Measurement of the spin asymmetry in the photoproduction of pairs of high- p(T) hadrons at HERMES

• Published in: Physical review letters Vol. 84; no. 12; p. 2584
• Main Authors: McIlhany, K, McKeown, RD, Meissner, F, Menden, FM, Metz, A, Meyners, N, Mikloukho, O, Miller, CA, Miller, MA, Milner, R, Most, A, Muccifora, V, V, Naryshkin, Y, Nathan, AM, Neunreither, F, Niczyporuk, M, Nowak, W, O'Neill, TG, Openshaw, R, Ouyang, J, Owen, BR, Pate, SF, Potashov, S, Potterveld, DH, Rakness, G, Redwine, R
• Format: Journal Article
• Language: English
• Published: United States 20.03.2000
• ISSN: 1079-7114
• DOI: 10.1103/PhysRevLett.84.2584

We present a measurement of the longitudinal spin asymmetry A(||) in photoproduction of pairs of hadrons with high transverse momentum p(T). 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 p(h(1))(T)>1.5 GeV/c and p(h(2))(T)>1.0 GeV/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.