Abstract
Polarisation asymmetries are measured for the hard exclusive leptoproduction of real photons from a longitudinally polarised hydrogen target. These asymmetries arise from the deeply virtual Compton scattering and Bethe-Heitler processes. From the data are extracted two asymmetries in the azimuthal distribution of produced real photons about the direction of the exchanged virtual photon: \( {\mathcal{A}_{\text{UL}}} \) with respect to the target polarisation and \( {\mathcal{A}_{\text{LL}}} \) with respect to the product of the beam and target polarisations. Results for both asymmetries are compared to the predictions from a generalised parton distribution model. The sin φ and cos(0φ) amplitudes observed respectively for the \( {\mathcal{A}_{\text{UL}}} \) and \( {\mathcal{A}_{\text{LL}}} \) asymmetries are compatible with the sizeable predictions from the model. Unexpectedly, a sin(2φ) modulation in the \( {\mathcal{A}_{\text{UL}}} \) asymmetry with a magnitude similar to that of the sin φ modulation is observed.
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ArXiv ePrint: 1004.0177
Now at: Brookhaven National Laboratory, Upton, New York 11772-5000, U.S.A.
Now at: Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, U.S.A.
Now at: Institut für Physik, Universität Mainz, 55128 Mainz, Germany
Now at: Institut für Kernphysik, Universität Frankfurt a.M., 60438 Frankfurt a.M., Germany
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HERMES collaboration., Airapetian, A., Akopov, N. et al. Exclusive leptoproduction of real photons on a longitudinally polarised hydrogen target. J. High Energ. Phys. 2010, 19 (2010). https://doi.org/10.1007/JHEP06(2010)019
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DOI: https://doi.org/10.1007/JHEP06(2010)019