Final State Interactions, T-odd PDFs & the Lensing Function

It has been suggested that under certain approximations the Sivers effect can be described in terms of factorization of final state interactions and a spatial distortion of impact parameter space parton distribution; that is a convolution of the so-called lensing function and the impact parameter GPD $E$. In this approach the lensing function is calculated in a non-perturbative eikonal model. This enables a comparison between the a priori distinct Sivers function and the GPD $E$ which goes beyond the discussion of overall signs.Comment: 5 pages, 5 figures, misprints corrected: To appear in the Proceedings of the 10th Conference on the Intersection of Particle and Nuclear Physics (CIPANP 2009) San Diego, CA, 25-31 May 200

Probing Gluonic Spin-Orbit Correlations in Photon Pair Production

We consider photon pair production in hadronic collisions at large mass and small transverse momentum of the pair, assuming that factorization in terms of transverse momentum dependent parton distributions applies. The unpolarized cross section is found to have azimuthal angular dependencies that are generated by a gluonic version of the Boer-Mulders function. In addition, the single-transversely polarized cross section is sensitive to the gluon Sivers function. We present simple numerical estimates for the Boer-Mulders and Sivers effects in diphoton production at RHIC and find that the process would offer unique opportunities for exploring transverse momentum dependent gluon distributions.Comment: 5 pages, 2 figures, minor changes, final version, to be published in PR

Final state interactions and the Sivers function

The non-vanishing of naive T-odd parton distributions function can be explained by the existence of the gauge link which emerges from the factorized description of the deep inelastic scattering cross section into perturbatively calculable and non-perturbative factors. This path ordered exponential describes initial / final-state interactions of the active parton due to soft gluon exchanges with the target remnants. Although these interactions are non-perturbative, studies of final state interactions have been approximated by perturbative one-gluon exchange in Abelian models. We include higher-order gluonic contributions from the gauge link by applying non-perturbative eikonal methods, incorporating color degrees of freedom in a calculation of the Sivers function. In this context we study the effects of color by considering the FSIs with Abelian and non-Abelian gluon interactions. We confirm the large $N_c$ QCD scaling behavior of Sivers functions and further uncover the deviations for finite $N_c$. Within this framework of FSIs we perform a quantitative check of approximate relations between T-odd TMDs and GPD which goes beyond the discussion of overall signs.Comment: 5 pages, 6 figures, To appear in the proceedings of the 12th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2010), May 31- June 4, 2010, Williamsburg VA, US