The W boson
Part 1: The Standard Model
Lisi Goodlett

The Standard Model

Fermions and Bosons

Leptons

Baryons

Mesons

Forces and Interactions

Gauge Bosons

Fermions and Bosons

All subatomic particles can be classified as either fermions or bosons

Fermions – spin is ½ integral

Include leptons and baryons

Bosons – spin is integral

Include mesons and gauge bosons

Leptons
particles that have no strong interactions.
The six known types of leptons are shown. There are also six anti-lepton types, one for each lepton.

Baryons:
are particles made from a basic structure of three quarks (and anti-baryons from three antiquarks) and are bound together by their strong interactions.

Mesons
Mesons are particles with a basic structure of one quark and one antiquark. They are also bound by their strong interactons.

Forces and Interactions

All forces between objects are due to interactions. All particle dacays are due to interactions. The four types fundamental interaction processes responsible for all observed processes are:

Strong interactions, responsible for forces between quarks and gluons and nuclear binding. (Strength = 1, Range = 10^-15).

Electromagnetic interactions, responsible for electric and magnetic forces. (Strength = 10^-2, Range = infinite).

Weak interactions, responsible for the instability of all but the least massive fundamental paricles in any class. (Strength = 10^-5, Range = 10^-18).

Gravitational interactions, responsible for forces between any two objects due to their energy (which includes their mass). (Strength = 10^-39 Range = infinite).

Gauge Bosons (Force Carriers)

Each type of interaction has a characteristic set of force carrier particles associated with it.

Gluons are the carrier particles of strong interactions.

Photons are the carrier particles of electromagnetic interactions.

W and Z bosons are the carrier particles of weak interactions.

It is assumed that there should also be a force carrier for gravitational interactions, a graviton, though there is no experimental evidence for it.

Interactions and their carriers

To come in Part 2...

The W boson was only discovered experimentally in 1983.

Before its discovery, its mass was predicted, with reasonable accuracy, by the electroweak theory.

The W boson (Part 1) The Standard Model Lisi Goodlett

Horst Wahl

2003-10-08T14:35:15