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Measurement of the Beam-Spin Azimuthal Asymmetry Associated with Deeply-Virtual Compton Scattering

2001; American Physical Society; Volume: 87; Issue: 18 Linguagem: Inglês

10.1103/physrevlett.87.182001

1092-0145

A. Airapetian, Н. Акопов, Z. Akopov, M. Amarian, E. C. Aschenauer, H. Avakian, R. Avakian, A. Avetissian, E. Avetissian, P. Bailey, B. Bains, V. Baturin, C. Baumgarten, M. Beckmann, S. Belostotski, S. Bernreuther, N. Bianchi, H. Böttcher, A. Borissov, O. Bouhali, M. Bouwhuis, J. Brack, S. Brauksiepe, W. Brückner, A. Brüll, I. Brunn, H. J. Bulten, G. P. Capitani, P. Chumney, E. Cisbani, G. Ciullo, G.R. Court, P.F. Dalpiaz, R. De Leo, L. De Nardo, E. De Sanctis, D. De Schepper, E. Devitsin, P. K. A. de Witt Huberts, P. Di Nezza, M. Düren, M. Ehrenfried, G. Elbakian, F. Ellinghaus, J. Ely, R. Fabbri, A. Fantoni, A. Fechtchenko, L. Felawka, B. W. Filippone, H. Fischer, B. Fox, J. Franz, S. Frullani, Y. Gärber, F. Garibaldi, E. Garutti, G. Gavrilov, V. Gharibyan, A. Golendukhin, G. Graw, O. Grebeniouk, P. W. Green, L. G. Greeniaus, A. Gute, W. Haeberli, K. Hafidi, M. Hartig, D. Hasch, D. Heesbeen, F. H. Heinsius, M. Henoch, R. Hertenberger, W.H.A. Hesselink, G. Hofman, Y. Holler, R. J. Holt, B. Hommez, G. Iarygin, A. Izotov, H. E. Jackson, A. Jgoun, Peter Jung, R. Kaiser, J. Kanesaka, E. Kinney, A. Kisselev, P. Kitching, Hideaki Kobayashi, N. Koch, K. Königsmann, H. Kolster, В. А. Коротков, E. Kotik, В. Козлов, Bernhard Krauß, V. G. Krivokhijine, G. S. Kyle, L. Lagamba, A. Laziev, P. Lenisa, P. Liebing, T. Lindemann, W. Lorenzon, Axel Maas, N. C. R. Makins, H. Marukyan, F. Masoli, M. McAndrew, K. McIlhany, F. Meißner, F. Menden, N. Meyners, O. Mikloukho, C. A. Miller, R. Milner, V. Muccifora, R. Mussa, А. Нагайцев, E. Nappi, Y. Naryshkin, A. Nass, K. Negodaeva, W.‐D. Nowak, K. Oganessyan, T. G. O’Neill, B. Owen, S. F. Pate, S. Potashov, D. H. Potterveld, M. Raithel, G. Rakness, V. Rappoport, R. Redwine, D. Reggiani, A. R. Reolon, K. Rith, D. Robinson, A. Rostomyan, M. Ruh, D. Ryckbosch, Y. Sakemi, I. Sanjiev, Fuminobu Sato, I. Savin, C. Scarlett, A. Schäfer, C. Schill, Friedrich Schmidt, G. Schnell, K. P. Schüler, A. Schwind, J. Anthony Seibert, B. Seitz, T.-A. Shibata, V. Shutov, M. C. Simani, A. Simon, K. Sinram, E. Steffens, J. J. M. Steijger, J. Stewart, U. Stößlein, K. Suetsugu, S. Taroian, A. Terkulov, S. Tessarin, Eric Thomas, B. Tipton, M. Tytgat, G. M. Urciuoli, J. van den Brand, G. van der Steenhoven, J. van den Brand, J. van den Brand, M. C. Vetterli, V. Vikhrov, M. G. Vincter, J. Visser, C. Weiskopf, J. Wendland, Jürgen Wilbert, T. Wise, S. Yen, S. Yoneyama, H. Zohrabian,

High-Energy Particle Collisions Research

The beam-spin asymmetry in hard electroproduction of photons has been measured. The data have been accumulated by the HERMES experiment at DESY using the HERA 27.6 GeV longitudinally polarized positron beam and an unpolarized hydrogen-gas target. The asymmetry in the azimuthal distribution of the produced photons in the angle $\ensuremath{\varphi}$ relative to the lepton scattering plane was determined with respect to the helicity state of the incoming positron beam. The beam-spin analyzing power in the $\mathrm{sin}\ensuremath{\varphi}$ moment was measured to be $\ensuremath{-}0.23\ifmmode\pm\else\textpm\fi{}0.04(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.03(\mathrm{syst})$ in the missing-mass range below 1.7 GeV. The observed asymmetry is attributed to the interference of the Bethe-Heitler and deeply virtual Compton scattering processes.