Exclusive Leptoproduction of Real Photons on a Longitudinally Polarised Hydrogen Target

The HERMES Collaboration: A. Airapetian , N. Akopov , Z. Akopov , E.C. Aschenauer , W. Augustyniak , R. Avakian , A. Avetissian , E. Avetisyan

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B. Ball S. Belostotski N. Bianchi H.P. Blok H. Boettcher A. Borissov J. Bowles I. Brodski V. Bryzgalov J. Burns M. Capiluppi G.P. Capitani E. Cisbani G. Ciullo M. Contalbrigo P.F. Dalpiaz W. Deconinck R. De Leo L. De Nardo E. De Sanctis M. Diefenthaler P. Di Nezza M. Dueren M. Ehrenfried G. Elbakian F. Ellinghaus R. Fabbri A. Fantoni L. Felawka S. Frullani D. Gabbert G. Gapienko V. Gapienko F. Garibaldi G. Gavrilov V. Gharibyan F. Giordano S. Gliske M. Golembiovskaya C. Hadjidakis M. Hartig D. Hasch G. Hill A. Hillenbrand M. Hoek Y. Holler I. Hristova Y. Imazu A. Ivanilov A. Izotov H.E. Jackson H.S. Jo S. Joosten R. Kaiser G. Karyan T. Keri E. Kinney A. Kisselev N. Kobayashi V. Korotkov V. Kozlov P. Kravchenko V.G. Krivokhijne L. Lagamba R. Lamb L. Lapikas I. Lehmann P. Lenisa L.A. Linden-Levy A. Lopez~Ruiz W. Lorenzon X.-G. Lu X.-R. Lu B.-Q. Ma D. Mahon N.C.R. Makins S.I. Manaenkov L. Manfre Y. Mao B. Marianski A. Martinez de la Ossa H. Marukyan C.A. Miller Y. Miyachi A. Movsisyan V. Muccifora M. Murray A. Mussgiller E. Nappi Y. Naryshkin A. Nass M. Negodaev W.-D. Nowak L.L. Pappalardo R. Perez-Benito N. Pickert M. Raithel P.E. Reimer A.R. Reolon C. Riedl K. Rith G. Rosner A. Rostomyan J. Rubin D. Ryckbosch Y. Salomatin F. Sanftl A. Schaefer G. Schnell K.P. Schueler B. Seitz T.-A. Shibata V. Shutov M. Stancari M. Statera E. Steffens J.J.M. Steijger H. Stenzel J. Stewart F. Stinzing S. Taroian A. Terkulov A. Trzcinski M. Tytgat A. Vandenbroucke P.B. Van der Nat Y. Van Haarlem C. Van Hulse D. Veretennikov V. Vikhrov I. Vilardi C. Vogel S. Wang S. Yaschenko H. Ye Z. Ye S. Yen W. Yu D. Zeiler B. Zihlmann P. Zupranski

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classification ✦ hep-ex

keywords asymmetriestargetphotonsrealdistributionexclusivehydrogenleptoproduction

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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: A_UL with respect to the target polarisation and A_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(phi) and cos(0*phi) amplitudes observed respectively for the A_UL and A_LL asymmetries are compatible with the sizeable predictions from the model. Unexpectedly, a sin(2*phi) modulation in the A_UL asymmetry with a magnitude similar to that of the sin(phi) modulation is observed.

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Exclusive Leptoproduction of Real Photons on a Longitudinally Polarised Hydrogen Target

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