The QED coupling at the Z pole and jet studies of small χ dynamics

Abstract

In the first half of this thesis, motivated by significant progress in both theoretical and empirical studies of e(^+)e(^-) annihilation into hadrons, we perform a reevaluation of the running of the QED coupling to the Z-pole, paying particular attention to the hadronic contribution to vacuum polarization. We use a comprehensive collection of the presently available data and perturbative QCD expressions. This new determination of the running of the coupling is then used as input into a global fit to electroweak data to estimate a preferred value of the Standard Model Higgs boson. An estimate is obtained of M(_H) = 110 GeV, marginally above the zone excluded by direct searches at LEP2.We then investigate the potential for further constraining the hadronic contribution to the vacuum polarization function through mechanisms incorporating analytic continuation from the timelike domain of s < 0 around a large semicircle into the spacelike domain of s > 0. Intrinsic sensitivity in the QCD description to the pole masses force us to conclude there is no advantage to be gained in comparison with the direct timelike estimation, although by demanding consistency between the complementary approaches we can both generate an estimate of the charm mass and elucidate low energy data ambiguities, finding a preferred value of m(_c) = 1.4. In the latter half of the thesis, we examine forward jet and pion production in electron - proton deep inelastic scattering in the small x region of the HERA collider at DESY. We demonstrate the imposition of physically motivated dominant subleading corrections to all orders on the leading logarithmic BFKL equation, and that this leads to stable phenomenological predictions. We compare the calculations of differential cross-section distributions incorporating the higher order effects with the experimental profiles for a single jet, an identified and dijets in the very forward region and investigate the sensitivity of the calculation to residual parametric freedom.