Modeling Backward-Angle ($u$-channel) Virtual Compton Scattering at an Electron-Ion Collider

TL;DR

This paper explores the potential to study backward Compton scattering at the future Electron-Ion Collider, modeling cross-sections and detector responses to understand the process and background rejection capabilities.

Contribution

It provides the first modeling and simulation of backward Compton scattering at EIC energies, assessing experimental feasibility and background suppression methods.

Findings

Backward Compton scattering can be effectively studied at EIC.

High-resolution ZDC can reject background from backward π^0 production.

Proton and photon kinematics are suitable for detection at EIC.

Abstract

High-energy backward ($u$-channel) reactions can involve very large momentum transfers to the target baryons, shifting them by many units of rapidity. These reactions are difficult to understand in conventional models in which baryon number is carried by the valence quarks. Backward Compton scattering is an especially attractive experimental target, because of its simple final state. There is currently limited data on this process, and that data is at low center-of-mass energies. In this paper, we examine the prospects for studying backward Compton scattering at the future Electron-Ion Collider (EIC). We model the cross-section and kinematics using the limited data on backward Compton scattering and backward meson production, and then simulate Compton scattering at EIC energies, in a simple model of the ePIC detector. Generally, the proton is scattered toward mid-rapidity, while the produced photon is in the far-forward region, visible in a Zero Degree Calorimeter (ZDC). We show that the background from backward $\pi^0$ production can be rejected using a high-resolution, well-segmented ZDC.