On the kinematic constraint in BFKL near threshold region

TL;DR

This paper introduces a modified BFKL equation incorporating a kinematic constraint to better describe small x evolution near the threshold, showing significant effects on particle yields in high-energy collisions.

Contribution

It presents a novel BFKL equation with a rapidity veto from kinematic constraints, emphasizing its importance near the threshold region.

Findings

Particle yield at large transverse momentum is suppressed near the threshold.

The kinematic constraint significantly impacts small x evolution.

Phenomenological implications for pp and eA collisions are demonstrated.

Abstract

We introduce a modified Balitskii-Fadin-Kuraev-Lipatov (BFKL) equation with the rapidity veto that originates from external kinematic constraint. Though it is a formally sub-leading power contribution, such kinematic effect becomes very important especially in the threshold region, where there is no sufficient phase space for the small $x$ evolution to be fully developed. We also investigate the phenomenological consequences of the kinematic constraint BFKL equation in the forward particle production processes in pp and eA collisions. It is shown that particle yield at large transverse momentum is significantly suppressed in the threshold region.