Unit 1 section 1 Classification of particles

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hadrons

hadron: a particle that is affected by the strong nuclear force. consists of baryons and mesons.

baryons: a hadron made up of three quarks, like protons and neutrons, and antiprotons and antineutrons.

meson: a hadron made up of a quark and an antiquark, like pions and kaons, and antipions and antikaons.

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baryons

all baryons except the proton are unstable so all baryons decay into a proton.

baryon number: the number of baryons in a particle.

the proton and neutron and all other baryons have a baryon number of B=+1.

antibaryons have a baryon number of B=-1

all other particles that aren't baryons have a baryon number of B=0.

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mesons

mesons are pions and kaons. all mesons are unstable and have a baryon number of B=0.

mesons interact with baryons via the strong force.

pions are the lightest mesons. there are three versions of the pion. PIE+, PIE0 and PIE-.

kaons are the heavy and more unstable mesons, they exist as K+, K0 and K-.

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leptons

hadrons feel the strong force, while leptons can only interact via the weak force/interaction.

leptons are:

- electron

- muon

and their respective neutrinos.

lepton number: the number of leptons in a particle. count seperately for different types of leptons.

electrons have an electron lepton number of +1

muons have a muon lepton number of +1

their respective neutrinos have the same lapton numbers.

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conservation of lepton and baryon numbers

both Baryon and both types of lepton number need to be conserved for a particle interaction to happen.

to check this just work out the numbers on each side of the reaction.

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