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

Abstract

We study the possible interpretation of the two exotic resonances J PC =1 −+ at 1400 and 1600 MeV, claimed to be observed by BNL, decaying, respectively, into ηπ, η′ π, f 1 π and ρπ. These objects are interpreted as hybrid mesons, in the quark–gluon constituent model using a chromoharmonic confining potential. The quantum numbers J PC I G =1 −+1 − can be considered in a constituent model as an hybrid meson ( q q ̄ g ). The lowest J PC =1 −+ states may be built in two ways: l g =1 (gluon-excited) corresponding to an angular momentum between the gluon and ( q q ̄ ) system, while l q q ̄ =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 b 1 π 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.