The COMPASS collaboration at CERN has investigated the pi^- gamma -> pi^- pi^- pi^+ reaction at center-of-momentum energy below five pion masses, sqrt(s) < 5 m(pi), embedded in the Primakoff reaction of 190 GeV pions impinging on a lead target. Excha
nge of quasi-real photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, t < 0.001 (GeV/c)^2. Using partial-wave analysis techniques, the scattering intensity of Coulomb production described in terms of chiral dynamics and its dependence on the 3pi-invariant mass m(3pi) = sqrt(s) were extracted. The absolute cross section was determined in seven bins of $sqrt{s}$ with an overall precision of 20%. At leading order, the result is found to be in good agreement with the prediction of chiral perturbation theory over the whole energy range investigated.
