Colour octet contribution to exclusive P-wave charmonium decay into nucleon-antinucleon

We show that although there is no infrared divergence in exclusive P-wave quarkonium decays, the colour octet contribution is no less important than in the inclusive decay. Results from more proper calculations with only colour singlet contribution are not sufficient to account for the measured partial decay widths and so the next higher Fock state must be included. Using the \c_J decay into $N\bar N$ as an example, a scheme is devised to yield estimates of the decay widths using both contributions, the results are comparable with experimental measurements.