A measurement of the forward-backward asymmetry of$e^ + e^ - \to c\bar c$ and$e^ + e^ - \to b\bar b$ at centre of mass energies on and near theZ ⁰ peak usingD ^*± mesons

Abstract

A measurement is presented of the forwardbackward asymmetry of the processes$e^ + e^ + \to c\bar c$ and$e^ + e^ + \to b\bar b$ at centre of mass energies near 91 GeV. Decays of theZ ⁰ into charm and bottom quarks are identified using 6507 chargedD ^* mesons, reconstructed in the decaysD ^*±→D ⁰ π ^±→(K ^∓ π ^±)π ^±,D ^*±→D ⁰ π ^±→(K ^∓ π ^± π ⁰)π ^± andD ^*±→D ⁰ π ^±→(K ^∓ π ^± π ^∓ π ^±)π ^±. Thec quark asymmetry on theZ ⁰ peak is measured to be

$$A_{FB}^c = 0.052 \pm 0.028(stat.) \pm 0.012(sys.).$$

The energy dependence of the asymmetry has been investigated at energies close to theZ ⁰ peak. Consistency with the predictions of the Standard Model is found.

Combining these measurements with the determination of the asymmetries from semileptonic decays, the following results forb andc quarks are found

$$\begin{gathered} A_{FB}^c = 0.032 \pm 0.021(stat.) \pm 0.015(sys.), \hfill \\ A_{FB}^b = 0.096 \pm 0.017(stat.) \pm 0.008(sys.), \hfill \\ \end{gathered} $$

with a correlation coefficient of +0.15.