In the physical sciences, subatomic particles are particles much smaller than atoms. The two types of subatomic particles are: elementary particles, which according to current theories are not made of other particles; and composite particles. Particle physics and nuclear physics study these particles and how they interact. The idea of a particle underwent serious rethinking when experiments showed that light could behave like a stream of particles (called photons) as well as exhibiting wave-like properties. This led to the new concept of wave–particle duality to reflect that quantum-scale "particles" behave like both particles and waves (they are sometimes described as wavicles to reflect this). Another new concept, the uncertainty principle, states that some of their properties taken together, such as their simultaneous position and momentum, cannot be measured exactly. In more recent times, wave–particle duality has been shown to apply not only to photons but to increasingly massive particles as well.
Interactions of particles in the framework of quantum field theory are understood as creation and annihilation of quanta of corresponding fundamental interactions. This blends particle physics with field theory.
Composite subatomic particles (such as protons or atomic nuclei) are bound states of two or more elementary particles. For example, a proton is made of two up quarks and one down quark, while the atomic nucleus of helium-4 is composed of two protons and two neutrons. The neutron is made of two down quarks and one up quark. Composite particles include all hadrons: these include baryons (such as protons and neutrons) and mesons (such as pions and kaons).
In special relativity, the energy of a particle at rest equals its mass times the speed of light squared, E = mc2. That is, mass can be expressed in terms of energy and vice versa. If a particle has a frame of reference in which it lies at rest, then it has a positive rest mass and is referred to as massive.
All composite particles are massive. Baryons (meaning "heavy") tend to have greater mass than mesons (meaning "intermediate"), which in turn tend to be heavier than leptons (meaning "lightweight"), but the heaviest lepton (the tau particle) is heavier than the two lightest flavours of baryons (nucleons). It is also certain that any particle with an electric charge is massive.
Through the work of Albert Einstein, Satyendra Nath Bose, Louis de Broglie, and many others, current scientific theory holds that all particles also have a wave nature. This has been verified not only for elementary particles but also for compound particles like atoms and even molecules. In fact, according to traditional formulations of non-relativistic quantum mechanics, wave–particle duality applies to all objects, even macroscopic ones; although the wave properties of macroscopic objects cannot be detected due to their small wavelengths.
Interactions between particles have been scrutinized for many centuries, and a few simple laws underpin how particles behave in collisions and interactions. The most fundamental of these are the laws of conservation of energy and conservation of momentum, which let us make calculations of particle interactions on scales of magnitude that range from stars to quarks. These are the prerequisite basics of Newtonian mechanics, a series of statements and equations in Philosophiae Naturalis Principia Mathematica, originally published in 1687.
The negatively charged electron has a mass equal to 1⁄1837 or 1836 of that of a hydrogen atom. The remainder of the hydrogen atom's mass comes from the positively charged proton. The atomic number of an element is the number of protons in its nucleus. Neutrons are neutral particles having a mass slightly greater than that of the proton. Different isotopes of the same element contain the same number of protons but differing numbers of neutrons. The mass number of an isotope is the total number of nucleons (neutrons and protons collectively).
Chemistry concerns itself with how electron sharing binds atoms into structures such as crystals and molecules. Nuclear physics deals with how protons and neutrons arrange themselves in nuclei. The study of subatomic particles, atoms and molecules, and their structure and interactions, requires quantum mechanics. Analyzing processes that change the numbers and types of particles requires quantum field theory. The study of subatomic particles per se is called particle physics. The term high-energy physics is nearly synonymous to "particle physics" since creation of particles requires high energies: it occurs only as a result of cosmic rays, or in particle accelerators. Particle phenomenology systematizes the knowledge about subatomic particles obtained from these experiments.
The term "subatomic particle" is largely a retronym of the 1960s, used to distinguish a large number of baryons and mesons (which comprise hadrons) from particles that are now thought to be truly elementary. Before that hadrons were usually classified as "elementary" because their composition was unknown.
