Final-State Interactions and Single-Spin Asymmetries in Semi-Inclusive Deep Inelastic Scattering
- SLAC
Recent measurements from the HERMES and SMC collaborations show a remarkably large azimuthal single-spin asymmetries AUL and AUT of the proton in semi-inclusive pion leptoproduction {gamma}*(q)p {yields} {pi}X. We show that final-state interactions from gluon exchange between the outgoing quark and the target spectator system lead to single-spin asymmetries in deep inelastic lepton-proton scattering at leading twist in perturbative QCD; i.e., the rescattering corrections are not power-law suppressed at large photon virtuality Q{sup 2} at fixed x{sub bj}. The existence of such single-spin asymmetries requires a phase difference between two amplitudes coupling the proton target with J{sub P}{sup z} = {+-} 1/2 to the same final-state, the same amplitudes which are necessary to produce a nonzero proton anomalous magnetic moment. We show that the exchange of gauge particles between the outgoing quark and the proton spectators produces a Coulomb-like complex phase which depends on the angular momentum L{sup z} of the proton's constituents and is thus distinct for different proton spin amplitudes. The single-spin asymmetry which arises from such final-state interactions does not factorize into a product of distribution function and fragmentation function, and it is not related to the transversity distribution {delta}q(x, Q) which correlates transversely polarized quarks with the spin of the transversely polarized target nucleon.
- Research Organization:
- Stanford Linear Accelerator Center, Menlo Park, CA (US)
- Sponsoring Organization:
- USDOE Office of Energy Research (ER) (US)
- DOE Contract Number:
- AC03-76SF00515
- OSTI ID:
- 799001
- Report Number(s):
- SLAC-PUB-9135
- Country of Publication:
- United States
- Language:
- English
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