New analysis of ηπ tensor resonances measured at the COMPASS experiment

Abstract We present a new amplitude analysis of the ηπ D -wave in the reaction π − p → η π − p measured by COMPASS. Employing an analytical model based on the principles of the relativistic S -matrix, we find two resonances that can be identified with the a 2 ( 1320 ) and the excited a 2 ′ ( 1700 ) , and perform a comprehensive analysis of their pole positions. For the mass and width of the a 2 we find M = ( 1307 ± 1 ± 6 ) MeV and Γ = ( 112 ± 1 ± 8 ) MeV, and for the excited state a 2 ′ we obtain M = ( 1720 ± 10 ± 60 ) MeV and Γ = ( 280 ± 10 ± 70 ) MeV, respectively.