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 pairs with ph1 T>1.5GeV/c and ph2 T>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.
ASJC Scopus subject areas
- Physics and Astronomy(all)