Bound on the tau neutrino magnetic moment from the TRISTAN experiments

Abstract

We set limits on the magnetic moment and charge radius of the tau neutrino by examining an extra contribution to the electroweak process $e^+ e^- \to \nu \bar{\nu}\gamma$ using VENUS, TOPAZ and AMY results. We find that $\kappa(\nu_{\tau}) < 9.1\times{10}^{-6}$ (i.e. $\mu(\nu_{\tau}) < 9.1\times{10}^{-6}\mu_B, \mu_B = e/2m_e$) and $<r^2 > < 3.1\times{10}^{-31}$cm$^2$ with Poisson statistics by combining their results. Whereas, similar to this method, with the Unified Approach we find that $\kappa(\nu_{\tau}) < 8.0\times{10}^{-6}$ and $<r^2 > < 2.7\times{10}^{-31}$cm$^2$.