Measurement of the strange quark forward-backward asymmetry around the Z \(^{0}\) peak

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Abstract.

A precise measurement of the strange quark forward-backward asymmetry used 3.2M multihadronic events around the Z \(^0\) peak collected by the DELPHI experiment from 1992 to 1995. The ring imaging Cherenkov detectors in the barrel and end-cap regions identify high energy charged kaons which tag the s quark. The s quark asymmetry was measured at different centre-of-mass energies; in particular at the Z \(^0\) pole

\begin{equation} A^0_{s\bar{s}} = 0.1008 \pm 0.0113 \, \mbox{(stat.)} \pm 0.0040 \, \mbox{(syst.)}, \nonumber \end{equation}

taking the expected d and u quark asymmetries from the Standard Model. The quark flavour fractions are assumed from the Standard Model and the fragmentation process is modelled by JETSET. From the s quark pole asymmetry the electroweak mixing angle was determined:

\begin{equation} \sin^2\theta_{eff}^{lept} = 0.2321 \pm 0.0029.\nonumber \end{equation}

The parity violating coupling of the s quark to the Z was determined to be:

\begin{equation} A_{s} = 0.909 \pm 0.102\, \mbox{(stat.)} \pm 0.036 \mbox{(syst.)}. \nonumber \end{equation}

Received: 8 October 1999 / Revised version: 23 February 2000 / Published online: 18 May 2000