Study of the five-charged-pion decay of the τ lepton

The branching fractions for the five-charged-particle decays of the τ lepton have been measured in ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$ annihilations using the CLEO II detector at the Cornell Electron Storage Ring. Assuming all charged particles to be pions, the results are B(3${\mathrm{\pi }}^{\mathrm{-}}$2${\mathrm{\pi }}^{+}$≥0 neutrals ${\nu }_{\mathrm{\tau }}$)=(0.097±0.005±0.011)%, B(3${\mathrm{\pi }}^{\mathrm{-}}$2${\mathrm{\pi }}^{+}$ ${\nu }_{\mathrm{\tau }}$)=(0.077±0.005 ±0.009)%, B(3${\mathrm{\pi }}^{\mathrm{-}}$2${\mathrm{\pi }}^{+}$ ${\mathrm{\pi }}^0$ ${\nu }_{\mathrm{\tau }}$)=(0.019±0.004±0.004)%, and B(3${\mathrm{\pi }}^{\mathrm{-}}$2${\mathrm{\pi }}^{+}$2${\mathrm{\pi }}^0$ ${\nu }_{\mathrm{\tau }}$)<0.011% at the 90% C.L. B(3${\mathrm{\pi }}^{\mathrm{-}}$2${\mathrm{\pi }}^{\mathrm{-}}$ ${\mathrm{\pi }}^0$ ${\nu }_{\mathrm{\tau }}$) is measured for the first time by exclusive ${\mathrm{\pi }}^0$ reconstruction. The results are compared with the predictions from the partially conserved-axial-current and conserved-vector-current hypotheses assuming isospin invariance.