The Standard Model of Particle Physics - Part 1: An Introduction to the Model

By Prithve Shekar


Ever since the era of modern physics began in the early 1900s, physicists have been trying to ascertain the fundamental structures of matter. Over the years many theories have been developed and disproved, but a few remained. The combination of these theories, and their continued development is what has given us the Standard Model.



Now, this may seem like a mere table of quantum particles, and nothing more. However, that is not what it is. Much like the periodic table of chemistry, the standard model represents a sliver of what is known in the field, but is also an excellent representation of fundamental ideas.

Now, what exactly is on this table? As you can see, the table is divided into 4 distinct sections, the quarks, leptons, gauge bosons, and scalar bosons. Each of these are different types of fundamental particles, that have different sets of properties, and participate in different reaction. The quarks and leptons are collectively termed ‘fermions’, and the gauge and scalar bosons are known simply as ‘bosons’. The fermions constitute matter, while the bosons are essentially force carriers, that propagate the fundamental forces (The higgs is an exception, we’ll talk about it in what may be a part two of this article). Of the four fundamental forces, three have had their bosons discovered, with gravity being the exception.


Fermions

These particles are the building blocks of matter, giving it its properties and mass*. They’re divided into three generations, where the lightest (and most stable) particles make up the first generation, with heavier particles in succeeding generations. These heavier particles quickly convert into their lighter counterparts through a process known as ‘decay’.

The quarks in the group are particles which make up some familiar particles like the proton. Two up quarks, and one down quark make a proton, while two down quarks and one up quark make a neutron. These specific particles are baryons, which are particles made up of three quarks.

The leptons in the group contain the more commonly known electron, along with its cousins. The electron, muon, and tau are the main constituents. Their neutrinos are particles which have the same mass, but no charge


Bosons

Bosons carry the four fundamental forces, as previously stated. The gluon is responsible for the strong force, which keeps the nucleus together in an atom. The W and Z bosons are responsible for the weak force, which is responsible for beta-decay processes. The photon is responsible for the electromagnetic force. Yet to be discovered is the fundamental particle for gravity, dubbed the ‘graviton’.


Antiparticles

While not shown in the image, antiparticles and antimatter actually exist, are not limited to the realm of science fiction. Every single particle has a corresponding antiparticle, which has the exact same mass, but all of their properties are reversed. When a particle comes into contact with an antiparticle, they annihilate, converting their masses into energy.

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