Exotic meson production in the f1(1285)π− system observed in the reaction π−p→ηπ+π−π−p at 18 GeV/c

Abstract This Letter reports results from the partial wave analysis of the π − π − π + η final state in π − p collisions at 18 GeV /c . Strong evidence is observed for production of two mesons with exotic quantum numbers of spin, parity and charge conjugation, J PC =1 −+ in the decay channel f 1 (1285) π − . The mass M=1709±24±41 MeV /c 2 and width Γ=403±80±115 MeV /c 2 of the first state are consistent with the parameters of the previously observed π 1 (1600). The second resonance with mass M=2001±30±92 MeV /c 2 and width Γ=333±52±49 MeV /c 2 agrees very well with predictions from theoretical models. In addition, the presence of π 2 (1900) is confirmed with mass M=2003±88±148 MeV /c 2 and width Γ=306±132±121 MeV /c 2 and a new state, a 1 (2096), is observed with mass M=2096±17±121 MeV /c 2 and width Γ=451±41±81 MeV /c 2 . The decay properties of these last two states are consistent with flux tube model predictions for hybrid mesons with non-exotic quantum numbers.