## LSU Historical Dissertations and Theses

1990

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

#### Department

Physics and Astronomy

Roger R. McNeil

#### Abstract

This dissertation describes the measurement of the forward-backward charge asymmetry, A$\sb{\rm b}$, for e$\sp{+}$e$\sp{-} \to$ bb at TRISTAN by the AMY detector. A measurement of the ratio, R$\sb{\rm b}$, of the cross section for e$\sp{+}$e$\sp{-} \to$ bb to the theoretical QED cross section for e$\sp{+}$e$\sp{-}\ \to\ \mu\sp{+}\mu\sp{-}$ is also obtained. A$\sb{\rm b}$ is an effect of the weak-electromagnetic interference. The measurement of A$\sb{\rm b}$ is therefore a direct test of the standard model electroweak theory. TRISTAN is the only e$\sp{+}$e$\sp{-}$ collider in the world to explore the center-of-mass energy region of 50 GeV to 62 GeV, where the effects of weak-electromagnetic interference becomes maximum. The data were collected between June 1987 and July 1989 with a total integrated luminosity of 33.3 pb$\sp{-1}$ and center-of-mass energies ranging from 52 GeV to 61.8 GeV. Multihadronic events with a muon were used for the analysis. The measured values were A$\sb{\rm b}$ = $-$0.82 $\pm$ 0.25(stat) $\pm$ 0.14(syst) and R$\sb{\rm b}$ = 0.47 $\pm$ 0.12 $\pm$ 0.12 at an average center-of-mass energy of 57.2 GeV. These results were consistent with the standard model electroweak theory predictions of A$\sb{\rm b}$ = $-$0.58 and R$\sb{\rm b}$ = 0.56 at this energy. The measurement of the charge asymmetry is used to set a limit on B$\sp0-$B$\sp0$ mixing of $\chi\ <$ 0.20 at the 90% confidence level.

164

COinS