Elementary (Fundamental) Particles & The Standard Model

Fundamental Particles or Elementary Particles

Fundamental or elementary particles are subatomic particles that are not composed of other particles. Thus, they cannot be subdivided into smaller components. They have no known internal structure.

Subatomic particles can be either elementary or composite. Composite particles are made up of multiple elementary particles.

The Standard Model of particle physics is the best current theory explaining the fundamental particles (the most basic building blocks of the universe) and the fundamental forces that govern their interactions, except for gravity. It explains how particles called quarks (which make up protons and neutrons) and leptons (which include electrons) make up all known matter.
The Standard Model of Particle Physics consists of 17 fundamental particles. Based on their spin, they are divided into two main types: fermions and bosons. They are the smallest and basic building blocks of matter and energy.

Spin (a quantum mechanical property) is an intrinsic form of angular momentum carried by elementary particles. It’s a fundamental property, meaning it’s inherent to the particle and doesn’t arise from the particle’s motion.

Fermions include Leptons and Quarks. They are fundamental particles which make up matter in the universe. They have odd half-integer spins (1/2, 3/2, and 5/2, but not 2/2 or 6/2).
Fermions obey the Pauli exclusion principle, hich states that no two or more identical fermions can occupy the same quantum state simultaneously. Due to this, fermions are solitary in nature.

Leptons are fundamental particles that do not experience a strong nuclear force.
There are six leptons: electron, muon, tau, and their corresponding neutrinos.

Electrons are negatively charged particles orbiting the nucleus of an atom.
Electron is the lightest stable subatomic particle known and is the most well-known lepton.

A muon is an elementary particle similar to an electron but with much greater mass.
Muons are negatively charged. They are unstable and decay into other particles within microseconds.

The tau particle is the heaviest of the three charged leptons (electron, muon, tau).
Like muons, negatively charged tau particles are unstable and decay rapidly into other particles within 290 femtoseconds.

Neutrinos are tiny particles with no electric charge (neutral) and very little mass. They are the lightest of all the subatomic particles that have mass. They are the most abundant particles in the universe.
They are called “ghost particles” due to their extremely weak interactions with matter, making them hard to detect (elusive). They interact only via the weak nuclear force and gravity.
Neutrinos are formed through various processes, such as nuclear fission in nuclear reactors, fusion reactions inside the sun, radioactive decay, cosmic rays, supernova explosions, and particle accelerators. Even bananas emit neutrinos due to the natural radioactivity of potassium.
Neutrinos come in three types called flavours: electron neutrino, muon neutrino, and tau neutrino.

Quarks combine to form composite subatomic particles called hadrons.
Quarks carry a type of charge known as “colour charge,” which is related to the strong nuclear force that the quarks experience. There are three types of colour charges (red, green, and blue), and quarks combine to form colour-neutral particles.
Due to the strong force, quarks are always confined within hadrons; they cannot exist independently.
In terms of electric charge, they can be positively and negatively charged.
There are six types (flavours) of quarks based on charge: up (lightest of all quarks), down, charm, strange, top (heaviest of all quarks and the most massive subatomic particle known), and bottom.

Hadrons are composite particles made of quarks held together by the strong nuclear force, mediated by gluons. They are divided into two main groups:
1. Baryons: comprises three quarks (e.g., protons and neutrons, the components of atomic nuclei).
2. Mesons: comprises a quark-antiquark pair (e.g., pions).

Bosons are fundamental particles that mediate forces between other particles. They are energy and force carriers throughout the universe.
Bosons do not follow the Pauli exclusion principle so that multiple bosons can occupy the same quantum state. This allows them to form a Bose-Einstein condensate, a state of matter where extremely cold atoms act as a single entity.
They have integer spin values (0, 1, 2, etc.).
They fall into two categories: gauge bosons and scalar bosons.

Gauge bosons are particles with a spin of 1. They include:
1. Photons: They are the constituent particles of light & the mediators of the electromagnetic force.
2. Gluons: They mediate the strong nuclear force and bind quarks together to form composite particles like protons and neutrons, holding the nucleus together.
3. W and Z Bosons: They mediate the weak nuclear force and help in radioactive decay.

Nobel prize-winning physicist Peter Higgs, who recently passed away, proposed the existence of the Higgs Boson in 1964. The Higgs Boson could lead to discoveries of new particles or reveal connections between forces we never knew existed.
Scientists confirmed the existence of Higgs Boson in 2012 through experiments at the Large Hadron Collider (LHC — produces collisions with high energies to replicate conditions similar to the Big Bang) at CERN in Switzerland. This discovery led to the 2013 Nobel Prize in Physics awarded to Higgs and Englert.

The Higgs Boson, also called the God particle, is the fundamental force-carrying particle of the Higgs field (a scalar field that permeates all of space). It is responsible for granting other particles, such as electrons and quarks, their mass.

According to the Standard Model of Particle Physics, particles gain mass by interacting with the Higgs field. Without it, atoms wouldn’t stick together, and there would be no stars, planets or us.
The Higgs field is hypothesised to exist everywhere in space, even in a vacuum, and has a non-zero value.
Particles like photons interact weakly with the Higgs field and have no mass.
Particles like quarks interact strongly with the Higgs field and acquire mass.