Initial-State Interactions in the Unpolarized Drell-Yan Process
- SLAC
We show that initial-state interactions contribute to the cos 2{phi} distribution in unpolarized Drell-Yan lepton pair production p p and p {bar p} {yields} {ell}{sup +}{ell}{sup -} X, without suppression. The asymmetry is expressed as a product of chiral-odd distributions h{sub 1}{sup {perpendicular}} (x{sub 1}, p{sub {perpendicular}}{sup 2}) x {bar h}{sub 1}{sup {perpendicular}} (x{sub 2}, k{sub {perpendicular}}{sup 2}), where the quark-transversity function h{sub 1}{sup {perpendicular}}(x, p{sub {perpendicular}}{sup 2}) is the transverse momentum dependent, light-cone momentum distribution of transversely polarized quarks in an unpolarized proton. We compute this (naive) T-odd and chiral-odd distribution function and the resulting cos 2{psi}asymmetry explicitly in a quark-scalar diquark model for the proton with initial-state gluon interaction. In this model the function h{sub 1}{sup {perpendicular}} (x{sub 1}, p{sub {perpendicular}}{sup 2}) equals the T-odd (chiral-even) Sivers effect function f{sub 1T}{sup {perpendicular}}(x, p{sub {perpendicular}}{sup 2}). This suggests that the single-spin asymmetries in the SIDIS and the Drell-Yan process are closely related to the cos 2{phi} asymmetry of the unpolarized Drell-Yan process, since all can arise from the same underlying mechanism. This provides new insight regarding the role of quark and gluon orbital angular momentum as well as that of initial- and final-state gluon exchange interactions in hard QCD processes.
- Research Organization:
- Stanford Linear Accelerator Center, Menlo Park, CA (US)
- Sponsoring Organization:
- USDOE Office of Science (US)
- DOE Contract Number:
- AC03-76SF00515
- OSTI ID:
- 808666
- Report Number(s):
- SLAC-PUB-9561
- Country of Publication:
- United States
- Language:
- English
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