Coherent Pion Dissociation into Three Pions on Nuclear Targets

A partial-wave decomposition has been made of the final-state $3\pi$ system produced in the reaction ${\pi }^{-}+A\to \left({\pi }^{-}{\pi }^{-}{\pi }^{+}\right)+A$ at 23 GeV/c and for the elements C, Al, Cu, and Ag. For low $3\pi$ masses, the $1^{+}$ state is dominant and its $t^{\prime }$ distribution shows the expected combination of coherent and incoherent components. The $t^{\prime }$ distribution of the $2^{+}$ $A_2$ state also requires both coherent and incoherent components.