Next-to-leading order forward hadron production in the small-$x$ regime: rapidity factorization

Understand

Single inclusive hadron production at forward rapidity in high energy p+A collisions is an important probe of the high gluon density regime of QCD and the associated small-$x$ formalism.

• We revisit an earlier one-loop calculation to illustrate the significance of the "rapidity factorization" approach in this regime.
• Such factorization separates the very small-$x$ unintegrated gluon density evolution and leads to a new correction term to the physical cross section at one-loop level.
• Importantly, this rapidity factorization formalism remedies the previous unphysical negative next-to-leading order contribution to the cross section.