The COMPASS Collaboration at CERN has investigated the reaction $pi^- gamma rightarrow pi^-pi^-pi^+$ embedded in the Primakoff reaction of $190~textrm{GeV}$ pions scattering in the Coulomb field of a lead target, $pi^- text{Pb} rightarrow pi^-pi^-pi^+ text{Pb}$. Exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at momentum transfer below $0.001~(text{GeV}/c)^2$. Using a partial-wave analysis the amplitudes and relative phases of the $a_2(1320)$ and $pi_2(1670)$ mesons have been extracted, and the Coulomb and the diffractive contributions have been disentangled. Measuring absolute production cross sections we have determined the radiative width of the $a_2(1320)$ to be $Gamma_0(a_2(1320) rightarrow pigamma) = (358 pm 6_{textrm{stat}} pm 42_{textrm{syst}})~textrm{keV}$. As the first measurement, $Gamma_0(pi_2(1670) rightarrow pigamma) = (181 pm 11_{textrm{stat}} pm 27_{textrm{syst}})~textrm{keV} cdot (textrm{BR}^{textrm{PDG}}_{f_2 pi}/textrm{BR}_{f_2 pi})$ is obtained for the radiative width of the $pi_2(1670)$, where in this analysis the branching ratio $textrm{BR}^{textrm{PDG}}_{f_2 pi}=0.56$ has been used. We compare these values to previous measurements and theoretical predictions.
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