First QCD results from SLD

k .. The first Z” data were recorded by the SLD experiment at SLAC during an engineering run in 1991’. From the sample of a few hundred hadronic events collected, the strong coupling cr,(Mz) has been measured from jet rates and energy-energy correlations -(EEC). These (p re iminary) 1 results are presented here. From jet rates a second order perturbative QCDfit yields: a,(Mz) = 0.117 f 0.009 (stat.) f 0.006 (exp. syst.) ‘8*$; (theory). Large systematic differences between cyb values derived from fits to the EEC distribution are observed for various second order QCD calculations, in addition-to a significant dependence on the QCD renormalisation scale ~1~. For the Kunszt-Nason calculations at p2 = 0.1, ty#(Mz) = 0.123 f 0.004 (stat.) ~$~~ (exp. syst.) ‘i:$i (theory) is obtained. For both measurements the theoretical error is dominated by the uncertainty involved in choosing the scale p2. . Presented at the XXVII Rencontre de Moriond: &CD and High Energy Hadronic Interactions . Les Arcs, Prance, March 22-28, 1992 * Work supported by Department of Energy contracts DE-AC03-76SF00515 (SLAC), and DE-AC02-76ER03069 (MIT).