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Particle Physics Fundamentals
Introduction to Particle Physics

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Over the 20th century, one of the most startling things discovered was the diverse number of particles that exist in the universe. Though particle physics has existed for just over a century, the concept goes back to the ancient Greeks, who predicted that matter could be broken down into fundamental, indivisible particles (a concept known as atomism).

The Standard Model of Particle Physics

The Standard Model of Particle Physics is at the core of modern physics. In this model, the four fundamental forces of physics are described, along with the particles that mediate these forces - gauge bosons.

Groups of Particles

If there's one thing that particle physicists seem to enjoy, it's dividing up particles into groups. Here are a few of the groups which particles exist in:

Elementary Particles
- Fermions - particles with half-integer spin
  - Quarks - 6 flavors exist
  - Leptons - 6 types, and their antiparticles
    - Electron
    - Electron Neutrino
    - Muon
    - Muon Neutrino
    - Tau
    - Tau Neutrino
- Bosons - particles with integer spin
  - Photon
  - W Boson
  - Z Boson
  - Gluon
  - Graviton
  - Higgs Boson
Composite Particles
- Hadrons
  - Baryons (fermions)
    - Nucleons - protons & neutrons
    - Hyperons - short-lived particles composed of strange quarks
  - Mesons (bosons)
- Atomic Nuclei - protons and neutrons form together to create the atomic nucleus
- Atoms - includes the atomic nucleus and the surrounding "electron cloud"
- Molecules - formed when groups of atoms bond together

A Note on Particle Classification

It can be hard to keep all the names straight in particle physics, so it might be helpful to think of the animal world, where such structured naming is more natural to us. Humans are primates, mammals, and also vertebrates. Similarly, protons are baryons, hadrons, and also fermions.

The unfortunate difference is that the terms tend to sound similar to each other. Confusing bosons and baryons, for example, is far easier than confusing primates and invertebrates. The only way to really keep these different particle groups separate is to just carefully study them and try to be careful about which name is being used.