Diffractive and Nondiffractive $A_1$, $A_3$, and $A_4$ Production in ${\pi }^{+}p$ Interactions at 15 GeV/c

We have studied the spin-parity structure of the $3\pi$ system produced opposite a proton or ${\Delta }^{++}$ in ${\pi }^{+}p$ interactions at 15 GeV/c. Our results suggest that the broad enhancement at 1.1 GeV, traditionally associated with the $A_1$, does not have the properties usually associated with a resonant state. We obtain similar results for the $A_3$ and $A_4$ enhancements.