Diffractive photoproduction of ηc Original Research Article

Diffractive photoproduction of ηc is an important process to study the effect of Odderon, whose existence is still not confirmed in experiment. A detailed interpretation of Odderon in QCD, i.e., in terms of gluons is also unclear. Taking charm quarks as heavy quarks, we can use NRQCD and take ηc as a View the MathML source bound state. Hence, in the production of ηc a free View the MathML source pair is first produced and this pair is transformed into ηc subsequently. In the forward region of the kinematics, the View the MathML source pair interacts with initial hadron through exchanges of soft gluons. This interaction can be studied with HQET, which provides a systematic expansion in the inverse of the c quark mass mc. We find that the calculation of the S-matrix element in the forward region can be formulated as the problem of solving a wave function of a c quark propagating in a background field of soft gluons. At leading order we find that the differential cross-section can be expressed with four functions, which are defined with a twist-3 operator of gluons. The effect of exchanging a Odderon can be identified with this operator in our case. We discuss our results in detail and compare them with those obtained in previous studies. Our results and those from other studies show that the differential cross-section is very small in the forward region. We also show that the production through photon exchange is dominant in the extremely forward region, hence the effect of Odderon exchange cannot be identified in this region. For completeness we also give results for diffractive photoproduction of J/Ψ.