The Standard Model

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 The Standard Model of Particle Physics is scientists’ current best theory to describe the most basic building blocks of the universe. It explains how particles called quarks (which make up protons and neutrons) and leptons (which include electrons) make up all known matter. It also explains how force carrying particles, which belong to a broader group of bosons, influence the quarks and leptons.

The Standard Model explains three of the four fundamental forces that govern the universe: electromagnetism, the strong force, and the weak force. Electromagnetism is carried by photons and involves the interaction of electric fields and magnetic fields. The strong force, which is carried by gluons, binds together atomic nuclei to make them stable. The weak force, carried by W and Z bosons, causes nuclear reactions that have powered our Sun and other stars for billions of years. The fourth fundamental force is gravity, which is not adequately explained by the Standard Model.

There are 12 elementary fermions in the Standard Model, along with their antiparticles. There are six quarks and six leptons. Each classification is grouped in pairs, which form three generations which are given in order of increasing mass. Another characteristic of the first generation is that the particles do not decay.

The Standard Model includes 12 elementary particles of spin 1⁄2, known as fermions. According to the spin–statistics theorem, fermions respect the Pauli exclusion principle. Each fermion has a corresponding antiparticle.

Fermions are classified according to how they interact (or equivalently, by what charges they carry). There are six quarks (up, down, charm, strange, top, bottom), and six leptons (electron, electron neutrino, muon, muon neutrino, tau, tau neutrino). Each class is divided into pairs of particles that exhibit a similar physical behavior called a generation (see the table).

In the Standard Model, gauge bosons are defined as force carriers that mediate the strong, weak, and electromagnetic fundamental interactions.

The gauge bosons of the Standard Model all have spin (as do matter particles). The value of the spin is 1, making them bosons. As a result, they do not follow the Pauli exclusion principle that constrains fermions: thus bosons (e.g. photons) do not have a theoretical limit on their spatial density (number per volume).

The Higgs particle is a massive scalar elementary particle theorized by Peter Higgs in 1964, when he showed that Goldstone's 1962 theorem (generic continuous symmetry, which is spontaneously broken) provides a third polarisation of a massive vector field. Hence, Goldstone's original scalar doublet, the massive spin-zero particle, was proposed as the Higgs boson, and is a key building block in the Standard Model. It has no intrinsic spin, and for that reason is classified as a boson (like the gauge bosons, which have integer spin).

 Despite its success at explaining the universe, the Standard Model does have limits. For example, the Higgs boson gives mass to quarks, charged leptons (like electrons), and the W and Z bosons. However, we do not yet know whether the Higgs boson also gives mass to neutrinos – ghostly particles that interact very rarely with other matter in the universe. Also, physicists understand that about 95 percent of the universe is not made of ordinary matter as we know it. Instead, much of the universe consists of dark matter and dark energy that do not fit into the Standard Model.

Standard Model Facts:

1. All ordinary matter, including every atom on the periodic table of elements, consists of only three types of matter particles: up and down quarks, which make up the protons and neutrons in the nucleus, and electrons that surround the nucleus.

2. The complete Standard Model took a long time to build. Physicist J.J. Thomson discovered the electron in 1897, and scientists at the Large Hadron Collider found the final piece of the puzzle, the Higgs boson, in 2012.

https://www.energy.gov/science/doe-explainsthe-standard-model-particle-physics

https://home.cern/science/physics/standard-model

https://www.quantamagazine.org/a-new-map-of-the-standard-model-of-particle-physics-20201022/

https://physics.info/standard/

https://www.sciencedirect.com/topics/chemistry/standard-model

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