Protons and neutrons, collectively known as nucleons, are not fundamental particles. Instead, they are composed of even smaller particles called quarks, bound together by the strong nuclear force. This force is mediated by particles called gluons.
Quarks come in six "flavors": up, down, charm, strange, top, and bottom. Each flavor has a different mass and charge.
| Quark | Charge | Mass (GeV/c2) |
|---|---|---|
| Up (u) | +2/3 | ~0.002 |
| Down (d) | -1/3 | ~0.004 |
| Charm (c) | +2/3 | ~1.27 |
| Strange (s) | -1/3 | ~0.1 |
| Top (t) | +2/3 | ~173 |
| Bottom (b) | -1/3 | ~4.18 |
Protons and neutrons are made up of up and down quarks:
Gluons are elementary particles that mediate the strong force, binding quarks together within protons and neutrons. Unlike photons, which carry the electromagnetic force, gluons also interact with each other, making the strong force highly complex.
In Quantum Chromodynamics (QCD), quarks and gluons carry a property known as color charge (analogous to electric charge in electromagnetism). Quarks come in three color charges (red, green, blue), while gluons act as carriers of color charge, ensuring quarks are bound within nucleons.
The behavior of quarks and gluons is described by the QCD Lagrangian, an equation that governs strong interactions: L = -¼FaμνFaμν + ∑f 𝗣f(i𝜵𝗮-mf)𝗣f
The Standard Model is a theoretical framework describing the fundamental particles and forces (except gravity) in the universe. It includes quarks, leptons, gauge bosons, and the Higgs boson. Protons and neutrons fall under the category of hadrons, particles composed of quarks.
Protons and neutrons are made up of quarks bound by the strong nuclear force, which is mediated by gluons. The complex interactions between quarks and gluons, governed by QCD, help form the stable particles we observe. Understanding the structure of nucleons provides insights into particle physics and the fundamental forces that govern our universe.