7.2 The $W$ and $Z$ bosons mediate the weak interaction.
2.1 The first particle accelerator was built in 1930 by Cockcroft and Walton.
9.2 The gauge group of QCD is $SU(3)$.
6.1 The quark model predicts the existence of baryons and mesons.
2.3 The $\pi$ meson was discovered in 1947 by Cecil Powell.
6.2 The quark model explains the hadronic spectrum.
2.2 The concept of the neutrino was first proposed by Pauli in 1930.