π+ Energy spectrum and branching ratio of the τ′ decay

A total of 2027 K+→π+π0π0 decays at rest were analysed in hydrogen and heavy liquid bubble chambers. The π+ energy spectrum is compared with 3 spectrum shapes:a) linear matrix element,b) linear spectrum, andc) σ resonance hypothesis. The comparison between τ′ and τ decays indicates that they are consistent withI=1 final state and that the agreement is better if one uses the linear matrix element fit in the τ′ decay. Our data fit also well the σ resonance hypothesis formσ∼350 MeV and Γσ∼80 MeV, but do not allow a definite conclusion on this point. The τ′ to τ branching ratio obtained is 0.303±0.009.