Suggestion for measuring the weak dipole moment of $τ$ lepton at Z-factory

Abstract

Three new observables for Z-factory to measure the weak dipole moment of $τ$ lepton ($d_w^τ$) are proposed. As those observables employed at LEP-I, the new observables depend on the real and imaginary parts of $d_w^τ$ linearly, thus we calculate the slopes, i.e. the linear coefficients of the dependence, precisely and find that the obtained slopes are much lager than those employed at LEP-I. It means that the signal for the weak dipole moment $d_w^τ$ may be enhanced quite a lot, if one employs the new observables. Being superior to those at LEP-I, we recommend measuring the weak dipole moment $d_w^τ$ in terms of the new observables if re-analyzing the data of LEP-I or doing the measurement at a possible Z-factory in the near future.