A list of important discoveries follows:
|elementary (lepton)||G. Johnstone Stoney (1874)||J. J. Thomson (1897)||Minimum unit of electrical charge, for which Stoney suggested the name in 1891.|
|composite (atomic nucleus)||never||Ernest Rutherford (1899)||Proven by Rutherford and Thomas Royds in 1907 to be helium nuclei.|
|elementary (quantum)||Max Planck (1900)||Albert Einstein (1905)
or Ernest Rutherford (1899) as γ rays
|Necessary to solve the problem of black-body radiation in thermodynamics.|
|composite (baryon)||Long ago||Ernest Rutherford (1919, named 1920)||The nucleus of 1|
|composite (baryon)||Ernest Rutherford (c.1918)||James Chadwick (1932)||The second nucleon.|
|Antiparticles||Paul Dirac (1928)||Carl D. Anderson (
|Now explained with CPT symmetry.|
|composite (mesons)||Hideki Yukawa (1935)||César Lattes, Giuseppe Occhialini (1947) and Cecil Powell||Explains the nuclear force between nucleons. The first meson (by modern definition) to be discovered.|
|elementary (lepton)||never||Carl D. Anderson (1936)||The first named meson; today considered a lepton.|
|composite (mesons)||never||1947||Discovered in cosmic rays. The first strange particle.|
|composite (baryons)||never||University of Melbourne (
|The first hyperon discovered.|
|elementary (lepton)||Wolfgang Pauli (1930), named by Enrico Fermi||Clyde Cowan, Frederick Reines (
|Solved the problem of energy spectrum of beta decay.|
|elementary||Murray Gell-Mann, George Zweig (1964)||No particular confirmation event for the quark model.|
|Weak gauge bosons||elementary (quantum)||Glashow, Weinberg, Salam (1968)||CERN (1983)||Properties verified through the 1990s.|
|elementary (quark)||1973||1995||Does not hadronize, but is necessary to complete the Standard Model.|
|Higgs boson||elementary (quantum)||Peter Higgs et al. (1964)||CERN (2012)||Thought to be confirmed in 2013. More evidence found in 2014.|
|Tetraquark||composite||?||Zc(3900), 2013, to be confirmed as a tetraquark||A new class of hadrons.|
|Graviton||elementary (quantum)||Albert Einstein (1916)||Not discovered||Interpretation of a gravitational wave as a particle is controversial.|
|Magnetic monopole||elementary (unclassified)||Paul Dirac (1931)||Not discovered|
For both large and small wavelengths, both matter and radiation have both particle and wave aspects. [...] But the wave aspects of their motion become more difficult to observe as their wavelengths become shorter. [...] For ordinary macroscopic particles the mass is so large that the momentum is always sufficiently large to make the de Broglie wavelength small enough to be beyond the range of experimental detection, and classical mechanics reigns supreme.
The Delta baryons (or Δ baryons, also called Delta resonances) are a family of subatomic particle made of three up or down quarks (u or d quarks).
Four closely related Δ baryons exist: Δ++ (constituent quarks: uuu), Δ+ (uud), Δ0 (udd), and Δ− (ddd), which respectively carry an electric charge of +2 e, +1 e, 0 e, and −1 e. The Δ baryons have a mass of about 1232 MeV/c2, a spin of 3⁄2, and an isospin of 3⁄2. Ordinary protons and neutrons (nucleons (symbol N)), by contrast, have a mass of about 939 MeV/c2, a spin of 1⁄2, and an isospin of 1⁄2. The Δ+ (uud) and Δ0 (udd) particles are the higher-mass excitations of the proton (N+, uud) and neutron (N0, udd), respectively. However, the Δ++ and Δ− have no direct nucleon analogues.
The states were established experimentally at the University of Chicago cyclotron and the Carnegie Institute of Technology synchro-cyclotron in the mid-1950s using accelerated positive pions on hydrogen targets. The existence of the Δ++, with its unusual +2 charge, was a crucial clue in the development of the quark model.
