Nuclear Physics & RIKEN Theory Seminar

In hadron collisions, the single transverse spin asymmetry (STSA) is an observable describing the left-right asymmetry in the spectrum of produced particles when one of the colliding hadrons is polarized transverse to the beam axis. Since the discovery of unexpectedly large STSA's at the Tevatron in the 1990's, these spin asymmetries have consistently challenged accepted paradigms in factorization, universality, and perturbative QCD. Current theoretical treatments describe the generation of asymmetry in two nonperturbative sectors: the intrinsic parton distribution functions (Sivers effect) and the fragmentation functions (Collins effect). In this talk, I will discuss how the systematic enhancement of certain scattering processes for high energies or large nuclei (saturation formalism) leads to an asymmetry that can be generated at the perturbative level. Our new mechanism generates the STSA through a C-odd scattering process known as the “odderon,” a hypothetical interaction originating from the field of Regge physics. I will present our general result deriving the new mechanism and some numerical estimates illustrating its features. I will conclude by describing some of the scaling properties of our mechanism and illustrating its essential features.