Orbital-Angular-Momentum Structure of theA1Meson

The orbital angular momentum of the ${A}_{1}$ meson produced from ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}p$ at 16 GeV/c was studied by analyzing the decay angular distributions in the ${\ensuremath{\rho}}^{0}{\ensuremath{\pi}}^{\ensuremath{-}}$ state. A completely Bose-symmetrized formalism was used to measure the ratio $\frac{{g}_{1}}{{g}_{0}}$ of the helicity states of the $\ensuremath{\rho}$ from the ${A}_{1}$ decay. The value obtained, $|\frac{{g}_{1}}{{g}_{0}}|=0.48\ifmmode\pm\else\textpm\fi{}0.13$, indicates a substantial $d$-wave contribution in the ${A}_{1}$ decay.