Introduction To Elementary Particles Solutions Manual Griffiths -

9.1 The gauge group of QED is $U(1)$.

6.1 The quark model predicts the existence of baryons and mesons.

1.3 The antiparticle of the electron $e^{-}$ is the positron $e^{+}$.

2.3 The $\pi$ meson was discovered in 1947 by Cecil Powell.