New determination of the Dalitz-plot distribution for tau- decays

We have measured the X and Y projections of the Dalitz plot of 81000 τ⁻ decays. The decays were observed in a beam of 400-MeV/c K⁻'s in the BNL 30-in. liquid-hydrogen bubble chamber. For the X distribution we find no deviation from phase space. For Y we find a distribution of (phasespace)×(1+AY) and have determined for A the values 0.252 ± 0.011 with Coulomb corrections to the distribution, 0.219±0.011 without Coulomb corrections. The results have been obtained using a method which involves measured rather than fitted quantities.