Particles are everywhere

We know that matter consists of atoms which in turn consists of neutrons, protons and electrons. There are also photons, that carry electromagnetic energy. The electron appears to be a fundamental particle since we never see it decay into something else. However, the neutrons and protons seem to have some internal structure. A neutron, if left on its own, can disintegrate[1] into a proton and an electron in nearly 15 minutes:

    \[n \rightarrow p + e^{-} + \bar{\upsilon }_{e}\]

The \bar{\upsilon }_{e} particle is called anti-neutrino. It is the antiparticle of neutrinos(more on this later) that are presumably massless and uncharged point-like particles which appear mostly in processes involving electrons (or antielectrons). The electrons and neutrinos do not appear to have any internal structure (unlike protons and neutrons) and are thus classified as some of the “elementary particles”.

Experiments such as the Large Hadron Collider and studies of cosmic rays have resulted in the discovery of even more elementary particles. They were named pions, muons, kaons, tau etc. until we ran out of greek letters! All of these particles present a challenge to the physicists because many of them exist for miniscule durations and at high energies which are not easily attainable. However based on what we know(and we know quite a bit), there are certain patterns in their properties and behaviour. These patterns make them easier to sort into categories.

The standard Model

The standard model is widely accepted as the most fundamental level of classification of elementary particles we have yet achieved. This model assumes that at the heart of everything there are certain elementary particles which can interact with each other according to certain conservation laws. There are basically two kinds of particles, leptons and quarks (collectively known as the Fermions). The interactions among them(forces) are modeled by carrier particles, known as Bosons1.

Thus, the standard model divides elementary particles into two categories, Bosons(e.g. photons, W and Z bosons etc.) and Fermions(electrons, quarks etc.).The Fermions are further categorized into Leptons and Quarks.

standard model: Fermions and Bosons

It also lists their properties and interactions. The interactions are governed by Conservation Laws. In this way, the standard model is a theory in itself[2]. Although there are certain anomalies in this model but for the sake of our discussion we assume it is correct. In the subsequent posts, I shall discuss more about Fermions, Bosons and their spin. I shall update the list below as I go along:

  1. Laws of Conservation
  2. Fermions: Hadrons and Leptons
  3. Bosons
  4. Spin and Pauli’s Exclusion Principle
  5. Types of interactions(fundamental forces)
  6. The three generations of matter

In the meanwhile, you can check out particleadventure.org. I love this website and they have an app too. Happy learning!

ยน Unlike Newtonian Physics, we do not treat forces as anything different from particles. Essentially all particles are considered to be the manifestation of some field. Photons are thus, equivalent to electromagnetic fields and particles have mass due to Higgs field.

Disclaimer: All of the information provided above is a simplification. Most of these topics require understanding of advanced concepts and involve mathematical difficulties in explaining them theoretically. I recommend you refer to a standard textbook such as Introduction to Elementary Particles by David Griffiths for clear and precise explanations.

Particle Physics: Particles and the Standard Model
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