/ Experiment-HEP hep-ex/0612059

Beam-Spin Asymmetries in the Azimuthal Distribution of Pion Electroproduction

Airapetian, A. ; Akopov, Z. ; Amarian, M. ; Andrus, A. ; Aschenauer, E.C. ; Augustyniak, W. ; Avakian, H. ; Avakian, R. ; Avetissian, A. ; Avetisyan, E. ; Bacchetta, A. ; Bailey, P. ; Belostotski, S. ; Bianchi, N. ; Blok, H.P. ; Bottcher, H. ; Borissov, A. ; Borysenko, A. ; Brull, A. ; Bryzgalov, V. ; Capiluppi, M. ; Capitani, G.P. ; Ciullo, G. ; Contalbrigo, M. ; Dalpiaz, P.F.

Published in: Phys.Lett.
Year: 2007
Vol.: B648
Page No: 164-170

Abstract: A measurement of the beam-spin asymmetry in the azimuthal distribution of pions produced in semi-inclusive deep-inelastic scattering off protons is presented. The measurement was performed using the {HERMES} spectrometer with a hydrogen gas target and the longitudinally polarized 27.6 GeV positron beam of HERA. The sinusoidal amplitude of the dependence of the asymmetry on the angle $\phi$ of the hadron production plane around the virtual photon direction relative to the lepton scattering plane was measured for $\pi^+,\pi^-$ and $\pi^0$ mesons. The dependence of this amplitude on the Bjorken scaling variable and on the pion fractional energy and transverse momentum is presented. The results are compared to theoretical model calculations.

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