Evidence is presented for zeros in the $\pi$-exchange contribution to ${\rho }^0{\Delta }^{++}$ and in the $\rho$-exchange contribution to ${\omega }^0{\Delta }^{++}$ production. The position of the $\pi$-exchange zero is consistent with a $\pi$ trajectory with ${{\alpha }_{\pi }}^{\prime }\mathrm{}\left(0\right)\mathrm{}\approx 1.2 {\left(\frac{\mathrm{GeV}}{c}\right)}^{-2\mathrm{}}$. Evidence is also presented suggesting that the $A_2$ chooses the Gell-Mann mechanism (nonsense choosing). A model of $\pi$ exchange with exact $\pi -B$ exchange degeneracy is found to describe the data quantitatively.

• Received 8 June 1970

DOI:https://doi.org/10.1103/PhysRevLett.25.617