Excluding light gluinos from Z decays

We reanalyze the constraints on light gluinos (mg less than or equal to 5 GeV/c(2)) from the hadronic Z decays into four jets. We find that the published OPAL data from the 1991 and 1992 runs exclude a light quasi-stable gluino with mass less than or similar to 1.5 GeV/c(2) at more than 90% confidence level. This limit depends little on assumptions about the gluino fragmentation and the definition of the gluino mass. The exclusion confidence level is shown as a function of the mass. A future projection is briefly discussed. We also discuss quantitatively how the distributions in the Bengtsson-Zerwas and the modified Nachtmann-Reiter angles change due to the finite bottom quark or gluino mass. The analysis is limited to the leading-order calculations. We, however, give an empirical reason to why the next-to-leading-order corrections are unlikely to change our conclusions. (C) 1997 Published by Elsevier Science B.V.