Abstract

We report a new measurement of the midrapidity inclusive jet longitudinal double-spin asymmetry, A(LL), in polarized pp collisions at center-of-mass energy root s = 200 GeV. The STAR data place stringent constraints on polarized parton distribution functions extracted at next-to-leading order from global analyses of inclusive deep-inelastic scattering (DIS), semi-inclusive DIS, and RHIC pp data. The measured asymmetries provide evidence at the 3 sigma level for positive gluon polarization in the Bjorken-x region x > 0.05.