The QCD Evolution of the Sivers Function

Understand

We extend the Collins-Soper-Sterman (CSS) formalism to apply it to the spin-dependence governed by the Sivers function.

• We use it to give a correct numerical QCD evolution of existing fixed-scale fits of the Sivers function.
• With the aid of approximations useful for the non-perturbative region, we present the results as parametrizations of a Gaussian form in transverse momentum space, rather than in the Fourier conjugate transverse coordinate space normally used in the CSS formalism.
• They are specifically valid at small transverse momentum.