Measurement of the beam spin asymmetry of e→p→epη in the deep-inelastic regime with CLAS

The CLAS Collaboration

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The beam spin asymmetry of the exclusive pseudoscalar channel e→p→epη was measured for the first time in the deep-inelastic regime (W>2 GeV/c2 and Q2>1 GeV2/c2) 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 Q2, xB, −t and ϕ over a wide kinematic range, where ϕ is the azimuthal angle between the lepton and hadron scattering planes, The measured azimuthal dependence with large amplitudes of the sin⁡ϕ 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.

Original languageEnglish
Pages (from-to)426-431
Number of pages6
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Early online date3 Jan 2019
Publication statusPublished - 10 Feb 2019

Bibliographical note

© 2019 The Authors.


  • Chiral-odd generalized parton distributions
  • CLAS collaboration
  • Deeply Virtual Meson Production
  • Nucleon structure

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