Search for composite and exotic fermions at LEP 2

Abstract

A search for unstable heavy fermions with the DELPHI detector at LEP is reported. Sequential and non-canonical leptons, as well as excited leptons and quarks, are considered. The data analysed correspond to an integrated luminosity of about 48 pb $^{-1}$ at an $\rm e^+e^-$ centre-of-mass energy of 183 GeV and about 20 pb $^{-1}$ equally shared between the centre-of-mass energies of 172 GeV and 161 GeV. The search for pair-produced new leptons establishes 95% confidence level mass limits in the region between 70 GeV/ $c^2$ and 90 GeV/ $c^2$ , depending on the channel. The search for singly produced excited leptons and quarks establishes upper limits on the ratio of the coupling of the excited fermion to its mass ( $\lambda/m_{f^*}$ ) as a function of the mass.