Orbital-Angular-Momentum Structure of theA1Meson

The orbital angular momentum of the $A_1$ meson produced from ${\pi }^{-}p\to {\pi }^{-}{\pi }^{-}{\pi }^{+}p$ at 16 GeV/c was studied by analyzing the decay angular distributions in the ${\rho }^0{\pi }^{-}$ state. A completely Bose-symmetrized formalism was used to measure the ratio $\frac{g_1}{g_0}$ of the helicity states of the $\rho$ from the $A_1$ decay. The value obtained, $\left|\frac{g_1}{g_0}\right|=0.48\mathrm{}\pm 0.13$, indicates a substantial $d$-wave contribution in the $A_1$ decay.