The physics potential of the LHC

This talk is a short overview of the physics potential of the LHC with emphasis on Higgs search and SUSY search. First I review why LHC with the ATLAS and CMS detectors is expected to give a decisive test of the electroweak symmetry breaking mechanism of the Standard Model. Then I consider the Higgs sector of the Standard Model (SM). Finally the search for supersymmetry is discussed within the framework of various implementation of the Minimal Supersymmetric Standard Model (MSSM).Comment: Talk given at the meeting Beyond The Standard Model V, Balholm, Norway April 29 -- May 4, 1997, 10 pages, 2 figure

Two photons plus jet al LHC: the NNLO contribution from the gg initiated process

The production of the Standard Model Higgs boson of mass ~ 100-140 GeV at the LHC likely gives clear signals in the $\gamma \gamma$ (1) and in the $\gamma \gamma jet$ (2) channels. The quantitative evaluation of the background to channel (1) is very hard since the next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) QCD corrections are large. In particular, the contributions of the NNLO QCD subprocess $gg -> \gamma \gamma$ to inclusive $\gamma\gamma$ production is comparable to the contribution of the leading order subprocess $q\bar{q} -> \gamma \gamma$. The quantitative description of the background to channel (1), therefore, requires to calculate all corrections up to the NNNLO level. In this letter we present results on the contribution of the NNLO QCD subprocess $gg -> g \gamma \gamma$ to the production rate of channel (2). We have found that in this case this NNLO contribution is less than 20% of the Born contribution. Since the NNLO contributions will likely be dominated by this subprocess one can argue that in the case of channel (2) - contrary to the case of channel (1)- a quantitative description of the background can be achieved already at next-to-leading order accuracy.Comment: 7 pages, two figures include

Choosing integration points for QCD calculations by numerical integration

I discuss how to sample the space of parton momenta in order to best perform the numerical integrations that lead to a calculation of three jet cross sections and similar observables in electron-positron annihilation.Comment: 25 pages with 8 figure

Techniques for QCD calculations by numerical integration

Calculations of observables in quantum chromodynamics are typically performed using a method that combines numerical integrations over the momenta of final state particles with analytical integrations over the momenta of virtual particles. I describe the most important steps of a method for performing all of the integrations numerically.Comment: 36 pages with 16 postscript figure

QCD Corrections and the Leptoquark Interpretation of the HERA High Q^2 Events

The excess of high-$Q^2$ events found by H1 and ZEUS at HERA in $e^+p$ deep-inelastic scattering above the Standard Model prediction motivates us to calculate the NLO QCD corrections to the HERA scalar leptoquark (or squark) production cross sections. We find that the corrections are significant, of order 50% in the mass range of interest. We also calculate the leptoquark average transverse momentum squared and find it to be rather small. Various leptoquark production cross sections at the Tevatron $p \bar p$ collider are also considered. We investigate in detail the leptoquark interpretation of the HERA data. First we assume a minimal leptoquark model with a single diagonal Yukawa coupling to first family lepton and quark mass eigenstates only. In this case constraints from atomic parity violating experiments allow only isodoublet scalar leptoquark production at HERA. This interpretation can be confirmed or ruled out in the near future by high luminosity data at the Tevatron. The Tevatron data already appear to rule out the vector leptoquark interpretation of the HERA data. We also consider a more general model which allows for all possible left-handed, right-handed, flavour and lepton number changing couplings. The allowed values of the Yukawa couplings of this general model offer several different interpretations of the data which are radically different from the minimal model solutions. However these somewhat ad hoc tuned solutions can easily be tested by future HERA experiments.Comment: 25 pages, LaTeX, incl. 3 postscript figures, uses epsf.st