Measurement of the Spin Asymmetry in the Photoproduction of Pairs of High- pT Hadrons at HERMES

Creators: Airapetian, A.; Akopov, N.; Amarian, M.; Aschenauer, E. C.; Avakian, H.; Avakian, R.; Avetissian, A.; Bains, B.; Baumgarten, C.; Beckmann, M.; Belostotski, S.; Belz, J. E.; Benisch, Th.; Bernreuther, S.; Bianchi, N.; Blouw, J.; Böttcher, H.; Borissov, A.; Brack, J.; Brauksiepe, S.; Braun, B.; Brückner, W.; Brüll, A.; Bulten, H. J.; Capitani, G. P.; Carter, P.; Chumney, P.; Cisbani, E.; Court, G. R.; Dalpiaz, P. F.; De-Sanctis, E.; De-Schepper, D.; Devitsin, E.; de-Witt-Huberts, P. K. A.; Di-Nezza, P.; Düren, M.; Dvoredsky, A.; Elbakian, G.; Ely, J.; Fantoni, A.; Ferstl, M.; Fiedler, K.; Filippone, B. W.; Fischer, H.; Fox, B.; Franz, J.; Frullani, S.; Funk, M.-A.; Gärber, Y.; Garibaldi, F.; Gavrilov, G.; Geiger, P.; Gharibyan, V.; Golendukhin, A.; Graw, G.; Grebeniouk, O.; Green, P. W.; Greeniaus, L. G.; Grosshauser, C.; Guidal, M.; Gute, A.; Haeberli, W.; Hansen, J.-O.; Hasch, D.; Häusser, O.; Heinsius, F. H.; Henderson, R.; Henoch, M.; Hertenberger, R.; Holler, Y.; Holt, R. J.; Hoprich, W.; Ihssen, H.; Iodice, M.; Izotov, A.; Jackson, H. E.; Jgoun, A.; Kaiser, R.; Kinney, E.; Kisselev, A.; Kitching, P.; Kobayashi, H.; Koch, N.; Königsmann, K.; Kolstein, M.; Kolster, H.; Korotkov, V.; Korsch, W.; Kozlov, V.; Kramer, L. H.; Kurisuno, M.; Kyle, G.; Lachnit, W.; Lorenzon, W.; Makins, N. C. R.; Martens, F. K.; Martin, J. W.; Masoli, F.; Mateos, A.; McAndrew, M.; McIlhany, K.; McKeown, R. D.; Meissner, F.; Menden, F. M.; Metz, A.; Meyners, N.; Mikloukho, O.; Miller, C. A.; Miller, M. A.; Milner, R.; Most, A.; Muccifora, V.; Naryshkin, Y.; Nathan, A. M.; Neunreither, F.; Niczyporuk, M.; Nowak, W.-D.; O'Neill, T. G.; Openshaw, R.; Ouyang, J.; Owen, B. R.; Pate, S. F.; Potashov, S.; Potterveld, D. H.; Rakness, G.; Redwine, R.; Reolon, A. R.; Ristinen, R.; Rith, K.; Rossi, P.; Rudnitsky, S.; Ruh, M.; Ryckbosch, D.; Sakemi, Y.; Scarlett, C.; Schäfer, A.; Schmidt, F.; Schmitt, H.; Schnell, G.; Schüler, K. P.; Schwind, A.; Seibert, J.; Shibata, T.-A.; Shibatani, K.; Shin, T.; Shutov, V.; Simani, C.; Simon, A.; Sinram, K.; Slavich, P.; Spengos, M.; Steffens, E.; Stenger, J.; Stewart, J.; Stoesslein, U.; Sutter, M.; Tallini, H.; Taroian, S.; Terkulov, A.; Tipton, B.; Tytgat, M.; Uriuoli, G. M.; van-de-Vyver, R.; van-den-Brand, J. F. J.; van-der-Steenhoven, G.; van-Hunen, J. J.; Vetterli, M. C.; Vikhrov, V.; Vincter, M. G.; Visser, J.; Volk, E.; Wander, W.; Wendland, J.; Williamson, S. E.; Wise, T.; Woller, K.; Yoneyama, S.; Zohrabian, H.

Abstract

We present a measurement of the longitudinal spin asymmetry A|| in photoproduction of pairs of hadrons with high transverse momentum pT. Data were accumulated by the HERMES experiment using a 27.5 GeV polarized positron beam and a polarized hydrogen target internal to the HERA storage ring. For h^+h^- pairs with _(pT)^(h1)>1.5GeV/c and _(pT)^(h2)>1.0GeV/c, the measured asymmetry is A_(||) = -0.28±0.12(stat)±0.02(syst). This negative value is in contrast to the positive asymmetries typically measured in deep inelastic scattering from protons, and is interpreted to arise from a positive gluon polarization.

Additional Information

© 2000 The American Physical Society. Received 15 July 1999. We gratefully acknowledge the DESY management for its support, the DESY staff and the staffs of the collaborating institutions for their significant effort, and our funding agencies for financial support.

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