# Soft gluons and colinear gluons

by varphi42
Tags: colinear, gluons, soft
 P: 323 Usually soft gluons are those with low momentum, i.e. the less energetic ones, while collinear gluons are those produced near the beam direction, i.e. with low PT. Obviously a gluon can be both soft and collinear. In fact, one can show that gluons are mostly emitted soft AND collinear as the probability of emitting a gluon from a quark is given by: $$dP_{q\rightarrow qg}\propto \frac{dk}{k}\frac{dk_\perp^2}{k_\perp^2}$$ and so the probability is strongly centered around k≈0 (soft) and PT≈0 (collinear).