Study of the ηπ− system in the π-p reaction at 6.3 GeV/c

Data of the ηπ− system were obtained in the reaction π−p → ηπ−p at 6.3 GeV/c beam momentum. About 17 k events of ηπ− were collected in the mass range 0.8 ⩽ Mηπ- ⩽ 1.8 GeV/c2 and in the range of the momentum transfer squared 0.075 ⩽ |t′| ⩽ 0.60 (GeV/c)2. A large forward-backward asymmetry was observed around 1.3 GeV/c2 in the Gottfried-Jackson frame of the ηπ− system. A partial wave analysis of the data was performed. A peak of the D+ wave attributed to a2 (1320) is clearly seen. An enhancement is observed around 1.3 GeV/c2 in the P+ wave.