The Delta states discussed here are only the lowest-mass quantum excitations of the proton and neutron. At higher masses, additional Delta states appear, all defined by having 3⁄2 units of isospin, but with a spin quantum numbers including 1⁄2, 3⁄2, 5⁄2, ... 11⁄2. A complete listing of all properties of all these states can be found in Beringer et al (2013).There also exist antiparticle Delta states with opposite charges, made up of the corresponding antiquarks.Diquark
In particle physics, a diquark, or diquark correlation/clustering, is a hypothetical state of two quarks grouped inside a baryon (that consists of three quarks) (Lichtenberg 1982). Corresponding models of baryons are referred to as quark–diquark models. The diquark is often treated as a single subatomic particle with which the third quark interacts via the strong interaction. The existence of diquarks inside the nucleons is a disputed issue, but it helps to explain some nucleon properties and to reproduce experimental data sensitive to the nucleon structure. Diquark–antidiquark pairs have also been advanced for anomalous particles such as the X(3872).George Rochester
George Dixon Rochester, FRS (February 4, 1908 – December 26, 2001) was a British physicist known for having co-discovered, with Sir Clifford Charles Butler, a subatomic particle called the kaon.Born in Wallsend, North Tyneside in northern England, he received a Bachelor of Science degree, a Master of Science degree, and a Ph.D. from Armstrong College, Newcastle (then part of Durham University now Newcastle University). He did his postdoctoral research at the University of California, Berkeley and then joined the faculty of Manchester University eventually becoming a Reader in 1953. In 1955, he was appointed Professor of Physics and Chair of the Department at Durham University. He was elected a Fellow of the Royal Society in 1958. From 1967 to 1970, he was a Pro-Vice-Chancellor of the University. He retired in 1973.
The Durham Physics Department has hosted the annual Rochester Lecture since 1975. In 1997, on the 50th anniversary of the discover of the kaon, the physics building in Durham (which he had been involved in designing) was named the Rochester Building in his honour.Hadron
In particle physics, a hadron (listen) (Greek: ἁδρός, hadrós; "stout, thick") is a composite particle made of two or more quarks held together by the strong force in a similar way as molecules are held together by the electromagnetic force. Most of the mass of ordinary matter comes from two hadrons, the proton and the neutron.
Hadrons are categorized into two families: baryons, made of an odd number of quarks – usually three quarks – and mesons, made of an even number of quarks—usually one quark and one antiquark. Protons and neutrons are examples of baryons; pions are an example of a meson. "Exotic" hadrons, containing more than three valence quarks, have been discovered in recent years. A tetraquark state (an exotic meson), named the Z(4430)−, was discovered in 2007 by the Belle Collaboration and confirmed as a resonance in 2014 by the LHCb collaboration. Two pentaquark states (exotic baryons), named P+c(4380) and P+c(4450), were discovered in 2015 by the LHCb collaboration. There are several more exotic hadron candidates, and other colour-singlet quark combinations that may also exist.
Almost all "free" hadrons and antihadrons (meaning, in isolation and not bound within an atomic nucleus) are believed to be unstable and eventually decay (break down) into other particles. The only known exception relates to free protons, which are possibly stable, or at least, take immense amounts of time to decay (order of 1034+ years). Free neutrons are unstable and decay with a half-life of about 611 seconds. Their respective antiparticles are expected to follow the same pattern, but they are difficult to capture and study, because they immediately annihilate on contact with ordinary matter. "Bound" protons and neutrons, contained within an atomic nucleus, are generally considered stable. Experimentally, hadron physics is studied by colliding protons or nuclei of heavy elements such as lead or gold, and detecting the debris in the produced particle showers. In the environment, mesons such as pions are produced by the collisions of cosmic rays with the atmosphere.Minicharged particle
Minicharged particles (or milli-charged particles) are a proposed type of subatomic particle. They are charged, but with a tiny fraction of the charge of the electron. They weakly interact with matter. Minicharged particles are not part of the Standard Model. One proposal to detect them involved photons tunneling through an opaque barrier in the presence of a perpendicular magnetic field, the rationale being that a pair of oppositely charged minicharged particles are produced that curve in opposite directions, and recombine on the other side of the barrier reproducing the photon again.Minicharged particles would result in vacuum magnetic dichroism, and would cause energy loss in microwave cavities. Photons from the cosmic microwave background would be dissipated by galactic-scale magnetic fields if minicharged particles existed, so this effect could be observable. In fact the dimming observed of remote supernovae that was used to support dark energy could also be explained by the formation of minicharged particles.Tests of Coulomb's law can be applied to set bounds on minicharged particles.Muon neutrino
The muon neutrino is a lepton, an elementary subatomic particle which has the symbol νμ and no net electric charge. Together with the muon it forms the second generation of leptons, hence the name muon neutrino. It was first hypothesized in the early 1940s by several people, and was discovered in 1962 by Leon Lederman, Melvin Schwartz and Jack Steinberger. The discovery was rewarded with the 1988 Nobel Prize in Physics.Neuter
Neuter is a Latin adjective meaning "neither", and can refer to:
Neuter gender, a grammatical gender, a linguistic class of nouns triggering specific types of inflections in associated words
Neutering, the sterilization of an animalNeutron (disambiguation)
Neutron is a subatomic particle.
