What is The Standard Model of Particle Physics?

The Standard Model is the most widely accepted current theory of particle physics. It explains the relationships between fundamental particles (aka: elementary particles) and the four fundamental forces of nature (strong force, weak force, electromagnetism, and gravity). The Standard Model was a collaborative effort developed by many scientists throughout the latter half of the 20th century. The current version of the theory emerged in the mid-1970s after confirmation of the existence of quarks.

Fundamental Particles of the Standard Model

Fermions

Bosons

Quarks

Gauge Bosons

Scalar Boson

Up Quark

×3 colors:
red, blue, green

Charm Quark

×3 colors:
red, blue, green

Top Quark

×3 colors:
red, blue, green

Gluon

8 Gluon Colors

There are 8 gluons in total—4 inverse pairs.

Gluons carry both color and anticolor charges between quarks, so the antiparticle of any gluon is simply another of the gluons. e.g. The antiparticle of the red-antiblue gluon is the blue-antired gluon.

Higgs Boson

Down Quark

×3 colors:
red, blue, green

Strange Quark

×3 colors:
red, blue, green

Bottom Quark

×3 colors:
red, blue, green

Photon

Leptons

Electron

Muon

Tau

W± and Z0

Electron Neutrino

Muon Neutrino

Tau Neutrino

Graviton*

What is a Fundamental Particle?

Also known as elementary particles, fundamental particles are the basic building blocks of the universe; fundamental particles are particles that the standard model predicts to have no substructures. Atoms were once presumed to be the fundamental particles of matter. Growing up, many of us learned that atoms are actually composed of three subatomic particles— protons, neutrons, and electrons. While electrons are in fact indivisible fundamental particles, protons and neutrons can be further broken down into even smaller particles. There are also a number of fundamental particles that can only be observed in very high-energy environments. A particle containing two or more fundamental particles is a composite particle. Protons and neutrons are actually composite particles.

There are sixteen* distinguishable types of fundamental particles (*seventeen if we count the Graviton, which has yet to be discovered). These sixteen particle types can be further consolidated into four major groups- Quarks, Leptons, Gauge Bosons, and a Scalar Boson. Quarks and Leptons are classified as Fermions (Matter Particles) and Gauge Bosons and the Scalar Boson are classified as Bosons (Force Particles). See chart above.

Fermions & Bosons

All elementary particles are either Fermions— matter particles or Bosons— force particles. In particle physics the 'spin' of a particle relates to the type of statistics that particle obeys. Fermions have half-integer spin and follow Fermi-Dirac Statistics. Bosons have an integer (whole number) spin and follow Bose-Einstein Statistics.

Don’t let these statistics intimidate you; the main point to grasp is this: Fermi–Dirac Statistics apply to particles that obey the Pauli Exclusion Principle. Particles with half-integer spin follow the Pauli Exclusion Principle and particles with integer spin do not. Fermions (matter particles) are particles with half-integer spin, therefore they follow the Pauli Exclusion Principle and are governed by Fermi–Dirac Statistics. Bosons (force particles) on the other hand, have integer spin, so they are not subject to the Pauli Exclusion Principle and do not follow Fermi–Dirac Statistics.

The Pauli Exclusion Principle states that no two identical particles with half-integer spin can occupy the same quantum state simultaneously. In other words, no two Fermions (matter particles) can occupy the exact same quantum state at the same time.

Bose-Einstein Statistics on the other hand apply to particles that do not obey the Pauli Exclusion Principle- i.e.particles with integer spin- i.e. Bosons. Bosons (force particles), do not abide by the Pauli Exclusion Principle, which means that two or more Bosons can occupy the same quantum state at once.

So, what all of this means in summation is that bosons can overlap and coexist with other bosons while fermions cannot. This explains why fermions act as solid building blocks of matter, while bosons manifest as observable phenomena such as light, magnetism, gravity, etc. which are all derivatives of the four fundamental forces.

Particle Vocab:

Fermi–Dirac Statistics describe particle distribution in systems comprising many identical particles that all obey the Pauli exclusion principle. Essentially this means that Fermi–Dirac statistics explain the laws that govern how fermions behave when in large groups (remember all particles that ‘obey the Pauli exclusion principle’ have half-integer spin and are therefore fermions).

Bose-Einstein Statistics describe particle distribution in systems comprising many identical particles that do not obey the Pauli exclusion principle. Essentially this means that Bose-Einstein statistics explain the laws that govern how bosons behave when in large groups (remember all particles that do not ‘obey the Pauli exclusion principle’ have integer spin and are therefore bosons).

The Pauli Exclusion Principle

The Pauli Exclusion Principle states that no two identical particles with half-integer spin (fermions) can occupy the same quantum state simultaneously.

Spin

The spin of a particle is its intrinsic angular momentum– the contribution to the total angular momentum, which is not due to the orbital motion of the particle– In other words, the spin of a particle determines how that particle affects the momentum when it is part of a system of many particles.