The polarization parameter $P\left(t\right)\mathrm{}$ for the reaction ${\pi }^{-}p\to {\pi }^{0}n$ has been measured at 3.5 and 5.0 GeV/c over the range $0.2<~-t<~1.8$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. The two $\gamma$ rays from the ${\pi }^0$ decay were detected in a large lead-glass hodoscope. The results agree with the positive polarization values found in earlier Argonne National Laboratory data at $-t<\mathrm{}0.35\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. $P\left(t\right)\mathrm{}$ drops to a small value near $t=-0.6\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ and remains the same out to $t=-1.8\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$.

• Received 20 November 1972

DOI:https://doi.org/10.1103/PhysRevLett.30.239