The data collected at a centre-of-mass energy of 188.6 GeV by ALEPH at LEP,
corresponding to an integrated luminosity of 173.6 pb(-1), are analysed in
a search for the scalar partners of quarks and leptons predicted in supers
ymmetric models. No evidence for any such particles was found in the decay
channels (l) over tilde --> l chi, (t) over tilde --> bl<(nu)over tilde>, (
b) over tilde --> b chi, and (q) over tilde --> q chi. Improved mass lower
limits have been obtained in the framework of the Minimal Supersymmetric St
andard Model. (C) 1999 Published by Elsevier Science B.V. All rights reserv
ed.