We analyze the photo-production of ηc,b off a proton in the threshold region, in terms of C-odd gluonic correlations in the off-forward proton matrix element. Near threshold, the skewness is large leading to a production amplitude that is dominated by four C-odd twist-3 gluon GPDs. We use the QCD instanton vacuum to estimate these C-odd contributions in the proton. The results are used to estimate the differential cross sections for coherent photo-production of ηc,b in the threshold region, at current electron facilities.
@article{arxiv.2404.03875,
title = {Photo-production of $\eta_{c,b}$ near Threshold},
author = {Wei-Yang Liu and Ismail Zahed},
journal= {arXiv preprint arXiv:2404.03875},
year = {2024}
}