The decay of the observed JPC=1−+ (1400) and JPC=1−+ (1600) hybrid candidates

We study the possible interpretation of the two exotic resonances JPC=1−+ at 1400 and 1600 MeV, claimed to be observed by BNL, decaying, respectively, into ηπ, η′π, f1π and ρπ. These objects are interpreted as hybrid mesons, in the quark–gluon constituent model using a chromoharmonic confining potential. The quantum numbers JPCIG=1−+1− can be considered in a constituent model as an hybrid meson (qq̄g). The lowest JPC=1−+ states may be built in two ways: lg=1 (gluon-excited) corresponding to an angular momentum between the gluon and (qq̄) system, while lqq̄=1 (quarks-excited) corresponds to an angular momentum between q and q̄. For the gluon-excited mode 1−+ hybrids, we find the decay dominated by the b1π channel, and by the ρπ channel for the quark-excited mode. In our model, neither the quark-excited nor the gluon-excited 1−+ (1400 MeV) hybrids can decay into ηπ and η′π, in contradiction with experiment. Hence, the 1400 MeV resonance seems unlikely to be an hybrid state. The 1−+ (1600 MeV) gluon-excited hybrid is predicted with too large a total decay width, to be considered as an hybrid candidate. On the contrary the quark-excited mode has a total decay width around 165 MeV, with a ρπ preferred decay channel, in agreement with BNL. Our conclusion is that this resonance may be considered as a hybrid meson in the quark-excited mode.