Quarks-excited states or gluon-excited states, are the J^{PC}=1^{-+} hybrid mesons confirmed?

Abstract

The existence of hadrons containing gluons as constituent particles (like hybrid mesons) will involve the necessity to admit an hadronic spectroscopy beyond the naive quark model. In the QGC model, the lowest J^{PC}= 1^{-+} hybrid mesons may be built in two different modes: the GE-mode corresponding to an angular momentum between the gluon and qqbar system, while the QE-mode corresponding to an angular momentum between q and qbar. In this paper, we give an analysis of the possible 1^{-+} hybrid mesons in the 1.32-2.04 GeV mass range, and predictions on their decay. We discuss on the inconsistency between some theoretical results and experimental data.We find that the 1^{-+}(1400 MeV), dominated by the QE-mode will decay in the favourite rho-pi channel, while the GE-1^{-+}(1600 MeV), and the 1^{-+}(2.0 GeV), pure GE-hybrids, will decay preferably into b1-pi channel (never observed); we indicate problems concerning the observation of decay channels which are forbidden by theoretical present models.The total decay widths of the 1^{-+}(2.0 GeV) and the GE-1^{-+}(1600 MeV) being very large, this leads to a problem of their observability as resonances. We may conclude that at this time, there is no absolute confirmation of their existence, but some asked questions remain not solved.