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Michael Krämer

Publications and source records attributed to Michael Krämer.

At least 109 records · Page 6Linked to original sources
arXiv2009

Soft-gluon resummation for squark and gluino hadroproduction

We consider the resummation of soft gluon emission for squark and gluino hadroproduction at next-to-leading-logarithmic (NLL) accuracy in the framework of the minimal supersymmetric standard model. We present analytical results for squark-squark and squark-gluino production and provide numerical predictions for all squark and gluino pair-production processes at the Tevatron and at the LHC. The size of the soft-gluon corrections and the reduction in the scale uncertainty are most significant for processes involving gluino production. At the LHC, where the sensitivity to squark and gluino masses ranges up to 3 TeV, the corrections due to NLL resummation over and above the NLO predictions can be as high as 35% in the case of gluino-pair production, whereas at the Tevatron, the NLL corrections are close to 40% for squark-gluino final states with sparticle masses around 500 GeV.

hep-ph↗
arXiv2009

Charged-Higgs-boson production at the LHC: NLO supersymmetric QCD corrections

The dominant production process for heavy charged Higgs bosons at the LHC is the associated production with heavy quarks. We have calculated the next-to-leading-order supersymmetric QCD corrections to charged-Higgs production through the parton processes $q\bar{q},gg \to tbH^{\pm}$ and present results for total cross sections and differential distributions. The QCD corrections reduce the renormalization and factorization scale dependence and thus stabilize the theoretical predictions. We present a comparison of the next-to-leading-order results for the inclusive cross section with a calculation based on bottom--gluon fusion $gb \to tH^{\pm}$ and discuss the impact of the next-to-leading-order corrections on charged-Higgs searches at the LHC.

hep-ph↗
arXiv2008

Summary of the Electroweak and Beyond the Standard Model Working Group

A wide array of deep-inelastic-scattering and hadron collider experiments have tested the predictions of the electroweak theory and measured its parameters, while also searching for new particles and processes. We summarise recent measurements and searches that probe the Standard Model to unprecedented precision.

hep-ex↗
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

Squark Cascade Decays to Charginos/Neutralinos: Gluon Radiation

The momentum spectrum and the polarization of charginos and neutralinos in squark decays are affected by gluon radiation in the decay process \tilde{q} \to q \tildeχ (g). We determine these corrections and study their impact on the [ql] invariant mass distributions for leptonic \tildeχ decays. The higher-order corrections, though small in general, can be sizeable near pronounced edges of the final-state distributions.

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↗
arXiv2005

Next-to-leading order QCD jet production with parton showers and hadronization

We report on a method for matching the next-to-leading order calculation of QCD jet production in e+e- annihilation with a Monte Carlo parton shower event generator (MC) to produce realistic final states. The final result is accurate to next-to-leading order (NLO) for infrared-safe one-scale quantities, such as the Durham 3-jet fraction y_3, and agrees well with parton shower results for multi-scale quantities, such as the jet mass distribution in 3-jet events. For our numerical results, the NLO calculation is matched to the event generator Pythia, though the method is more general. We compare one scale and multi-scale quantities from pure NLO, pure MC, and matched NLO-MC calculations.

hep-ph↗
arXiv2004

Associated Higgs production with bottom quarks at hadron colliders

Higgs-boson production in association with bottom quarks is an important discovery channel for supersymmetric Higgs particles at the Tevatron and the LHC. We present higher-order QCD predictions for inclusive cross sections and for the production of a Higgs boson in association with high-p_T bottom quarks. We compare calculations performed in a four-flavour scheme based on the parton processes gg,qqbar -> b bbar H with five-flavour scheme calculations based on bottom-quark scattering.

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↗
arXiv2001

Quarkonium Production at High-Energy Colliders

The theoretical description of heavy quarkonium production at high-energy p-pbar and e-p colliders is reviewed. Predictions based on non-relativistic QCD factorisation are confronted with recent charmonium and bottomonium data from the Tevatron and HERA. Potential shortcomings of the present theoretical analyses are discussed, and the prospects for quarkonium physics at the upgraded Tevatron and HERA colliders and at the LHC are summarised.

hep-ph↗
arXiv2000

J/psi and psi(2S) Production and Polarization at the Tevatron

The NRQCD factorization approach for quarkonium production at hadron colliders is reviewed. The prediction of J/psi and psi(2S) transverse polarization at large transverse momentum is confronted with recent experimental data, and potential shortcomings of the theoretical analysis are discussed.

hep-ph↗
arXiv2000

Tests of QCD: Summary of DIS 2000

This summary of the working group 2 of DIS 2000 encompasses experimental and theoretical results of jet physics, open and bound state heavy flavour production, prompt photon production, next-to-leading order QCD calculations and beyond, instantons, fragmentation, event shapes, and power corrections, primarily from deep-inelastic scattering and photoproduction at HERA, but also from the LEP and Tevatron colliders.

hep-ph↗
arXiv2000

Heavy Flavour Production in Two-Photon Collisions

We review the production of charm and bottom quarks in two-photon collisions at e+e- colliders. The next-to-leading order QCD predictions for total cross sections and differential distributions are compared with recent experimental results.

hep-ph↗
arXiv1999

D* Production in Two-Photon Collisions

We calculate total and differential production rates of D* mesons in two-photon collisions at LEP2. We include full next-to-leading order QCD corrections, and perform an extensive study of the sensitivity of our predictions to variations of the renormalization scale, charm mass, photonic parton distribution set and fragmentation function. The results are compared with recent data from LEP2.

hep-ph↗
arXiv1999

QCD Corrections to Radiative Upsilon Decays

We have calculated the next-to-leading order perturbative QCD corrections to the photon energy spectrum in radiative Upsilon decays. The higher-order corrections significantly modify the shape of the spectrum, in particular at large photon energies, and thereby reduce the discrepancy between experimental data and previous leading-order predictions. The next-to-leading order calculation of the photon energy spectrum allows a more reliable determination of the strong coupling constant from radiative Upsilon decays by restricting the analysis to the region of the energy spectrum that can be described by NLO perturbation theory.

hep-ph↗
arXiv1999

Heavy-Flavour Production at HERA

We review the theoretical and experimental status of heavy-flavour production at HERA. The results presented include some outstanding issues in charm and beauty photoproduction, charm production in DIS and quarkonium production.

hep-ph↗