Abstract

Final states with photons in electron-positron collisions are studied in two complementary perspectives: an analysis of the QED Bremsstrahlung and an analysis of possible anomalous couplings between the Higgs boson and photons; using the data collected by DELPHI at a centre-of-mass energy of 183 GeV.

The QED Bremsstrahlung is analyzed in the production of $q\bar{q}$ pairs. There is a first study of the predictions of three different Monte Carlo generators and then the real data is compared with the predictions. It is found that the cross-section observed for the $q\bar{q}(\gamma)$ production in the Standard Model is above the Monte Carlo predictions and that the excess arises from events with hard and photons collinear to the beam.

The selected events are then used to determine the efficiency for separation between electrons and photons in the very forward region of DELPHI.

The existence of anomalous couplings of the Higgs boson to the gauge bosons is analyzed within an extension of the electroweak sector of the Standard Model assuming one Higgs doublet, gauge invariance and CP conservation. This analysis requires new calculations of the Higgs boson width, which are made for a Higgs boson mass between 60 GeV and 200 GeV. No signal is found for the existence of a Higgs boson with anomalous couplings to the gauge bosons. Limits on the minimum values of such couplings are derived as a function of the Higgs boson mass, assuming several scenarios for the relations between model parameters.

Keywords: photon, Quantum Electrodynamics, Bremsstrahlung, electron-photon separation, Higgs boson, anomalous couplings

DIV ALIGN="CENTER">

Estados Finais com Fotões

em LEP2

Radiação de Travagem da QED

e

Decaímentos Anómalos do Bosão de Higgs

Dissertação apresentada à

Faculdade de Ciências da Universidade de Lisboa

para obtenção do grau de mestre

Sofia Andringa Dias

Lisboa, 1999