**30**: 291-304

https://doi.org/10.1140/epjc/s2003-01286-1

experimental physics

## Search for anomalous weak dipole moments of the $\tau$ lepton

The anomalous weak dipole moments of the $\tau$ lepton are measured in a data sample collected by ALEPH from 1990 to 1995 corresponding to an integrated luminosity of 155 pb^{-1}. Tau leptons produced in the reaction $e^+ e^- \rightarrow \tau^+ \tau^-$ at energies close to the ${\rm Z}$ mass are studied using their semileptonic decays to $\pi$, $\rho$, $a_1 \rightarrow \pi 2\pi^0$ or $a_1 \rightarrow 3 \pi$. The real and imaginary components of both the anomalous weak magnetic dipole moment and the CP-violating anomalous weak electric dipole moment, $ {\rm Re} \mu_{\tau}$, ${\rm Im} \mu_{\tau}$, ${\rm Re} d_{\tau}$ and ${\rm Im} d_{\tau}$, are measured simultaneously by means of a likelihood fit built from the full differential cross section. No evidence of new physics is found. The following bounds are obtained (95% CL): $\vert{\rm Re} \mu_{\tau} \vert < 1.14 \times 10^{-3}$, $\vert{\rm Im} \mu_{\tau} \vert < 2.65 \times 10^{-3}$, $\vert{\rm Re} d_{\tau} \vert < 0.91 \times 10^{-3}$, and $\vert{\rm Im} d_{\tau} \vert < 2.01 \times 10^{-3}$.

*© Springer-Verlag, 2003*