# S-Cool Revision Summary

## S-Cool Revision Summary

#### Particle families

There are two main families of particle, the leptons and the hadrons.

#### Leptons

These are the lightest particles. Their name is derived from Greek: Lepton is small.

There are 3 types of lepton: the electron, muon and tau. In addition, each of these particles has an associated neutrino, and corresponding antiparticle, making a total of 12 family members. Leptons are truly fundamental.

Leptons are assigned a Lepton number (L). L = 1 for leptons and L = -1 for antileptons.

Hadrons are generally more massive than leptons. They are sub-divided into baryons (the most massive) such as protons and neutrons, and mesons (somewhat less massive) such as the pion and kaon.

#### Particle Numbers

In order to understand the interactions of these particles better they are assigned numbers as described below:

Charge (Q) is conserved in all interactions.

Baryons are assigned a Baryon number (B). B = 1 for baryons and B = -1 for antibaryons. Baryon number is conserved in all interactions.

Strange quarks possess a property called Strangeness (S). S = -1 for strange quarks and S = 1 for antistrange quarks.

#### Particle interactions

The 4 fundamental forces can be thought of as interactions between particles arising as a result of the exchange of virtual particles.

The four fundamental interactions are:

Interaction Exchange particles Range (m)
strong

gluon

(between quarks)

10-15
electromagnetic virtual photon
weak W+, W-, Z0 10-18
gravitational (graviton?)

Such exchanges can be represented on a Feynman diagram:

#### Beta decay

Beta decay is a result of the weak interaction. A down quark in the neutron emits a W- and changes into an up quark. The W- decays into an electron and an antineutrino.

#### Conservation Laws

In any interaction charge (Q), lepton number (L) and baryon number (B) are conserved. (L = 1 for leptons, L = -1 for antileptons. B = 1 for baryons, B = -1 for antibaryons)