Application Of Conservation Laws
This lesson covers:
- Creation and decay of strange particles
- Conservation laws obeyed in particle interactions
- How conservation laws apply differently for strong and weak interactions
Strange particles
Strange particles have a quantum property called strangeness that is conserved in strong interactions.
Strangeness number:
- Quarks have strangeness of -1, 0 or +1
Strange quarks are produced in the strong interaction and decay by the weak interaction.
To conserve strangeness, strange particles must be created or destroyed in pairs by strong interactions.
Worked example - Production of Kaons
Kaons are produced via the strong interaction:
P+P→P+P+K++K−
The table below shows how strangeness, baryon number, lepton number and charge are conserved during the production of Kaons.
| Property | Calculation |
|---|---|
| Strangeness (s) | 0 + 0 0 + 0 + 1 + (-)1 |
| Baryon number (B) | 1 + 1 1 + 1 + 0 + 0 |
| Lepton number (L) | 0 + 0 0 + 0 + 0 + 0 |
| Charge (Q) | 1 + 1 1 + 1 +1 + (-)1 |
Conservation laws in particle interactions
In order for an interaction to be possible, some properties must be conserved.
The following must always be conserved:
- Energy
- Momentum
- Charge
- Baryon number
- Lepton numbers
Strangeness is also conserved in strong interactions.
Decay of a strange particle
Strange particles decay via the weak interaction.
The strangeness can change by +1, 0, or -1 in weak interactions.
An example of weak decay is:
K+→μ+ + νμ
In this interaction the strangeness has changed from -1 to 0.
| K+ | |
|---|---|
| Baryon Number (B) | 0 + 0 |
| Lepton Number (L) | -1 + 1 |
| Strangeness (S) | -1 0 + 0 |
| Charge (Q) | 1 + 0 |