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.