PX156 - F6 - conservation of quantum numbers in interactions

for an interaction to happen, quantum numbers need to be conserved through the interaction
steve's list:
- Q
- B
- L
- $L_{e}, L_{τ}, L_{μ}$
- flavour (if violates: weak interaction)
- for decays: 1 particle $\to n$ particles
  - total mass has to be conserved in the rest frame of the initial particle
eg: can this interaction happen?

p \to π^{0} (u \bar{u}) + e^{+} + {\bar{ν}}_{e}

- $Q : + 1 \to + 0 + 1 + 0 :$ conserved
- $B : + 1 \to + 0 + 0 + 0 :$ not conserved
- therefore, it cannot happen

ρ^{0} (u \bar{u}) \to π^{+} (u \bar{d}) + π^{-} (\bar{u} d)

- $Q : 0 \to 1 - 1 :$ conserved
- $B : 0 \to 0 + 0 :$ conserved
- $L : 0 \to 0 + 0 :$ conserved
- flavour:
- $u : + \frac{1}{2} - \frac{1}{2} \to [+ \frac{1}{2} + 0] + [- \frac{1}{2} + 0] :$ conserved
- $d :$ conserved as well
- $c, s, t, b : 0$
- mass:
- $M (ρ) = 770 M e v / c^{2}$
- $M (π) = 139 M e v / c^{2}$
- $M (ρ) > 2 \times M (π)$
- interaction can happen