Search for the decay $\tau^- \to 4\pi^-3\pi^+(\pi^0)\nu_{\tau}

A search for the decay of the tau lepton to seven charged pions and one or zero pizero mesons was performed using the BaBar detector at the PEP-II asymmetric-energy e+e- collider. The analysis uses 232.2 fb-1 of data at center-of-mass energies on or near the Y(4S) resonance. We observe 24 events with an expected background of 21.6+-1.3 events. Without evidence for a signal, we calculate an upper limit of BR(tau- --> 4pi- 3pi+ (pizero) nu_tau) < 3.0*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- --> 4pi- 3pi+ nu_tau and tau- --> 4pi- 3pi+ pizero nu_tau.