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What is particle physics?

Particle physics, also called high energy physics (HEP), is a branch of physics that deals with the study of elementary particles and the fundamental relationships established between them.

Particle physics is based on the Standard Model, a quantum field theory that describes matter and the lack thereof based on the idea that elementary particles are irreducible packages of energy. Despite the fact that experimental tests have confirmed its predictions since its creation in 1970, it cannot yet be considered a complete theory due to a number of inadequacies. 

What are elementary particles?

Also known as fundamental particles, elementary particles are the smallest entities that constitute matter. As of now, it is thought that they are indivisible, are not made up of smaller particles, and do not have an internal structure.

At various stages in the history of physics, elementary particles have been thought to be other things. The atomic model held that the atom was the smallest particle of matter; moreover, the nuclear model suggested that the elements of the atom were indivisible. The standard model is the model of physics that is currently used.

What is the Pauli exclusion principle?

The Pauli exclusion principle is a rule of quantum mechanics that was set forth in 1925. According to this principle, there cannot be two fermions in the same quantum state (i.e., all with identical quantum numbers) within the same quantum system.​

What are the elementary particles?

Elementary particles are divided into two large groups, according to whether or not they are subject to the Pauli exclusion principle.

  • Bosons: these particles do not meet the Pauli exclusion principle; that is, two particles can occupy the same quantum state.
    The bosons that have been discovered so far are the following:
    • Photon.
    • W Boson.
    • Z Boson.
    • Gluon.
    • Higgs.
  • Fermions: they are particles of matter, like bosons, but unlike these, not all fermions are elementary particles; some are composed of other particles (such as quarks), which are themselves elementary. Fermions meet the Pauli exclusion principle; they also have spin and intrinsic angular momentum. Its distribution is governed by the Fermi-Dirac statistics, which counts states of occupation statistically.
    Fermions, in turn, are divided into two more groups:
    • Leptons: they can exist in isolation. The ones known so far are the following:
      • Electron.
      • Muon.
      • Tau.
      • Electron neutrino.
      • Muon neutrino.
      • Tau neutrino.
    • Quarks: unlike leptons, these cannot exist in isolation but are always found in the presence of other quarks, to which they are bound by gluons. The ones known so far are the following:
      • Up.
      • Charm.
      • Top.
      • Down.
      • Strange.
      • Bottom.

On the other hand, hadrons are particles composed of more elementary particles, and they are made up of quarks, antiquarks, and gluons. They can be:

  • Baryons: they contain three quarks, gluons, and antiquarks. Most of them are unstable except for nucleons (that is, protons and neutrons). Baryons are also fermions.
  • Mesons: they are made up of a quark, an antiquark, and a gluon. All of these are unstable, but despite that, they can be found in isolation. Mesons are also bosons.

In addition to these types of particles, there are also:

  • Hypothetical particles: these have been proposed theoretically, but their existence has not been proven practically.
  • Superpartner particles: these are suggested by the theory of supersymmetry and would be the symmetric particles of existing particles.
  • Quasiparticles: these are particular entities identified by condensed matter physics.

What research areas are there in particle physics?

The main goal of particle physics is to understand the fundamental structure of matter and its fundamental interactions. There are still many unanswered questions, such as the nature of dark matter, the quantum fluctuations of space-time, and the unification of the fundamental forces.

In pragmatic terms, particle physics has contributed to the development of technologies such as electronic devices based on semiconductors, for instance; in medicine, it has been of use in the development of radiation therapy and medical imaging technology. Despite the fact that this branch of physics examines the smallest elements of the universe, it is fundamental for understanding the largest known systems, so it is also closely related to astrophysics and cosmology.

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