Search for the decayτ−→4π−3π+(π0)ντ

A search for the decay of the $\tau$ lepton to seven charged pions and one or zero ${\pi }^0$ mesons was performed using the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider. The analysis uses $232.2{\mathrm{fb}}^{-1}$ of data at center-of-mass energies on or near the ${\rm Y}(4S)$ resonance. We observe 24 events with an expected background of $21.6\pm 1.3$ events. Without evidence for a signal, we calculate an upper limit of $\mathcal{B}$ $({\tau }^{-}\to 4{\pi }^{-}3{\pi }^{+}({\pi }^0){\nu }_{\tau })<3.0\times {10}^{-7}$ at 90% confidence level. This is an improvement by nearly an order of magnitude over the previously established limit. In addition, we set upper limits for the exclusive decays ${\tau }^{-}\to 4{\pi }^{-}3{\pi }^{+}{\nu }_{\tau }$ and ${\tau }^{-}\to 4{\pi }^{-}3{\pi }^{+}{\pi }^0{\nu }_{\tau }$.