P-odd observables at the ${\rm Y}$ peak

Abstract

We study the $\gamma$-Z interference in the process $e^{+}{e}^{-}\to {\rm Y}\to {\tau }^{+}{\tau }^{-}$ as a means to measure the neutral current coupling of the b-quark. The helicity amplitudes are calculated from resonant and background diagrams and the spin density matrix of the final state is discussed. The spin analyzer of the $\tau$'s is illustrated with the decays $\pi \nu$ and $\rho \nu \to (\pi \pi )\nu$. With $10^8{\rm Y}$ a sensitivity to $g_V^b$ of a few per cent could be reachable.

Comments: 29 pages + 3 figures. Submitted to Nucl. Phys B