X(3872) in lattice QCD with exact chiral symmetry

We investigate the mass spectrum of $1^{++}$ exotic mesons with quark content $(\stackrel{¸}{\text{q}}\text{cbar}\text{qbar})$, using molecular and diquark-antidiquark operators, in quenched lattice QCD with exact chiral symmetry. For the molecular operator $ {(\qbar\gamma_i\c)(\cbar\gamma_5\q)- (\cbar\gamma_i\q)(\qbar\gamma_5\c) } $andthediquark-antidiquarkoperator$ {(\q^T C \gi \c)(\qbar C \gamma_5 \cbar^T)-(\qbar C \gi^T \cbar^T)(\q^T C \gamma_5 \c) } $,bothdetectaresonancewithmassaround$ 3890 \pm 30 $ MeV in the limit $m_q\to m_u$, which is naturally identified with $X(3872)$. Further, heavier exotic meson resonance with $J^{PC}=1^{++}$ is also detected, with quark content $(\stackrel{¸}{\text{s}}\text{cbar}\text{sbar})$ around $4100\pm 50$ MeV.