Diffractive and Coulomb dissociation of pions into three-pion final states at low momentum transfer

This paper presents an analysis of $\pi^{-}Pb\rightarrow$ $X^{-}Pb\rightarrow\pi^{-}\pi^{-}\pi^{+}Pb$ events at 190GeV$/c$ beam momentum and low four-momentum transfer $t′ <$ 0.01 (GeV$/c$)$^{2}$. Coherent scattering off the lead nucleus as a whole dominates with contributions from Reggeon, Pomeron and photon exchange. Photoproduction becomes apparent at lowest $t′$ and can be extracted statistically as well as by a partial-wave analysis, indicating also the overlap of diffractive and photo-production of the 3$\pi$ events.