Introduction to the Standard Model and its components

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  Table of contents 

INTRODUCTION 

TO THE 

STANDARD MODEL

AND

ITS COMPONENTS


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The Standard Model explains how basic building blocks of matter interact, governed by four fundamental forces. It is the closest to a complete description of the universe at a fundamental level.

The Standard Model contains - Quarks, Leptons and Bosons.

MATTER PARTICLES:

Matter is made up of elementary particles which occur in two basic types - the quarks and the leptons. 
Before we go further, let me briefly explain what quarks and leptons are.

In simple terms, quarks are the subatomic particles that make up the protons and neutrons. On the other hand, leptons consist of electrons that are found orbiting around the nucleus of an atom.
This may not be the best way to define quarks and electrons, but for now, that will do. 

Now, each of these groups has 6 particles which are found in pairs as generations.

  • The first generation - consists of the lightest and most stable particles
  • The second and third generations - consist of heavier and less stable particles, which quickly decay to more stable ones i.e. the first generation. 
  • For e.g., Muon, which belongs to the second generation of leptons (see below), quickly decays to form electrons, which are found in the first generation.

QUARKS -

  • 1st Generation - Up Quark and Down Quark
  • 2nd Generation - Charm Quark and Strange Quark
  • 3rd Generation - Top Quark and Bottom/Beauty Quark

LEPTONS -

  • 1st Generation - Electron and Electron Neutrino
  • 2nd Generation - Muon and Muon Neutrino 
  • 3rd Generation - Tau and Tau Neutrino 
Now, what are neutrinos? 🤔

In simple words, neutrinos are neutral leptons, while electrons/muons/taus are negatively charged.

BOSONS:

Before we understand what Bosons are, let us understand what are the four fundamental forces.

FOUR FUNDAMENTAL FORCES -

There are four fundamental forces that are at work in the universe -
  • Strong force
  • Weak force
  • Electromagnetic force
  • Gravitational force
Each of these forces has its own ranges and strengths -
  • Gravitational force is the weakest of all but has an infinite range.
  • The Electromagnetic force is much stronger than the gravitational force and has an infinite range.
  • The weak force is stronger than the gravitational force but weaker than the other two forces. It has a short range.
  • The strong force, as the name suggests, is the strongest of all. It has a short-range too.
Each of these forces interacts with the universe through force carriers which are categorised as BOSONS.

FORCE CARRIERS are particles that act like messengers that exchange messages between particles.

Each fundamental force has its own corresponding boson. 
  • Strong Force - Gluon
  • Electromagnetic Force - Photon
  • Weak Force - W and Z bosons 
  • The Boson for gravitational force has not yet been found, however, the graviton is believed to be the boson for this force.

COMING BACK TO THE STANDARD MODEL:

  • The Standard Model includes the electromagnetic, strong and weak forces as well as their carrier particles i.e. bosons.
  • It explains how well these forces will act on all particles.
  • However, it does not include the Gravitational force as well as its hypothetical boson i.e. graviton.
  • It also includes the Quarks and Leptons.
  • It includes the HIGGS BOSON. (Explained in the next article!)
We have a Quantum theory that describes the micro world, and the General theory of relativity, that describes the macro world. It is very difficult to fit both these theories into a single framework. In fact, no one has managed to make these two theories mathematically compatible in the context of the Standard Model.

Luckily, the effect of gravity for the minuscule scale of particles is so weak that it is negligible. Only when matter is in bulk (like the human body or planets) does gravity dominate.

However, the Standard Model deals with particles that are very small. Thus, the Standard Model still works in spite of its inability to explain the gravitational force.

Some drawbacks of the Standard Model are -
  • Does not explain dark matter
  • Does not explain what happened to the antimatter after the big bang
  • Does not explain gravity
  • Does not explain why there are three generations of quarks and leptons with such different masses
Isn't there so much that's yet to be discovered?

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Feel free to ask/share anything additional in the comments section!

I am still learning Particle physics, but will try my best to answer your questions :)

Kindly let me know about any error here.

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With Warm Wishes,
Lavanya

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