Search for excited leptons in the data of the H1 experiment at the HERA collider

Composite models are one of the possible extensions of the Standard Model. One of their implications, at the energy in the reach of present particles accelerators, would be the excitation of leptons. This PhD. thesis describes the search for excited leptons with the H1 detector installed on the electron-proton collider HERA in Hamburg (Germany). The data used were accumulated between 1994 and 2000 and amount to an integrated luminosity of 120 pb-1. The analysis of 6 different topologies were done and cover all the branching ratios of desexcitation of excited electron and neutrino. The numbers of candidates found during those analysis is in agreement with the Standard Model expectations. This means that no evidence of excited leptons production was found at HERA. This result was translated in the form of exclusion limits on the coupling of excited leptons (f/A) depending on the mass of the excited lepton. For the first time at HERA we addressed the case were the natural decay width of the excited neutrino is wider than the experimental resolution. For the first time also, a study of the variation of limit depending on the ratio f' / f was carried out. This study lead to the setting of limits independent of this ratio. The limits obtained extend results previously obtained at HERA and also the results of direct searches at LEP. (orig.)