New Determination of the Dalitz-Plot Distribution forτ−Decays

Abstract

We have measured the $X$ and $Y$ projections of the Dalitz plot of 81000 ${\ensuremath{\tau}}^{\ensuremath{-}}$ decays. The decays were observed in a beam of 400-MeV/c ${K}^{\ensuremath{-}}'\mathrm{s}$ 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 $(\mathrm{phase}\mathrm{space})\ifmmode\times\else\texttimes\fi{}(1+AY)$ and have determined for $A$ the values 0.252 \ifmmode\pm\else\textpm\fi{} 0.011 with Coulomb corrections to the distribution, 0.219\ifmmode\pm\else\textpm\fi{}0.011 without Coulomb corrections. The results have been obtained using a method which involves measured rather than fitted quantities.