title: Measurement of the spin asymmetry in the photoproduction of pairs of high- p(T) hadrons at HERMES
abstract: 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.
authors.affiliation: Yerevan Physics Institute, 375036, Yerevan, Armenia.
authors.initials: K
authors.lastname: McIlhany
authors.initials: RD
authors.lastname: McKeown
authors.initials: F
authors.lastname: Meissner
authors.initials: FM
authors.lastname: Menden
authors.initials: A
authors.lastname: Metz
authors.initials: N
authors.lastname: Meyners
authors.initials: O
authors.lastname: Mikloukho
authors.initials: CA
authors.lastname: Miller
authors.initials: MA
authors.lastname: Miller
authors.initials: R
authors.lastname: Milner
authors.initials: A
authors.lastname: Most
authors.initials: V
authors.lastname: Muccifora
authors.initials: Y
authors.lastname: Naryshkin
authors.initials: AM
authors.lastname: Nathan
authors.initials: F
authors.lastname: Neunreither
authors.initials: M
authors.lastname: Niczyporuk
authors.initials: W
authors.lastname: Nowak
authors.initials: TG
authors.lastname: O'Neill
authors.initials: R
authors.lastname: Openshaw
authors.initials: J
authors.lastname: Ouyang
authors.initials: BR
authors.lastname: Owen
authors.initials: SF
authors.lastname: Pate
authors.initials: S
authors.lastname: Potashov
authors.initials: DH
authors.lastname: Potterveld
authors.initials: G
authors.lastname: Rakness
authors.initials: R
authors.lastname: Redwine