Search for anomalous weak dipole moments of the \(\tau\) lepton

  • The ALEPH Collaboration
experimental physics


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 \(\vert{\rm Im} d_{\tau} \vert < 2.01 \times 10^{-3}\).


Dipole Moment Electric Dipole Magnetic Dipole Differential Cross Section Differential Cross 
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  • The ALEPH Collaboration

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