On the NLO QCD corrections to Higgs production and decay in the MSSM

We present explicit analytic results for the two-loop top/stop/gluino contributions to the cross section for the production of CP-even Higgs bosons via gluon fusion in the MSSM, under the approximation of neglecting the Higgs boson mass with respect to the masses of the particles circulating in the loops. The results are obtained employing the low-energy theorem for Higgs interactions adapted to the case of particle mixing. We discuss the validity of the approximation used by computing the first-order correction in an expansion in powers of the Higgs boson mass. We find that, for the lightest CP-even Higgs boson, the gluino contribution is very well approximated by the result obtained in the limit of vanishing Higgs mass. As a byproduct of our calculation, we provide results for the two-loop QCD contributions to the photonic Higgs decay.     

The one-loop renormalization of the MSSM Higgs sector and its application to the neutral scalar Higgs masses

The structure of the Higgs sector in the minimal supersymmetric standard model is reviewed at the oneloop level. An on-shell renormalization scheme of the MSSM Higgs sector is presented in detail together with the complete list of formulae for the neutral Higgs masses at the one-loop level. The results of a complete one-loop calculation for the mass spectrum of the neutral MSSM Higgs bosons and the quality of simpler Born-like approximations are discussed for sfermion and gaugino masses in the range of the electroweak scale.     

NLO electroweak corrections to Higgs boson production at hadron colliders

Results for the complete NLO electroweak corrections to Standard Model Higgs production via gluon fusion are included in the total cross section for hadronic collisions. Artificially large threshold effects are avoided working in the complex-mass scheme. The numerical impact at LHC (Tevatron) energies is explored for Higgs mass values up to 500 GeV (200 GeV). Assuming a complete factorization of the electroweak corrections, one finds a +5% shift with respect to the NNLO QCD cross section for a Higgs mass of 120 GeV both at the LHC and the Tevatron. Adopting two different factorization schemes for the electroweak effects, an estimate of the corresponding total theoretical uncertainty is computed.     

Standard SANC modules for NLO QCD radiative corrections to single top-quark production

In this paper we present the results obtained with the newly created standard SANC modules for calculation of the NLO QCD corrections to single top-quark-production processes in s and t channels at the partonic level, as well as to top-decays. The main aim of these results is to prove the correct work of modules. A comprehensive comparison with the results of the CompHEP system is given, where possible. These modules are intended to be used in Monte Carlo generators for single top-quark-production processes at the LHC. As in our recent paper, devoted to the electroweak corrections to these processes, we study the regularization of the top-legs associated infrared divergences with the aid of the complex mass of the top quark. A comparison of QCD corrections with those computed by the conventional method is presented both for top production and for decays. For s-channel production we give an analytic proof of equivalence of the two methods in the limit of low top width.     

SUSY background to neutral MSSM Higgs boson searches

Within the Minimal Supersymmetric Standard Model (MSSM) the production and decay of superpartners can give rise to backgrounds for Higgs boson searches. Here MSSM background processes to the vector boson fusion channel with the Higgs boson decaying into two tau leptons or two W-bosons are investigated, giving rise to dilepton plus missing transverse momentum signals of the Higgs boson. Starting from a scenario with relatively small masses of the supersymmetric (SUSY) particles, with concomitant large cross section of the background processes, one obtains a first conservative estimate of the background. Light chargino pair production plus two jets, lightest and next-to-lightest neutralino production plus two jets as well as slepton pair production plus two jets are identified as important contributions to the irreducible SUSY background. Light chargino and next-to-lightest neutralino production plus two jets and next-to-lightest neutralino pair production plus two jets give rise to reducible backgrounds, which can be larger than the irreducible ones in some scenarios. The relevant distributions are shown and additional cuts for MSSM background reduction are discussed. Extrapolation to larger squark masses is performed and shows that MSSM backgrounds are quite small for squark masses at the current exclusion limits.     

Two-loop SUSY QCD corrections to the chargino masses in the MSSM

We have calculated the two-loop strong interaction corrections to the chargino pole masses in the scheme in the minimal supersymmetric standard model with complex parameters. We have performed a detailed numerical analysis for a particular point in the parameter space and found corrections of a few tenths of a percent. We provide a computer program that calculates chargino and neutralino masses with complex parameters up to .     

NLO QCD corrections to Drell-Yan processes in the SANC framework

NLO QCD corrections to charged and neutral current Drell-Yan processes are computed with help of the computer system SANC. At the partonic level both quark-antiquark and quark-gluon scattering channels are taken into account. Subtraction of collinear singularities in the massive quark scheme is compared with the one in the $ \overline {MS} $ \overline {MS} scheme. Numerical results at the hadronic level are received for the LHC conditions with help of Monte-Carlo integrators and event generator programs based on the standard SANC modules. Comparison with analogous results of the MCFM package is shown.     

A search for neutral Higgs bosons in the MSSM and models with two scalar field doublets

A search is described for the neutral Higgs bosons and predicted by models with two scalar field doublets and, in particular, the Minimal Supersymmetric Standard Model (MSSM). The search in the and production channels is based on data corresponding to an integrated luminosity of 25 pb from collisions at centre-of-mass energies between 130 and 172 GeV collected with the OPAL detector at LEP. The observation of a number of candidates consistent with Standard Model background expectations is used in combination with earlier results from data collected at the resonance to set limits on and in general models with two scalar field doublets and in the MSSM. For example, in the MSSM, for , minimal and maximal scalar top quark mixing and soft SUSY-breaking masses of 1 TeV, the 95% confidence level limits GeV and GeV are obtained. For the first time, the MSSM parameter space is explored in a detailed scan. Received: 20 February 1998 / Published online: 13 July 1998     

Higher-order corrections to Higgs boson decays in the MSSM with complex parameters

We discuss Higgs boson decays in the CP-violating MSSM, and examine their phenomenological impact using cross section limits from the LEP Higgs searches. This includes a discussion of the full 1-loop results for the partial decay widths of neutral Higgs bosons into lighter neutral Higgs bosons (h _a →h _b h _c ) and of neutral Higgs bosons into fermions (\(h_{a} \to f \bar{f}\)). In calculating the genuine vertex corrections, we take into account the full spectrum of supersymmetric particles and all complex phases of the supersymmetric parameters. These genuine vertex corrections are supplemented with Higgs propagator corrections incorporating the full 1-loop and the dominant 2-loop contributions, and we illustrate a method of consistently treating diagrams involving mixing with Goldstone and Z bosons. In particular, the genuine vertex corrections to the process h _a →h _b h _c are found to be very large and, where this process is kinematically allowed, can have a significant effect on the regions of the CPX benchmark scenario which can be excluded by the results of the Higgs searches at LEP. However, there remains an unexcluded region of CPX parameter space at a lightest neutral Higgs boson mass of ～45 GeV. In the analysis, we pay particular attention to the conversion between parameters defined in different renormalisation schemes and are therefore able to make a comparison to the results found using renormalisation group improved/effective potential calculations.     

Note on QCD corrections to hadronic Higgs decay

The O(_s) QCD correction to the hadronic decay of a scalar Higgs boson, for which contradicting results have been reported, is calculated. Our result is in agreement with that of Braaten and Leveille but disagrees with that of Janot. The possible origin of the discrepancy is discussed. The total hadronic decay rate and the differential rate to q g of a pseudoscalar Higgs boson are also presented.