Interpretations for the X(4160) observed in the double charm production at B factories

Understand

Belle Collaboration has recently observed a new state, the X(4160), in the process of double charm production $e^+e^-\to J/\psi+X(4160)$ followed by $X(4160)\to D^*\bar{D^*}$.

• We discuss possible interpretations for the X(4160) based on the NRQCD calculations and the potential model estimates for the charmonium spectrum.
• We first focus on the D-wave spin-singlet $2^{-+}$ charmonium $^1D_2(2D)$, which is estimated to have a small production rate of about 5% of that for $e^+e^-\to J/\psi+\eta_c(1S)$, and therefore is incompatible with the observed data for X(4160).
• We then discuss the possibility that the X(4160) is the known $J^{PC}=1^{--}$ charmonium state $\psi(4160)$, which can be produced via two photon fragmentation, but the production rate is much smaller than observed for $e^+e^-\to J/\psi+X(4160)$.