Probing the standard model and beyond at high-energy colliders

Abstract

The thesis covers the following topics: Assuming a partonic structure of the Pomeron we give predictions for diffractive heavy flavour production at the Tevatron and the LHC and diffractive Higgs production at the LHC in leading-order approximation. For the latter the dominant background processes are also considered. We obtain results on single as well as double diffractive cross sections assuming a Donnachie-Landshoff-type Pomeron flux factor. Measurements of the single inclusive jet cross section at the Tevatron by the CDF Collaboration maybe suggest a modified picture of QCD in the large E(_T) range. A parameter fit of a neutral heavy vector boson Z(^1) to the CDF data, in leading order perturbation theory, is performed, and the question of how the corresponding single inclusive jet cross-sections and the dijet angular distributions at the LHC are affected by this additional Z' is discussed. We test a model, motivated by the former R(_b) and R(_c) "crisis", which contains extra vector fermions. We suggest an alternative indirect test of the possible existence of new heavy quark flavours at the LEP2 collider, which turns out to give the clearest signal. We calculate qq cross sections within this framework, including one loop corrections. Hadronic antenna patterns can provide a valuable diagnostic tool for probing the origin of the reported excess of high x, Q(^2) events at HERA. We present quantitative predictions for the distributions of soft particles and jets in standard deep inelastic scattering eq → eq events and in events corresponding to the production of a narrow colour-triplet scalar resonance. We also study the patterns corresponding to Higgs production and decay in high- energy hadron-hadron collisions. In particular, the signal gg → H → bb and background gg → bb processes are shown to have very different radiation patterns, and this may provide a useful additional method for distinguishing Higgs signal events from the QCD background. The process eq → eq + γ exhibits radiation zeros, i.e. configurations of the final-state particles for which the scattering amplitude vanishes. We study these zeros for both e(^+)u and e(^+)d scattering. The latter exhibits a new type of zero which to our knowledge has not previously been identified. The observability of radiation zeros at HERA is discussed. In the framework of this new type of zero we also study the process e(^+)e(^-) → qqγ. We calculate the positions of these zeros for u-quark and d-quark production and assess the feasibifity of identifying the zeros in experiments at high energies. The radiation zeros are shown to occur also for massive quarks, and we discuss how the bbγ final state may offer a particularly clean environment in which to observe them.