Y(4260) on the lattice

We investigate the mass spectra of the hybrid charmonium $ \cbar \c{g} $, the molecules $ (\cbar \c)^* (\qbar \q) $ and $ (\qbar \c)^* (\cbar \q) $, and the diquark-antidiquark $ [\q\c]^*[\qbar\cbar] $ with $J^{PC}=1^{--}$, in quenched lattice QCD with exact chiral symmetry. For two lattice volumes $ 24^3 \times 48 $ and $ 20^3 \times 40 $, each of 100 gauge configurations generated with single-plaquette action at $ \beta = 6.1 $, we compute point-to-point quark propagators and measure the time-correlation functions of above candidates for $ Y(4260) $. Our results suggest that $ Y(4260) $ is unlikely to be identified with the hybrid charmonium $ \cbar \c{g} $, but its mass is compatible with the 4-quark state $[\q^T C\gamma_5\gamma_i \c][\qbar C\gamma_5 \cbar^T] $ as well as the molecule $(\qbar\gamma_i\c)(\cbar\q) $. Further, we predict the existence of the "double-charmonium" $ (\c\c\cbar\cbar) $ around $ 6400 \pm 50 $ MeV with $ J^{PC} = 1^{--} $.