The Possible Interpretations of Y(4260)

Abstract

The recently observed Y(4260) lies far above the decay threshold with a width less than 100 MeV. We argue that it's very difficult to accommodate Y(4260) as a conventional $c\bar c$ radial excitation or a D-wave state. It can't be a hadronic molecule. Its production mechanism and special decay pattern do not favor the glueball interpretation. If Y(4260) is a scalar tetraquark, it must be produced by the I=0 component of the virtual photon. Then the $I=1, I_z=0$ component of the virtual photon should have produced its isovector partner $Y^\prime (4260)$, which may be searched for in the decay channel $\pi^+\pi^-\pi^0 J/\psi$ using exactly the same database from the initial state radiation process. The observation/non-observation of $Y^\prime (4260)$ can easily confirm/reject the tetraquark hypothesis. However, a tetraquark far above threshold can fall apart into $D\bar D, D^\ast\bar D$ very easily. Its not-so-large width and the non-observation of $D\bar D$ mode tend to disfavor the tetraquark hypothesis. Hence the only feasible interpretation is a hybrid charmonium if Y(4260) is {\sl NOT} an experimental artifact. At present, none of the experimental information from BABAR measurement is in conflict with the hybrid charmonium picture.