Search for charginos nearly mass degenerate with the lightest neutralino in e(+)e(-) collisions at centre-of-mass energies up to 209 GeV

A search for charginosnearly mass degenerate with the lightest neutralinois performed with the data collected by the ALEPHdetector at LEP, at centre-of-mass energies between 189 and 209 GeV, corresponding to an integrated luminosity of 628 pb(-1). The analysis is based on the detection of isolated and energetic initial state radiation photons, produced in association with charginopairs whose decay productshave little visible energy. The number of candidate events observed is in agreement with that expected from Standard Model background sources. These results are combined with those of other direct searches for charginos, and a lower limit of 88 GeV/c(2) at 95% confidence level is derived for the charginomass in the case of heavy sfermions, irrespective of the chargino- neutralinomass difference. (C) 2002 Elsevier Science B.V. All rights reserved.