Thep - bar p decays ofP-wave quarkonium and the helicity characteristics of massless QCD

We consider the exclusive (p - bar p) decays of the quarkoniumP-states. Due to the helicity conservation of massless QCD the (p - bar p) mode is forbidden in this limit for the¹ P ₁ and the³ P ₀ states. The angular distributions for the decays of the remaining states in the cascade (^3 Sprime _1 to gamma ^3 P_J to gamma pbar p) are specific to QCD and can serve as a test of the theory. The same is true of the formation process (pbar p to ^3 P_J to ^3 S_1 gamma ) . In lowest order QCD we obtain overall branching ratios for charmonium of the order of 10^?4.