Document Type


Publication Date




Publication Title

Physical Review C






025203 (1-25)


We report on the measurement of the beam spin asymmetry in the deeply virtual Compton scattering off 4He using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab using a 6 GeV longitudinally polarized electron beam incident on a pressurized 4He gaseous target. We detail the method used to ensure the exclusivity of the measured reactions, in particular the upgrade of CLAS with a radial time projection chamber to detect the low-energy recoiling 4He nuclei and an inner calorimeter to extend the photon detection acceptance at forward angles. Our results confirm the theoretically predicted enhancement of the coherent (e4He→e′4Heγ′) beam spin asymmetries compared to those observed on the free proton, while the incoherent (e4He→ e′p′γ′X′) asymmetries exhibit a 30% suppression. From the coherent data, we were able to extract, in a model-independent way, the real and imaginary parts of the only 4He Compton form factor, HA, leading the way toward 3D imaging of the partonic structure of nuclei.


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Original Publication Citation

Dupré, R. Hattawy, M. Baltzell, N.A. ... Yale, B., Zachariou, N. & Zhang, J. (2021) Measurement of deeply virtual Compton scattering off 4He with the CEBAF large acceptance spectrometer at Jefferson Lab. Physical Review C, 104(2) 1-25, Article 025203.