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Zeitschrift für Physik C
ISSN: 0170-9739 (printed version)
ISSN: 1431-5858 (electronic version)
Abstract Volume 74 Issue 3 (1997) pp 403-412
Search for CP violation in Z$^0\longrightarrow{\tau^+\tau^-}$ and an upper limit on the weak dipole moment of the $\tau$ lepton
K. Ackerstaff et al. (8)OPAL Collaboration
(8) CERN, European Organisation for Particle Physics, CH-1211 Geneva 23, Switzerland
Received: 12 December 1996
Abstract. An improved test of ${\cal CP}$ invariance in the reaction ${\rm e^+e^-} \rightarrow \tau^+ \tau^-$ on the ${\mathrm Z^0}$ peak is performed using the data sample recorded between 1991 and 1995 with the OPAL detector at LEP. Optimal observables, requiring the reconstruction of the $\tau$ flight direction and spin, have been used for different final state topologies. From the non-observation of ${\cal CP}$ violation we derive 95% confidence level upper limits on the real and imaginary parts of the weak dipole moment of the $\tau$ lepton of $|{\mathrm Re}(d^{w}_\tau(m_Z^2))| < 5.6 \times 10^{-18} e$ cm and $|{\mathrm Im}(d^{w}_\tau(m_Z^2))| < 1.5 \times 10^{-17} e$ cm, respectively.
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