Measurement of the beam spin asymmetry of (e)over-right-arrowp → e′p′η′ in the deep-inelastic regime with CLAS

The beam spin asymmetry of the exclusive pseudoscalar channel (e) over right arrowp -> e'p'eta was measured for the first time in the deep-inelastic regime (W > 2 GeV/c(2) and Q(2) > 1 GeV2/c(2)) using a longitudinally polarized 5.78 GeV electron beam at Jefferson Lab with the CEBAF Large Acceptance Spectrometer. The data were accumulated in 144 four-dimensional bins of Q(2), chi(B), -t and phi over a wide kinematic range, where phi is the azimuthal angle between the lepton and hadron scattering planes, The measured azimuthal dependence with large amplitudes of the sin phi moments is a clear indication of a substantial contribution to the polarized cross-section from transversely polarized virtual photons. In the framework of generalized parton distributions (GPDs) this contribution is expressed via longitudinal-transverse interference between chiral-even and chiral-odd GPDs. The experimental results are compared to the existing theoretical models demonstrating the sensitivity to the product of chiral-odd and chiral-even GPDs and provide new constraints to the existing GPD parameterizations. (C) 2019 The Authors. Published by Elsevier B.V.