Testing the standard model at future high energy colliders

Abstract

Throughout this thesis we test some aspects of the Standard Model (SM) at future high energy colliders. We start by examining the SU(2)x U(l) non-abelian nature of the SM. We consider the effect of anomalous couplings on the reaction e(^+)e(^-) → W(^+)W-γ, at s = 200 GeV, where the photon is soft. We show that the dependence on the anomalous couplings is of the same order as, but different from, the dependence of the leading order e(^+)e(^-) → W(^+)W(^-) cross section. We therefore argue that the two processes are complementary in providing precision tests of the Standard Model electroweak vertices. We also study the same process, e(^+)e(^-) → W(^+)W(^-)γ, at high-energy e(^+)e(^-) colliders to investigate the effect of genuine quartic W(^+)W(^-)γγ and W(^+)W(^-)Zγ anomalous couplings on the cross section. Deviations from the Standard Model predictions are quantified. We show how bounds on the anomalous couplings can be improved by choosing specific initial state helicity combinations. The dependence of the anomalous contributions on the collider energy is studied. We then proceed to present a detailed analysis of soft photon radiation in e(^+)e(^-) → tt → bW(^+)bW(^-). The radiation pattern is shown to depend sensitively on the top mass, width and energy, as well as the relative orientation of the initial and final state particles. Optimum conditions in which initial state radiation is minimised and the radiation pattern has the richest structure are discussed. Finally, the Higgs sector of the SM is visited, where the production of the SM Higgs ø with intermediate mass at the proposed CERN LEPOLHC ep collider in γq(q) → W(^±)øq’(q), γq(q) → Zºøq(q) and gγ → qqø events is studied. This is done for all possible (massive) flavours of the quarks q(q') and using photons generated via Compton back-scattering of laser light. We study signatures in which the Higgs decays to bb-pairs and the electroweak vector bosons W(^±) and Zº decay either hadronically or leptonically. All possible backgrounds to these signals are also computed.