Measurements of tau decays to three pions

Abstract We reports the result of a study of a tau decays with three pions in the final state ( τ ± → π ± π + π − υ τ and τ ± → π ± π 0 π 0 υ τ ) from data accumulated with the MAC detector operating at the PEP storage ring. The branching fractions for these modes are measured to be 0.070±0.003±0.007 and, with assumptions discussed in the text, 0.087±0.004±0.011, respectively. Assuming that these final states result from the decay of the a 1 meson, we measure the resonant parameters of the a 1 with the three charged pion sample to be m a1 =1166±18±11 MeV and γ a1 =405±75±25 MeV, and with the one charged plus two neutral pions sample to be m a1 =1164±41±23 MeV and γ a1 =419±108±57 MeV.