Estimation of varUpsilon hbox {(1S)} production in ep process near threshold

Yu Xu,Rong Wang,Yaping Xie,Xurong Chen

doi:10.1140/epjc/s10052-020-7845-6

Abstract

The near-threshold photo-productions of heavy quarkonia are important ways to test the QCD-inspired models and to constrain the gluon distribution of nucleon in the large x region. Investigating the various models, we choose a photon–gluon fusion model and a pomeron exchange model for hbox {J}/varPsi photo-production near threshold, emphasising on the explanation of the recent experimental measurement by GlueX at JLab. We find that these two models are not only valid in a wide range of the center-of-mass energy of gamma and proton, but also can be generalized to describe the varUpsilon hbox {(1S)} photo-production. Using these two models, we predict the electro-production cross-sections of varUpsilon hbox {(1S)} at EicC to be 48 fb to 85 fb at the center-of-mass energy of 16.75 GeV.

Highlights

There are a lot of experiments that measured the J/Ψ photo-production, while the photo- and electro-production data of Υ (1S) at low energy are much scarce
The differential cross-section of the channel γ p → J/Ψ p is linked to the quantum chromodynamics (QCD) trace anomaly b [6,7], and proton mass decomposition
In principle the study on Υ (1S) photo-production near threshold better help us in extracting the trace anomaly b and in understanding the origins of the proton mass [8,9] compared to the J/Ψ channel

Summary

Introduction

There are a lot of experiments that measured the J/Ψ photo-production, while the photo- and electro-production data of Υ (1S) at low energy are much scarce. We notice that the PGF model and the pomeron exchange model are in good agreement with the old J/Ψ production data at both high and low energy. If they are consistent with the recent published data by GlueX and SLAC [16], they are suitable to reproduce the heavy quarkonia production from the threshold to a relatively high energy. As a consequence, these models are thought to be valid to fit the Υ (1S) production data at high energy and to extrapolate the cross-sections to a lower energy, even near the production threshold. The reason is that both J/Ψ and Υ (1S) have the heavy constituents moving slowly inside and are of the same quantum numbers

Photon–gluon fusion model

Pomeron exchange model

Discussions and summary