Left-click: rotate, Mouse-wheel/middle-click: zoom, Right-click: pan, Escape: close
Interactions
Exchange particles (bosons)
- Repulsion - explained by exchange of photon. This is why electrons move away from each other!!
- Note that in this case, the photons are virtual, i.e. we can't detect them.
- They still exchange photons when its a positive and negative particle interacting, so :)
- Feynmann diagram
- Exchange particle (Boson)
If there was a positron, it moves backwards in time because they're antimatter. Awesome?
- QED - Quantum Electrodynamics, which explains the mechanism of electromagnetic force.
In contrast, the strong force is mediated by gluons.
Interactions governed by properties associated with colour...?! (another quantum property like charge but not like charge)
Weak interaction has 2 bosons ($W^{+},W^{-}, Z^0$)
When particles interact, things are conserved:
- Charge
- Baryon number
- Quarks have $+ \frac{1}{3}$
- Electrons have $0$
- Protons have $+1$ (Baryons have $+1$...)
- Antiproton $-1$
- Lepton number
- Electron has $+1$ (same with $\mu$ and $\tau$)
- Generation ($e, \mu, \tau$)
- If you get x amounts of electrons/electron neutrinos, you need to get x amounts of electrons/electron neutrinos back. Note that antiparticles have negative of these values (excluding mass)
- e.g. $n\to p+e^{-}+\bar{v_{e}}$
$\beta$ decay
$$\begin{align}
C\to \beta + N + \bar{v_{e}}
\end{align}
$$
What's actually happening is that a neutron is decay to a proton, an electron and an antielectron neutrino.
This is to conserve the lepton number (/generation).
i.e.
$$\begin{align}
udd\to uud + e^{-} + \bar{v_{e}}
\end{align}
$$
If you do the math (and remember that the antiparticle has the opposite quantum property), you find out that the charge, lepton number and baryon number are the same on both sides! This makes it a valid particle interaction.
Pions (mesons)
Pions are a specific subset of mesons, i.e. quark-anti-quark pairs. They only consist of the possible combinations of up and down quarks.
- $\pi ^+$ - $u \bar{d}$
- $\pi ^0$ - $u \bar{u}$, $d \bar{d}$
- $\pi ^-$ - $d \bar{u}$
Pions can decay into big things (muons)
$\pi ^{+}\to \mu^+ + v_{\mu}$
|
Charge |
Baryon number |
Muon number |
| Reactants |
+1=+1 |
+1/3 + -1/3 = 0 |
0=0 |
| Products |
+1+0=+1 |
0+0=0 |
+-1+1=0 |
| Net |
+1-+1=0 $\checkmark$ |
0-0=0 $\checkmark$ |
0-0=0 $\checkmark$ |
- Recall that all mesons necessarily have baryon number of $0$.
Particles to interactions
Which particle governs which?
- $W^{+},W^{-}, Z^0$ - weak electrons
- $W^{+},W^{-}$ - beta decay and other transmutations involving charge
- $Z^{0}$ - neutrino scattering, etc. uncommon things
