BRAINCAKEConservation Rules
Every particle interaction must obey a set of conservation rules. Checking these is how you decide whether a proposed interaction or decay can happen.
Energy (including rest energy), momentum and charge are conserved in all interactions. The total charge before must equal the total charge after.
Baryon number is always conserved. Baryons have B = +1, antibaryons B = -1, and mesons and leptons B = 0. Lepton number is also always conserved, and electron lepton number and muon lepton number must be conserved separately.
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Key terms in this lesson
- Strong nuclear force
- The short-range attractive force between nucleons that overcomes the electrostatic repulsion between protons and holds the nucleus together, becoming repulsive at very short separations.
- Lepton
- A fundamental particle that does not interact through the strong interaction, for example the electron, the muon and their associated neutrinos.
- Baryon
- A hadron made of three quarks, for example the proton and the neutron.
- Strangeness
- A quantum property, given the value -1 for strange particles, that is conserved in the strong interaction but can change by 0, +1 or -1 in the weak interaction.
- Momentum
- The product of an object's mass and its velocity; a vector quantity, conserved in any interaction provided no external resultant force acts.
More in Quarks and Leptons
- Particle Colliders and Energy
- Baryons and Mesons
- Lepton Collisions
- Lepton Rules
- Neutrinos
- Strangeness
- The Quark Model
- Quarks and Beta Decay
All 17 lessons in Quarks and Leptons · All AQA AS-level Physics topics