Gluon-spin effects in hadronic jet production

After a brief overview on the baffling status of the proton spin content, we study the gluon-spin effects on the single-jet spin asymmetry ALLjet and on the polarized jet cross section ΔσLjet in proton-proton collisions. A measurement of ALLjet in the jet momentum region where the helicity asymmetry is dominated by gluon-quark hard scattering will furnish important information on the magnitude and even the sign of the gluon-spin component in a polarized proton. We find that ΔσLjet can be as large as ∼25 μb at √s =100 GeV, for example, if the European Muon Collaboration spin effect is explained in terms of large gluon polarization, while it is less than 1 μb if gluons are unpolarized