Charmonium Spectrum from Quenched QCD with Overlap Fermions
  We present the first study of the charmonium spectrum using overlap fermions, on quenched configurations. Simulations are performed on $16^3 \times 72$ lattices, with Wilson gauge action at $\beta$ = 6.3345. We demonstrate that we have discretization errors under control at about 5%. We obtain 88(4) MeV for hyperfine splitting using the $r_0$ scale, and 121(6) MeV using the ($1\bar{P}-1\bar{S}$) scale. This paper raises the possibility that the discrepancy between the lattice results and the experimental value for charmonium hyperfine splitting can be resolved using overlap fermions to simulate the charm quark on lattice. 
S. Tamhankar, A. Alexandru, Y. Chen, S.J. Dong, T. Draper, I. Horvath,   F.X. Lee, K.F. Liu, N. Mathur and J.B. Zhang (chiQC...