The experimental data on the $3\pi$ decay of $\tau$ mesons is summarized on a convenient two-dimensional plot, both (a) when the $\pi$-meson charges are known and (b) when they are not. Some events may be included in plot (a) only if the parent $\tau$ meson is assumed positive and arguments supporting this identification for $\tau$ mesons decaying in an emulsion are discussed. The dependence of this plot on the $\tau$-meson spin ($j$) and parity ($w$) is discussed in general terms and those features depending particularly on $w$ and on its relation with $j$ are emphasized—for example, if the density of events does not vanish at the bottom of the plot, the $\tau$ meson must have odd parity and even spin. Simple estimates of the distribution, using only the lowest allowable angular momenta and a "short range" approximation, may be modified by final-state meson-meson attractions, whose effects are discussed qualitatively. The available data are insufficient for any strong conclusion to be drawn but rather suggest even spin and odd parity for the $\tau$ meson; the need for careful assessment of geometrical bias in the selection of experimental material is stressed.

• Received 9 February 1954

DOI:https://doi.org/10.1103/PhysRev.94.1046