No abstract

A search for a supersymmetric partner of the top quark (t 1 ) has been performed by the OPAL experiment i n e + e collisions at LEP. The integrated luminosity of the data sample analysed was 69.1 pb 1 , which corresponds to 1.6810 6 produced Z 0 ! q q e v ents. Not 1 candidates have been found. This study excludes the existence of thet 1 with a mass below 45.1 GeV at 95% C.L., where the mixing angle of left-and right-handed partners is smaller than 0.85 rad or greater than 1.15 rad, and the mass dierence between thet 1 and the lightest neutralino is greater than 5 GeV.

No abstract

The strong coupling constant, s , has been determined in hadronic decays of the Z 0 resonance, using measurements of seven observables relating to global event shapes, energy correlations and jet rates. The data have been compared with resummed QCD calculations, which are combined with the O(2 s) theory. The seven measurements agree to about 10%, and the nal result, based on a weighted average, is: s (M Z 0) = 0 : 120 0:006 ; where the error includes both experimental and theoretical uncertainties. This value corresponds to renormalization scale = M Z 0 and the error includes the uncertainty in this choice of scale. The present measurement complements previous determinations using the O(2 s) QCD matrix elements alone, and yields a compatible result, with comparable errors.