The reaction ${\gamma }_{\perp ,\parallel }p\to {\pi }^{+}n$ has been studied with linearly polarized photons of energy 3.0 GeV at $-t$ values between 0.15 and 1.2 ${\left(\frac{\mathrm{GeV}}{c}\right)}^2$. The asymmetry $A^{+}=\frac{(d{\sigma }_{\perp }-d{\sigma }_{\parallel })}{(d{\sigma }_{\perp }+d{\sigma }_{\parallel })}$ is found to be positive throughout this four-momentum-transfer range, implying the dominance of natural parity exchange in the $t$ channel. Comparison of $d{\sigma }_{\perp }({\gamma }_{\perp }p\to {\pi }^{+}n)$ and $d{\sigma }_{\perp }p\to {\pi }^{-}p$) from a previous experiment indicates strong interference between the isoscalar and isovector photon amplitudes for photons polarized perpendicular to the production plane.

• Received 11 August 1970

DOI:https://doi.org/10.1103/PhysRevLett.25.1053