Transverse momentum distributions

In high energy particle physics, specifically in hadron-beam scattering experiments, transverse momentum distributions (TMDs) are the distributions of the hadron's quark or gluon momenta that are perpendicular to the momentum transfer between the beam and the hadron. Specifically, they are probability distributions to find inside the hadron a parton with a transverse momentum k T {\displaystyle k_{T}} and longitudinal momentum fraction x {\displaystyle x} .

Source: Wikipedia — Transverse momentum distributions (CC BY-SA 4.0)