 500GeV collider, including a tuned comparison to results obtained with the combination of the WHIZARD and MADGRAPH packages as far as possible. Moreover, for off-shell top-quark pair production and the production of a Higgs boson in the intermediate mass range we additionally discuss some phenomenologically interesting distributions. Finally, we numerically analyze the effects of gauge-invariance violation by comparing various ways of introducing decay widths of intermediate top quarks, gauge and Higgs bosons.

hep-ph↗
arXiv2002

Photonic and QCD radiative corrections to Higgs-boson production in mu+ mu- --> f fbar

The photonic and QCD radiative corrections at next-to-leading order are calculated for fermion-pair production at muon colliders, maintaining the full mass dependence and helicity information of the muons and the produced fermions. Higher-order effects of initial-state radiation are included at the leading logarithmic level. In the calculation particular attention is paid to the issue of gauge invariance in the vicinity of resonances. The most important corrections are presented in analytical form. The detailed numerical discussion concentrates on the corrections to the (s-channel) Higgs-boson resonances in the Standard Model and its minimal supersymmetric extension. The results show that photonic initial- and QCD final-state corrections are very important in a precision study of Higgs resonances, but that (photonic) initial-final interferences are widely suppressed and only modify the non-resonant background.

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