Measurement of the $\tau$-lepton lifetime at Belle

The lifetime of the $\tau$-lepton is measured using the process $e^{+}{e}^{-}\to {\tau }^{+}{\tau }^{-}$, where both $\tau$-leptons decay to $3\pi {\nu }_{\tau }$. The result for the mean lifetime, based on $711{\mathrm{f}\mathrm{b}}^{-1}$ of data collected with the Belle detector at the $\mathrm{{\rm Y}}(4S)$ resonance and $60\mathrm{M}\mathrm{e}\mathrm{V}$ below, is $\tau = (290.17 \pm 0.53($\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.}$) \pm 0.33($\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}$))\cdot10^{-15},$\mathrm{s}$$. The first measurement of the lifetime difference between ${\tau }^{+}$ and ${\tau }^{-}$ is performed. The upper limit on the relative lifetime difference between positive and negative $\tau$-leptons is $\mathrm{\mid }\mathrm{\Delta }\tau \mathrm{\mid }\mathrm{/}\tau <7.0\times {10}^{-3}$ at 90% CL.