Fundamental Particles: Quarks, Leptons, and Forces

Fundamental particles

Particles that cannot be broken down into anything smaller. They include quarks and leptons.

Two main types of fundamental particles

Quarks and leptons.

Fundamental particles

Particles that cannot be broken down into anything smaller. They include quarks and leptons.

Two main types of fundamental particles

Quarks and leptons.

Why are they called 'fundamental' particles?

Because they are the most basic building blocks of matter.

Quarks

Tiny particles that join together to make protons, neutrons, and other particles.

Three quarks you need to know

Up (u), Down (d), and Strange (s).

Charges of the up, down, and strange quarks

Up = +2/3, Down = -1/3, Strange = -1/3.

Proton composition

Two up quarks and one down quark (uud).

Neutron composition

One up quark and two down quarks (udd).

Leptons

Tiny particles that do not feel the strong nuclear force. Electrons and neutrinos are leptons.

Leptons to know for A-Level

Electron (e⁻), Electron neutrino (νₑ), Muon (μ⁻), Muon neutrino (ν_μ).

Charges of leptons

Electron and muon = -1, all neutrinos = 0.

Neutrinos

They help conserve energy and lepton number in particle interactions like beta decay.

Hadrons

Particles made of quarks, held together by the strong nuclear force.

Two types of hadrons

Baryons (3 quarks) and Mesons (1 quark + 1 antiquark).

Baryons

Hadrons made of 3 quarks. Examples: proton, neutron.

Baryon number of a baryon

+1 for baryons, -1 for antibaryons, 0 for everything else.

Mesons

Hadrons made of a quark and an antiquark. They help hold atomic nuclei together.

Examples of mesons

Pion⁺ (π⁺), Pion⁻ (π⁻), Kaon⁺ (K⁺), Kaon⁻ (K⁻).

Baryon number of a meson

0

Antiparticles

Particles that are like normal particles but with opposite charge and other properties.

Examples of antiparticles

Positron (e⁺), antiproton (p̅), antineutron (n̅), anti-neutrino (ν̅).

Annihilation

A particle and its antiparticle meet and turn into energy (usually gamma rays).

Pair production

A photon of energy turns into a particle and an antiparticle pair.

Exchange particles

Particles that carry forces between other particles.

Exchange particle for the electromagnetic force

Photon (γ).

Exchange particles for the weak nuclear force

W⁺, W⁻, and Z⁰ bosons.

Exchange particle for the strong force

Gluon.

Strong nuclear force

The force that holds protons and neutrons together in the nucleus.

Weak nuclear force

The force responsible for certain kinds of particle decay, like beta decay.

Photon

A particle of light. It carries energy and mediates the electromagnetic force.

Muon

A heavier version of the electron. It is a lepton.

Kaon

A meson that contains a strange quark. It has a property called 'strangeness' and decays via the weak interaction.

Strangeness

A quantum number related to the strange quark. It is conserved in strong interactions.

Lepton number

A rule that says lepton family types must be conserved in particle reactions.

Conservation laws

Rules that certain quantities (like charge, baryon number, and lepton number) stay the same before and after a particle interaction.

Quark content of a proton

uud (up, up, down).

Quark content of a neutron

udd (up, down, down).

Quark content of a pion⁺

u anti-d.

Quark content of a pion⁻

d anti-u.

Quark content of a kaon⁺

u anti-s.

Quark content of a kaon⁻

s anti-u.

Particles affected by the strong nuclear force

Quarks and hadrons (like protons, neutrons, and mesons).

Particles affected by the weak nuclear force

All particles (including neutrinos and leptons).

Particles that feel the electromagnetic force

Only charged particles.

Particles that feel the gravitational force

All particles with mass (but it's extremely weak at the particle level).