QCEphysics

The Standard Model

define the concept of an elementary particle and antiparticle

- The Standard Model is a theory describing three of the four known fundamental forces in the universe, as well as classifying all known elementary particles

• An elementary particle is a particle with no substructure, and thus not composed of other particles

▪ Lepton

▪ Quark

▪ Gauge bosons

▪ Higgs bosons

• An antiparticle is a particle that has the same mass and opposite charge and/or spin as a corresponding particle

▪ Particles and antiparticles annihilate each other, giving off gamma rays

recall the six types of quarks

- Colour charge

○ Quarks - red, green, blue

○ Antiquarks - antired (cyan), antigreen (magenta) or antiblue (yellow)

define the terms baryon and meson

- Hadrons are particles composed of quarks and gluons

- Mesons are a subatomic particle composed of one quark and one antiquark, held together by the strong nuclear force.

- Baryons are composite subatomic particles made up of three quarks or antiquarks (antibaryon) and held together by the strong nuclear force.

○ Neutron - udd, charge 0

○ Proton - uud, charge +1

○ Omega minus - sss, charge -1

○ Lambda - uds - charge 0

recall the six types of leptons

recall the four gauge bosons

- Gauge bosons are mediating particles that govern particle interaction and the mediation of the four fundamental forces.

○ Photons

○ W boson

○ Z boson

○ Gluon

describe the strong nuclear, weak nuclear and electromagnetic forces in terms of the gauge bosons

Strong nuclear force

- Only quarks within nucleons experience the strong nuclear force

- Acts over extremely small distance (~10-15m)

- Force increases as particle separation increases

- Gluon is mediating particle

Electromagnetic force

- Hold electrons in atoms and binds matter as molecules.

- Causes protons in nucleus to repel each other

- Operates over infinite distance

- Photon is mediating particle

Weak Nuclear force

- Responsible for slow nuclear processes such as radioactive decay and fusion reactions

- W and Z bosons are mediating particles

Gravitational force

- Not yet included in Standard Model

- Operates over infinite distance

- Gravitron is its infinite particle

contrast the fundamental forces experienced by quarks and leptons.

- Strong nuclear - quarks with nucleons

- Electromagnetic - quarks and leptons with charge

- Weak nuclear - all quarks and leptons

Students should be able to recall, describe and explain the properties of the
nuclear model of the atom and strong nuclear forces (Unit 1 Topic 2: Ionising radiation and nuclear reactions).

Students should be able to recall, describe and explain the properties of
electromagnetic forces (Unit 3 Topic 2: Electromagnetism).