Calculation of transverse momentum dependent distributions beyond the leading power

Understand

We compute the contribution of twist-2 and twist-3 parton distribution functions to the small-$b$ expansion for transverse momentum dependent (TMD) distributions at all powers of $b$.

• The computation is done by the twist-decomposition method based on the spinor formalism for all eight quark TMD distributions.
• The newly computed terms are accompanied by the prefactor $(M^2b^2)^n$ and represent the target-mass corrections to the resummed cross-section.
• For the first time, a non-trivial expression for the pretzelosity distribution is derived.