Strange Baryon Production in Electron-Positron Annihilation

Available from UMI in association with The British Library. Requires signed TDF. This thesis presents a study of strange baryon production, which was made using data collected with the TASSO detector, at the PETRA e^+ e^ - collider. Inclusive cross-sections have been obtained for Lambda^0 and Xi^- production, and upper limits have been placed upon the production rates of Omega^- and Sigma* ^{+/-}(1385). In order to identify a type of particle whose cross-sections one wishes to measure, it has been conventional to apply a series of cuts to those properties of the particle which best distinguish it from the background. In the past, the process by which people have attempted to find a good set of cuts, has relied upon little more than a mixture of intelligent guesswork and trial and error. For the analyses described in this thesis however, a novel approach has been developed to this problem. It was noted that the problem is basically just the mathematical one of maximizing a function (the signal to noise ratio) of a number of unknowns (the cuts), subject to a constraint (that the probability of the particle passing the cuts should exceed some desired value). It could therefore be solved using one of the many optimization routines which are now available. In practice, a program called MINUIT was used. The physical information required for this optimization was obtained from a set of Monte Carlo events. This new approach is not only more aesthetically pleasing than the old one, but it has also allowed more information to be extracted from the available data than was previously possible. The Lambda^0 multiplicity per event is found to be 0.218_sp{ -0.011}{+0.011} +/- 0.021 and 0.256_sp{-0.029} {+0.030} +/- 0.025 at sqrt{s} = 34.8 and 42.1 GeV respectively. The Xi^- multiplicity per event is found to be 0.0111_sp {-0.0027}{+0.0030} +/- 0.0022 at sqrt{s} = 34.8 GeV. Differential cross-sections for Lambda^0 and Xi^ - production are obtained. A study of events containing two Lambda^0's is presented and it is shown that 0.052_sp{-0.012 }{+0.013} +/- 0.012 Lambda^0overline{ Lambda^0} pairs and 0.0052 _sp{-0.0052}{+0.0087} +/- 0.012 Lambda^0 Lambda^0 + overline{ Lambda^0}overline{Lambda ^0} pairs are produced per event at sqrt{s} = 34.8 GeV. In 71_sp{-11}{+11}% of the Lambda^0overline{ Lambda^0} pairs, both particles go into the same hemisphere (taken with respect to the sphericity axis). It is found that the Lambda^0 multiplicity rises as a function of event sphericity, and does so slightly faster than the total charged multiplicity. Upper limits are placed upon the number of Omega^- and Sigma* ^{+/-} (1385) produced per event, of 0.013 and 0.053 respectively, both at 95% confidence level. It is noted that the term "upper limit" is not uniquely defined, and for this reason both upper limits are calculated using three of the most common definitions of the term. The results are then compared.