Introduction
natural units:
- MeV
- fm (1 fm = $10^{-15}$ m)
- barn (1 b = 10$^{-28}$ m$^2$)
- $\hbar = c = 1$
- mass, energy and momentum have the same units
- $\hbar c = 197.3$ MeV fm
- $(\hbar c)^2 = 0.3894$ GeV$^2$ mb
fine structure constant $\alpha=\frac{e^2}{4\pi \hbar c}$. Defining a 'strong nuclear charge' $\alpha_s \sim 1$ at a distance of a few fermi.
The scale of weak interactions is given by the Fermi constant $G_F/(\hbar c)^3 = 1.166 \times 10^{-5} GeV^{-2}$.
- the muon by Anderson and Neddermeyer in 1936 using a cloud chamber within a magnetic field;
- the pion in 1947 by Powell’s group in Bristol using specially developed photographic emulsion;
- 'strange particles' by Rochester and Butler (1946–47) using a coincidence-counter-controlled cloud chamber. a much longer lifetime than would be expected for a ‘normal’ strongly interacting particle with a comparable mass.
- A new quantum number, strangeness, Gell-Mann and Nishijima in 1953
- early 1950, synchrotrons with GeV energy