Backward-Angle ($u$-channel) Production at an Electron-Ion Collider

Abstract

In backward photoproduction of mesons, $γp\rightarrow M p$, the target proton takes most of the photon momentum, while the produced meson recoils in the direction from which the photon came. Thus the Mandelstam $u$ is small, while the squared momentum transfer $t$ is typically large, near the kinematic limit. In a collider geometry, backward production transfers the struck baryon by many units of rapidity, in a striking similarity to baryon stopping. We explore this similarity, and point out the similarities between the Regge theories used to model baryon stopping with those that are used for backward production. We then explore how backward production can be explored at higher energies than are available at fixed target experiments, by studying production at an electron-ion collider. We calculate the expected $ep$ cross sections and rates, finding that the rate for backward $ω$ production is about 1/300 that of forward $ω$s. We discuss the kinematics of backward production and consider the detector requirements for experimental study.