2002/08/28 by J. P. Ma, Ma, J. P., Jia-Sheng Xu +1
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #High Energy Physics - Phenomenology (hep-ph) #hep-ex #hep-ph
paper · pdf · doi:10.48550/arxiv.hep-ph/0208253
Reference updated, typos eliminated, some words changed
arxiv created 2002/10/09 · arxiv updated 2009/11/30
There are different approaches for diffractive photoproduction of charmonia. Recently, a new approach is proposed, in which charm quarks are taken as heavy quarks and the nonperturbative effect related to charmonia can be handled with nonrelativistic QCD. The interaction between the c c pair and the initial hadron is through exchange of soft gluons. The exchange of soft gluons can be studied with heavy quark effective theory and an expansion in the inverse of charm quark mass mc can be employed. In this approach a simple formula for the S-matrix can be derived by neglecting higher orders in mc-1 and relativistic correction related to charmonia. The S-matrix is related to the usual gluon distribution g(x) at small x. This result is different than those from other approaches. Confronting experiment the result is not in agreement with experimental measurement because large errors from higher order in mc-1 and from relativistic corrections. Nevertheless the ratio of cross sections of \jpsi and ψ(2S) can be predicted more precisely than cross-sections. In this letter we show that the ratio predicted in this approach with an estimation of relativistic corrections is in good agreement with the recent measurement at HERA.