Beam spin asymmetry in the electroproduction of a pseudoscalar meson or a scalar meson off the scalar target

We discuss the electroproduction of a pseudoscalar ($0^{-+}$) meson or a scalar ($0^{++}$) meson off the scalar target. The most general formulation of the differential cross section for the $0^{-+}$ or $0^{++}$ meson process involves only one or two hadronic form factors, respectively, on a scalar target. The Rosenbluth-type separation of the differential cross section provides the explicit relation between the hadronic form factors and the different parts of the differential cross section in a completely model-independent manner. The absence of the beam spin asymmetry for the pseudoscalar meson production provides a benchmark for the experimental data analysis. The measurement of the beam spin asymmetry for the scalar meson production may also provide a unique opportunity not only to explore the imaginary part of the hadronic amplitude in the general formulation but also to examine the significance of the chiral-odd generalized parton distribution (GPD) contribution in the leading-twist GPD formulation.

Figure 1

Momentum assignments in the meson electroproduction process with one-photon-exchange.

Figure 2

Target rest frame kinematics for the meson electroproduction.