Production ofρ−in the Nuclear Coulomb Field

The coherent process ${\pi }^{-}+A\to A+{\pi }^{-}+{\pi }^0$ has been measured using nuclear targets. Sharp peaks are observed in the $t^{\prime }$ distributions. The $\pi \pi$ mass spectrum is dominated by the ${\rho }^{-}$ meson produced in the nuclear Coulomb field and by ${\omega }^0$ exchange in the nuclear surface. The Coulombic process yields a measurement of the radiative width, $\Gamma ({\rho }^{-}\to {\pi }^{-}+\gamma )=35\mathrm{}\pm 10$ keV, which is in poor agreement with the simple unbroken-SU(3) prediction of 100 keV.