6.4.2 Fundamental particles

Okay so this section is all about how we group different particles into different...well....into different groups. We have matter and antimatter and leptons and and baryons and kaons and pions and mesons and hadrons and quarks and so on...

Antimatter
(This is the prediction that) every particle has a corresponding antiparticle and they completely destroy each other in annihilation if they meet where the masses of both particles are converted into a high-energy pair of photons. An antiparticle has the opposite charge to its corresponding particle and the exact same rest mass:

• electron - positron
• proton - antiproton
• neutron - antineutron
• neutrino - antineutrino

Fundamental particles
A fundamental particle is a particle with no internal structure (therefore it cannot be divided into smaller bits). 


Hadrons and leptons
Subatomic particles are classified into two families, hadrons and leptons:

• Hadrons
• particles and antiparticles affected by the strong nuclear force
• examples include protons/neutrons/mesons
• They also experience the electromagnetic force if charged
• They decay by the weak nuclear force
• All hadrons are made up of quarks
• Leptons
• Particles and antiparticles not affected by the strong nuclear force
• examples include electrons, neutrinos, and muons
• leptons experience the electromagnetic force if charged
• They are fundamental particles so they do not decay

Quarks

All hadrons are made up of quarks. Quarks and leptons are the building blocks of matter (they are the fundamental particles). Any particle that contains a quark is a hadron. The standard model of elementary particles requires 6 quarks (up, down, charm, strange, top, and bottom) and 6 antiquarks. all quarks have a charge Q that is a fraction of e. For example, an up quark has a charge of 2e/3. 

All hadrons experience the strong nuclear force. Individual quarks are bound together within the particle by the attractive strong nuclear force.

A proton consists of 3 quarks, up up down (uud). The total charge must equal e. A neutron also consists of 3 quarks , up down down (udd). The total charge is 0.


Mesons and baryons
Baryons are any hadrons made with a combination of 3 quarks. Mesons are the hadrons made with a combination of a quark and an anti-quark.


Neutrinos
Neutrinos are quite mysterious fundamental particles that carry no charge and may have a tiny mass. Its existence was predicted in order to explain beta decay in terms of conservation laws. Each neutrino has a corresponding antineutrino. There are 3 types of neutrino:

• the electron nuetrino
• the muon neutrino
• the tau neutrino

Beta decay
Beta radiation is the emission of either electrons (β⁻) or positrons (β⁺). The force responsible for beta decay is the weak nuclear force.

• Beta minus decay
• a neutron in an unstable nucleus decays into a proton, an electron, and an electron antineutrino:
• n --> p + e +  ̅ν_e
• Quark transformation: udd --> uud ∴ d --> u + e +  ̅ν_e
• It is important to realise that nucleon and proton number and conserved (as is total charge)
• Beta plus decay
• A proton decays into a neutron, a positron, and an electron neutrino
• p --> n + e + ν_e
• Quark transformation : uud --> udd ∴ u --> d + e +  ν_e
• Charge is conserved and so is the proton/nucleon number