Search for a scalar top almost degenerate with the lightest neutralino in e+e− collisions at s up to 202 GeV

Data collected at centre-of-mass energies from 189 GeV to 202 GeV by the ALEPH detector at LEP, corresponding to an integrated luminosity of 411 pb-1, are analysed in a search for the scalar top in the decay channels 'stop -> c/u neutralino' for small mass differences between the stop and the lightest neutralino. No evidence for deviations from the Standard Model expectation is found and a lower limit of 59 GeV/c**2 is set for the stop mass, independent of the stop to neutralino mass difference and of the stop lifetime.