Single-spin observables and orbital structures in hadronic distributions
- Portland Physics Institute, 4730 SW Macadam, Suite 101, Portland, Oregon 97239 (United States) and Spin Physics Center, University of Michigan, Ann Arbor, Michigan 48109-1120 (United States)
Single-spin observables in scattering processes (either analyzing powers or polarizations) are highly constrained by rotational invariance and finite symmetries. For example, it is possible to demonstrate that all single-spin observables are odd under the finite transformation O=PA{sub {tau}} where P is parity and A{sub {tau}} is a finite symmetry that can be designated 'artificial time reversal'. The operators P, O and A{sub {tau}} all have eigenvalues {+-}1 so that all single-spin observables can be classified into two distinct categories: (1) P-odd and A{sub {tau}}-even (2) P-even and A{sub {tau}}-odd. Within the light-quark sector of the standard model, P-odd observables are generated from pointlike electroweak processes while A{sub {tau}}-odd observables (neglecting quark mass parameters) come from dynamic spin-orbit correlations within hadrons or within larger composite systems, such as nuclei. The effects of A{sub {tau}}-odd dynamics can be inserted into transverse-momentum dependent constituent distribution functions and, in this paper, we construct the contribution from an orbital quark to the A{sub {tau}}-odd quark parton distribution {delta}{sup N}G{sub q/p{up_arrow}}{sup front}(x,k{sub TN};{mu}{sup 2}). Using this distribution, we examine the crucial role of initial- and final-state interactions in the observation of the scattering asymmetries in different hard-scattering processes. This construction provides a geometrical and dynamical interpretation of the Collins conjugation relation between single-spin asymmetries in semi-inclusive deep inelastic scattering and the asymmetries in Drell-Yan production. Finally, our construction allows us to display a significant difference between the calculation of a spin asymmetry generated by a hard-scattering mechanism involving color-singlet exchange (such as a photon) and a calculation of an asymmetry with a hard-scattering exchange involving gluons. This leads to an appreciation of the process-dependence inherent in measurements of single-spin observables.
- OSTI ID:
- 20873133
- Journal Information:
- Physical Review. D, Particles Fields, Vol. 74, Issue 9; Other Information: DOI: 10.1103/PhysRevD.74.094008; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
- Country of Publication:
- United States
- Language:
- English
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ASYMMETRY
COLOR MODEL
CORRELATIONS
D QUARKS
DEEP INELASTIC SCATTERING
DISTRIBUTION
DISTRIBUTION FUNCTIONS
DRELL MODEL
EIGENVALUES
FIELD OPERATORS
FINAL-STATE INTERACTIONS
GLUONS
HADRONS
PARITY
PHOTONS
POLARIZATION
POLARIZATION-ASYMMETRY RATIO
REST MASS
ROTATIONAL INVARIANCE
SPIN
STANDARD MODEL
SYMMETRY
TRANSVERSE MOMENTUM
U QUARKS