A fermion is an elementary particle with half-integer spin.
A fermion is a type of elementary particle with half-integer spin, such as quarks and leptons. The electron, proton and neutron are also fermions, and they form matter as we know it, since they are the basic constituents of atoms.
Fundamental properties
Fermi–Dirac statistics
A theoretical framework used in quantum mechanics to describe the behavior of identical, indistinguishable particles, known as fermions. This statistic was developed by Enrico Fermi and Paul Dirac in the 1920s. It is mainly applied to particles that have half-integer spin, such as electrons, protons, and neutrons.
Pauli, exclusion principle
A direct consequence of the Fermi-Dirac statistic. It states that two identical fermions cannot occupy the same quantum state simultaneously. In other words, there cannot be two fermions in the same place with the same spin and the same quantum numbers.
Spin
An intrinsic property of subatomic particles that is related to their intrinsic angular momentum. Those with half-integer spin, such as fermions, obey the Fermi-Dirac statistic, while those with integer spin, such as the boson , obey the Bose-Einstein statistic.
The latter predicts the phenomenon of Bose-Einstein condensates , the collapse of a set of extremely cooled bosons. The half-integer property of spin means that its values are 1/2, 3/2, etc. This is in contrast to bosons, which have integer spin values such as 0, 1, 2, etc.
Antiparticles
The counterparts of ordinary particles, but with opposite electric charge and other properties. For example, the antielectron (also known as the positron ) is the antiparticle of the electron. When a particle encounters its antiparticle , they can annihilate and convert to energy , according to Einstein's famous equation, E = mc 2 .
CPT Symmetry
A fundamental property that states that the laws of physics are invariant under the combination of three transformations: charge reversal (C), parity inversion (P), and time reversal (T) . This symmetry implies that the laws of physics are the same for a particle and its antiparticle, as well as for the process that occurs forward in time and its inverse.
CPT symmetry is one of the fundamental ideas in quantum field theory and has been widely confirmed by various experiments.
The Pauli exclusion principle and CPT symmetry are some of the fundamental properties of the fermion.
Leptons
Leptons are a class of subatomic particles that are not composed of smaller ones. Along with quarks , leptons are the basic constituents of matter according to the standard model of particle physics . They are fermions and obey the Fermi-Dirac statistics.
The four types of known leptons are the electron , the muon, the tauon and their corresponding associated neutrinos : the electron neutrino , the muon neutrino and the tauon neutrino . Each has an elemental electrical charge of -1 (for charged leptons, i.e. the electron, muon and tauon) or 0 (for neutrinos).
Electron
The best known lepton. It has an electrical charge of -1 and is commonly found in atoms, orbiting around the atomic nucleus.
Neutrino
Neutral and very low-mass particles that interact weakly with matter. An interesting feature of neutrinos is their ability to change from one type to another as they travel through space, a phenomenon known as neutrino oscillation .
Muon
A particle similar to the electron but with a mass approximately 200 times greater. It is formed in the decay processes of more massive particles, such as pions, and quickly decays into electrons and neutrinos.
Tauon
The most massive lepton of the three. Its mass is approximately 3500 times greater than that of the electron. Like the muon, the tauon is unstable and rapidly decays into lighter particles, including electrons and neutrinos.
Neutrinos have been the subject of intense research in recent years. For example, ice neutrino experiments, such as IceCube , use large volumes of Antarctic ice to detect high-energy cosmic neutrinos, providing insights into extreme astrophysical phenomena such as supernovae and black holes. Additionally, neutrino oscillation has been observed and measured in experiments such as Super-Kamiokande , confirming the idea that these particles have mass and can change from one type to another as they travel through space.
Quarks
Quarks are elementary particles that make up the hadron , including the proton and the neutron , which in turn form the atomic nuclei. They are fermions and are classified as fundamental constituents of matter.
There are six different types of quarks, each with a color charge that can be red, green or blue, or its corresponding anticolor (antired, antigreen or antiblue). They are the only particles known to experience the strong interaction, one of the four fundamental forces of nature, mediated by particles called gluons , which also carry color charge. Because of this interaction, quarks are confined within hadrons and are never observed in isolation.
Quarks also experience the weak interaction, mediated by force-carrying particles called W and Z bosons, which is responsible for some type of radioactive decay , such as beta decay .
Finally, quarks experience the gravitational interaction, which is the weakest force of all fundamental interactions. However, in the realm of subatomic particles and nuclear interactions, gravity is generally insignificant compared to the other forces and can be ignored in most cases.
Fermions can appear as a particle or as a wave, depending on the situation.
Quantum and theoretical aspects
Fermions exhibit a number of fascinating quantum and theoretical phenomena that have been widely studied.
Wave-particle duality
In certain situations, fermions can exhibit both particle properties (defined position, momentum) and wave properties (interference, diffraction). This duality is a fundamental characteristic of quantum mechanics and is manifested in experiments such as the double slit.
Quantum tunneling effect
Fermions can cross potential barriers that would classically be impenetrable. This effect is due to the probabilistic nature of quantum wave functions and has applications in various fields, such as semiconductor physics and quantum electronics.
Quantum hall effect
A quantum phenomenon that occurs when a magnetic field perpendicular to an electric current is applied in a two-dimensional conductive material. The fermions in the material exhibit a quantized electrical resistance, leading to a series of plateaus in the Hall diagram as a function of the applied magnetic field. This effect is a manifestation of the topological properties of fermions and has important applications in metrology and quantum electronics.
Quantum entanglement effect
The state of one fermion is intrinsically linked to that of another, even if they are separated by large distances. This phenomenon, predicted by quantum mechanics, has been experimentally verified and has fundamental implications in quantum information theory and quantum cryptography.
Supersymmetry
A theoretical symmetry that proposes that each fermionic particle has a bosonic counterpart and vice versa. Supersymmetry is a fundamental idea in particle physics theory beyond the Standard Model and has been explored through high-energy experiments such as the Large Hadron Collider (LHC) .
string theory
A theoretical framework that describes fundamental particles as one-dimensional string vibrations rather than dimensionless points. It is a quantum theory of gravity that seeks to unify all the fundamental forces of nature and is one of the most promising approaches to physics beyond the standard model.