The VES experiment has collected high statistics of exclusive reactions with three pions in the final state:
π−π−π+ (about 43⋅106 events) and π−π0π0 (about 20⋅106 events).
The 3π systems are produced by impinging of 28.9 GeV π− beam on the beryllium target.
The dominant production mechanism is the Pomeron exchange between incoming beam pion and the target.
At the very low momentum transfer squared t′ the data clearly shows coherent diffractive production
on the whole nucleus which is replaced by incoherent process on the individual nucleons at higher 0.05<t′<1GeV2.
The mass-independent partial wave analysis is performed dividing data into
the bins of m(3π) and t′.
The comparison of results with two models of PWA: using formalism of unlimited-rank density matrix
and, using rank=1 is presented.
The predicted isospin relations (assuming I=1 of 3π systems) and observed ones for
intensities in π−π−π+ and π−π0π0 are shown.