Full Idea
The W and Z particles are heavy, and so cannot travel far from their parents. The weak force therefore has a very short range.
Gist of Idea
The weak force particles are heavy, so the force has a short range
Source
New Scientist writers (Why the Universe Exists [2017], 02)
Book Reference
New Scientist writers: 'Why the Universe Exists' [John Murray 2017], p.29