Threshold factorization of the Drell-Yan process at next-to-leading power

Understand

We present a factorization theorem valid near the kinematic threshold $z=Q^2/\hat{s}\to 1$ of the partonic Drell-Yan process $q\bar q\to\gamma^*+X$ for general subleading powers in the $(1-z)$ expansion.

• We then consider the specific case of next-to-leading power.
• We discuss the emergence of collinear functions, which are a key ingredient to factorization starting at next-to-leading power.
• We calculate the relevant collinear functions at $\mathcal{O}(\alpha_s)$ by employing an operator matching equation and we compare our results to the expansion-by-regions computation up to the next-to-next-to-leading order, finding agreement.