Extraction of resonance poles with J^PC = 2^-+ from COMPASS data

The COMPASS experiment at CERN has collected 5 x 10⁶ events of diffractive scattering of 190 GeV pions to the three-pion final state. Since around one hundred resonances observed in light-quark sector are coupled to pionic systems, the spin-density matrices from a partial wave analysis are extremely valuable to extract ordinary and, possibly, exotic mesons. The aim of the present analysis is to extract three-pion scattering amplitudes from the mass-dependence of the COMPASS spin-density matrices using analyticity and unitarity constraints. The three-body unitarity problem is very difficult and has not been completely solved. In the approximation of the isobar model, it is reduced to quasi-two-body (ππ-subchannel resonance+pion) unitarity requirements. We invoke a unitarization procedure to incorporate non-resonant long-range production processes via pion exchange, i.e. ''Deck''-like processes. This theoretical framework is applied to the COMPASS data. We discuss resonant pole positions and scattering phase shifts for the mesonic J^PC = 2^-+ sector.