Electroweak radiative corrections to neutrino-nucleon scattering.

摘要

The main subject of this thesis is to study the impact of electroweak O (alpha) corrections on neutrino-nucleon scattering processes, in particular on the extraction of electroweak parameters at the NuTeV experiment.;The Standard Model (SM) represents the best current understanding of electroweak and strong interactions of elementary particles. In recent years it has been impressively confirmed experimentally through the precise determination of W and Z boson properties at the CERN LEP and the Stanford Linear e+e - colliders, and the discovery of the top quark at the Fermilab Tevatron pp collider.;The W boson mass (MW) is one of the fundamental parameters in electroweak theory. A precise measurement of MW does not only provide a further precisely known SM input parameter, but significantly improves the indirect limit on the Higgs-boson mass obtained by comparing SM predictions with electroweak precision data. MW is measured directly at the CERN LEP2 e+e- and the Fermilab Tevatron pp colliders. A measurement of MW can also be extracted from a measurement of the sine squared of the weak mixing angle, i.e. sin 2 thetaW, via the well-known relation between the W and Z boson mass, M2W=M2Z (1 - sin2 thetaW).;The NuTeV collaboration [20] extracts sin2 theta W, and thus MW, from the ratio of neutral and charged-current neutrino and anti-neutrino cross sections. Their result differs from direct measurements performed at LEP2 and the Fermilab Tevatron by about 3sigma.;Much effort both experimental and theoretical has gone into understanding this discrepancy. These efforts include QCD corrections, parton distribution functions, and nuclear structure [21]. However, the effect of electroweak radiative corrections has not been fully studied yet. In the extraction of MW from NuTeV data, only part of the electroweak corrections have been included [20]. Although the complete calculation of these corrections is available in [17] and [18], their impact on the NuTeV measurement of MW is not yet known.;In an attempt to answer this question, we calculated the complete electroweak O (alpha) corrections to neutrino--nucleon scattering and studied their impact on sin2 thetaW and MW measured by the NuTeV collaboration. We included in our calculation the full fermion-mass dependence, which has not been studied before. The result of the NuTeV collaboration is based on a calculation that neglects fermion masses whenever possible, i.e., they only keep fermion masses as regulators, as we have done when obtaining the massless result. We found that using the calculation with full fermion-mass dependence shifts sin2 thetaW by -0.0064(5) and consequently MW by +0.331(3) compared to the result obtained when considering massless fermions. Such a shift brings the NuTeV measurement of MW closer to the world average and thus could resolve the NuTeV anomaly. However, a more realistic study is needed including a simulation of the detector resolution, for instance.