In the standard model, every Feynman diagram is constructed using a combination of specific vertices. Here, q represents any quark, g stands for a gluon, X denotes any charged particle, γ symbolizes a photon, f signifies any fermion, m refers to any particle that has mass (except potentially neutrinos), and so on.
When a diagram features multiple particle labels divided by a "/", one of these labels is selected. Conversely, if the particle labels are separated by a "|", they must be chosen in sequential order.