Higher twist effect in inclusive quarkonium photoproduction

We analyze the higher twist effect in photoproduction of the quarkonium, where the quarkonium is a spin-triplet, S-wave state. We find that the non-perturbative effect of the next-to-leading twist is contained in three correlation functions related to the initial hadron and some of the effect of the next-to-leading twist is only suppressed by the inverse of the mass square of the quarkonium. A naive estimate indicates that the effect can be significant for charmonium. In the analysis we only take the leading order in the small velocity expansion for the non-perturbative parts related to the quarkonium. Possible corrections from higher orders, especially corrections from color-octet states, are discussed in detail. (orig.)