Total hadronic cross section in electron-positron annihilation at center-of-mass energies from 50 to 57 GeV

Thesis (Ph. D.)--University of Rochester. Dept. of Physics and Astronomy, 1989.An analysis of electron-positron annihilation into hadronic final states at center-of-mass energies ranging from 50 to 57 GeV, measured by the AMY detector at the TRISTAN e+e-collider, is presented. With a data sample corresponding to an integrated luminosity of 19.3 pb-1 , a total of 2280 hadronic events were selected. The total cross sections (or the ratios R) were then determined with an overall normalization error of 4.1% and point-to-point systematic errors ranging from 1.1% to 2.8%. We observed an evident rise in R that is due to the Zo intermediate state. Although the measured total cross sections at the higher energies tend to be consistently larger than the prediction of the standard model using the nominal values for Mzo, sin² Θw, and [sic]MS they are still consistent. Event shape variables were calculated to further test for the possibility of new heavy quark production. They are all consistent with expectations based on five quark flavors. Assuming a threshold dependence as given by the quark-parton model, 95% confidence level lower mass limits of mt > 27.6 GeV/c² for the top quark and mb > 25.5 GeV/c² for the fourth generation down quark were obtained. Our R values together with lower energy results were compared to the standard model prediction to obtain best fit values for the standard model parameters Mzo, the Zo boson mass, and [sic]MS, the QCD scale parameter. The fits yielded Mzo = 88.8 ± 2.0 GeV/c² and [sic]MS = O.17 +0.15/-0.11 GeV with the third-order QCD corrections. The value of Mzo, although somewhat smaller, is still marginally consistent with the direct measurement of Mzo. In the determination of [sic]MS, the effects of the third-order QCD corrections are found to be significant