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Experimental Determination of the Dalitz-Plot Distribution of the Decays η → π + π − π …

1970; American Physical Society; Volume: 2; Issue: 3 Linguagem: Inglês

10.1103/physrevd.2.501

1538-4500

M. Gormley, E. Hyman, Wonho Lee, T. Nash, J. Peoples, C. Schultz, Stephen J. Stein,

Nuclear physics research studies

We have analyzed the Dalitz-plot distribution of the two dominant charged decays of the $\ensuremath{\eta}$ meson. From 7250 examples of $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\gamma}$, we find that the $\ensuremath{\gamma}$-ray energy spectrum disagrees with the simplest gauge-invariant matrix element corresponding to the dipion in the $J=1$ state. However, it agrees well with a simple $\ensuremath{\rho}$-dominant model. The ${\ensuremath{\pi}}^{0}$ energy spectrum of 30 000 examples of $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ was fitted to a power-series expansion of the matrix element in the usual Dalitz coordinates. We find that a matrix element linear in the ${\ensuremath{\pi}}^{0}$ kinetic energy does not fit our data. We measure the branching ratio $\frac{\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\gamma}}{\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}}$ to be 0.201\ifmmode\pm\else\textpm\fi{}0.006.