Classification of particles

What are hadrons?

Particles made up of quarks only

What are the two types of hadrons?

Baryons(and anti baryons) and mesons

What are baryons?

Particles made from 3 quarks

What are mesons?

Particles made from quarks and antiquarks

What are some examples of baryons?

Protons and neutrons

What is a common feature to all baryons?

They unstable and will decay into protons

(Protons are the only stable baryons)

What are antibaryons?

• antiparticles of protons and neutrons

• these and baryons will annihilate each other

• so antibaryons are not found in normal matter

What is a baryon number?

The number of baryons

• Baryons have a number = +1

• Antibaryons have a number = -1

• This number is always conserved in any interaction

• Mesons have a number of = 0 as it is not a baryon

Mesons

• second type of hadron

• All are unstable

• Baryon number = 0

• Ligher mesons = pions

• Heavier mesons = kaons

What are leptons?

• fundamental particles

• E.g. electrons, muons and tau

• Electrons are stable but muons and tau are unstable (decay into electrons)

• Muons and tau are heavier versions of electrons

• All leptons come with their own neutrino (ve, vm, vt)

What are neutrinos?

• A type of lepton

• zero or almost zero mass or electric charge

What do all lepton have in common?

• they all have a charge of +1

• their lepton numbers must be calculated separately

• they all come with their own neutrino

• they are fundamental particles

Why are photons an exception in the classification system?

• no mass

• no charge

• no baryon number

• no lepton number

• it does have energy

• they are denoted by y