Spin-dependent parton distributions in polarized deep inelastic lepton nucleon scattering

Abstract

We analyze the recently measured first moment Г^p(Q ²) of the structure functiong ^p₁ (x,Q ²) obtained in deep inelastic scattering of polarized electrons from polarized protons. It is shown that the recent experimental result Г^p(〈Q ²〉≃10 GeV²)≃ 0.113 implies a polarized strange quark sea whose total polarization Δs(μ²)≃−0.22 is comparable to Δμ(μ²)≃0.74 and Δd(μ²)≃−0.50 already at a typically hadronic scale μ=0(1 GeV). Most remarkably, the total polarization due to quark distributions Δμ(μ²)+Δd(μ²)+Δs(μ²) practically vanishes which implies that the spin of the proton is carried by the gluons, ΔG(μ²), and/or the angular momentum of the partons. This surprising conjecture can be experimentally tested with heavy quark production in longitudinally polarized lepton-nucleon scattering. In particular the (real) photon-gluon fusion process γg→Q $\bar Q$ provides a rather unique measure of ΔG(x,Q ²).