Lesson summary
11.2.1 Fundamental Particles — AS PHYSICS 9702 notes: Describe quarks and leptons as fundamental particles and their properties.Fundamental — quarks are not made up of any other particles.Role — they make up other subatomic particles such as protons and neutrons.Hadrons — any par…
- Confinement
- Six flavours
- Six leptons
- Charged leptons
- Interact via
- No strong force
Section 1 of 7Quarks
Fundamental
- Fundamental quarks are not made up of any other particles.
Role
- Role they make up other subatomic particles such as protons and neutrons.
Hadrons
- Hadrons any particle made up of quarks, including protons and neutrons.
Confinement
- Confinement quarks have never been observed on their own, only in pairs or groups of three.
Six flavours
- Six flavours up, down, charm, strange, top and bottom.
Section 2 of 7Leptons
Fundamental
- Fundamental leptons are also fundamental particles and are not made of quarks.
Six leptons
- Six leptons electron, muon, tau and the three corresponding neutrinos.
- (electron, muon and tau)
Charged leptons
- Charged leptons the electron, muon and tau all have a charge of −1e.
- The muon and tau are similar to the electron but with a slightly larger mass.
Neutrinos
- Neutrinos three flavours with no charge and negligible mass, the most abundant leptons in the universe.
Section 3 of 7Forces felt by leptons
Interact via
- Interact via the weak interaction, the electromagnetic force and gravity.
No strong force
- No strong force leptons do not interact with the strong force.
Difference from quarks
- Difference from quarks quarks are fundamental but not leptons, because quarks interact through the strong force.
Section 4 of 7Antileptons
Antileptons
Antiparticles
- Antiparticles each lepton has an antilepton with the opposite charge.
Example
- Example the anti-muon μ+ is an antilepton.
Neutrinos
- Neutrinos the antineutrinos are the antileptons of neutrinos.
Identifying
- Identifying in a decay such as π+ → μ+ + neutrino, the pion is a meson, the muon neutrino is a lepton, and only the anti-muon is an antilepton.
Section 5 of 7More from the specification
More from the specification
Standard Model particle taxonomy
- Standard Model particle taxonomy grouping leptons, quarks, and gauge bosons provides a systematic means to categorize fundamental matter constituents.
Standard model elementary particles
- Fundamental matter particles comprise quarks and leptons (electron, muon, tau,
- (up, down, charm, strange, top, bottom)
- and their associated neutrinos), interacting via gauge bosons.
Quark composition of hadrons
- Hadrons are composite subatomic particles: baryons consist of three quarks,
- (e.g. protons: uud, neutrons: udd)
- while mesons consist of a quark-antiquark pair.
Beta decay and weak interaction
- Beta-minus decay converts a down quark into an up quark mediated by the weak W^- boson, preserving electric charge and lepton number.
- (d → u + e^- + anti-nu_e)
Baryon quark composition
- Baryon quark composition baryons consist of three quarks, while antibaryons comprise three antiquarks with opposite fractional charges.
Meson quark combination
- Meson quark combination formed by combining one quark and one antiquark, resulting in integer or zero total electric charge.
Beta-minus decay quark turn
- Beta-minus decay quark turn a down quark turns into an up quark, emitting an electron and an antielectron neutrino.
Decay equation
- An equation in nuclide notation with balanced nucleon and proton numbers.
Relative charge
- Charge compared with the fundamental charge 1.6 × 10−19 C.
Baryon
- Hadron made of three quarks.
Fundamental
- Fundamental quarks and leptons are fundamental particles with no known internal structure.
Hadrons
- Hadrons particles made of quarks; baryons contain three quarks and mesons contain a quark and an antiquark.
Nucleons
- Nucleons a proton is made of two up quarks and one down quark (uud) and a neutron of one up and two down quarks (udd).
Quark charge
- Quark charge an up quark has charge +2/3 e and a down quark has charge −1/3 e.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Quark | Fundamental particle that makes up hadrons. |
| Hadron | Particle made up of quarks. |
| Lepton | Fundamental particle that does not feel the strong force. |
| Fundamental particle | Particle not made up of any other particles. |
| Neutrino | Uncharged lepton of negligible mass. |
Section 7 of 7Exam technique
1
Saying quarks are leptons — quarks feel the strong force and leptons do not.
2
Saying protons and neutrons are fundamental — they are made of quarks.
3
Giving neutrinos a charge — they are neutral.
4
Naming only five leptons — there are six, three charged and three neutrinos.