Loading...
Every particle physicists have ever detected sorts neatly into just two families, based on a single question: does it feel the strong nuclear force? That distinction, combined with a handful of conserved counting numbers, explains why the proton has never once been observed to decay.
What you'll be able to do
A is built from quarks and feels the strong force; a (like the electron or muon) is fundamental and never feels the strong force. Hadrons split into (three quarks, ) and (quark-antiquark, ).
Tip — Because the proton is the lightest baryon, baryon number conservation forbids its decay — there is no lighter baryon for it to decay into.
At this level, three quark flavours are needed: up (), down () and strange (), each with an oppositely-charged antiquark.
The strange quark carries strangeness . Strangeness is conserved in strong and electromagnetic interactions, but can change in weak interactions — the signature of a weak process.
Tip — Whenever a proposed reaction conserves charge and baryon number but not strangeness, don’t call it forbidden — call it weak.
Equation recap
Common mistakes to avoid
Key takeaways
Test yourself
Ready to lock in Classification of Particles and Quarks? Pick a mode and earn XP & Dobloons.