Neutron may also refer to:
Neutron (bot), an XMPP bot written in Python using xmpppy library
Neutron (game), an abstract strategy game
Neutron (formerly Quantum), a software system for managing virtualized network topologies in the OpenStack cloud computing platformPair production
Pair production is the creation of a subatomic particle and its antiparticle from a neutral boson. Examples include creating an electron and a positron, a muon and an antimuon, or a proton and an antiproton. Pair production often refers specifically to a photon creating an electron-positron pair near a nucleus. For pair production to occur, the incoming energy of the interaction must be above a threshold of at least the total rest mass energy of the two particles, and the situation must conserve both energy and momentum. However, all other conserved quantum numbers (angular momentum, electric charge, lepton number) of the produced particles must sum to zero – thus the created particles shall have opposite values of each other. For instance, if one particle has electric charge of +1 the other must have electric charge of −1, or if one particle has strangeness of +1 then another one must have strangeness of −1.
The probability of pair production in photon-matter interactions increases with photon energy and also increases approximately as the square of atomic number of the nearby atom.Particle decay
Particle decay is the spontaneous process of one unstable subatomic particle transforming into multiple other particles. The particles created in this process (the final state) must each be less massive than the original, although the total invariant mass of the system must be conserved. A particle is unstable if there is at least one allowed final state that it can decay into. Unstable particles will often have multiple ways of decaying, each with its own associated probability. Decays are mediated by one or several fundamental forces. The particles in the final state may themselves be unstable and subject to further decay.
The term is typically distinct from radioactive decay, in which an unstable atomic nucleus is transformed into a lighter nucleus accompanied by the emission of particles or radiation, although the two are conceptually similar and are often described using the same terminology.Photino
A photino is a hypothetical subatomic particle, the fermion WIMP superpartner of the photon predicted by supersymmetry. It is an example of a gaugino. Even though no photino has ever been observed so far, it is one of the candidates for the lightest stable particle in the universe. It is proposed that photinos are produced by sources of ultra-high-energy cosmic rays.Photodisintegration
Photodisintegration (also called phototransmutation) is a nuclear process in which an atomic nucleus absorbs a high-energy gamma ray, enters an excited state, and immediately decays by emitting a subatomic particle. The incoming gamma ray effectively knocks one or more neutrons, protons, or an alpha particle out of the nucleus. The reactions are called (γ,n), (γ,p), and (γ,α).
Photodisintegration is endothermic (energy absorbing) for atomic nuclei lighter than iron and sometimes exothermic (energy releasing) for atomic nuclei heavier than iron. Photodisintegration is responsible for the nucleosynthesis of at least some heavy, proton-rich elements via the p-process in supernovae.Scientific glassblowing
Scientific glassblowing is a specialty field of glass blowing used in industry, science, art and design used in research and production. Scientific glassblowing has been used in chemical, pharmaceutical, electronic and physics research including Galileo’s thermometer, Thomas Edison’s light bulb, and vacuum tubes used in early radio, TV and computers. More recently, the field has helped advance fiber optics, lasers, atomic and subatomic particle research, advanced communications development and semiconductors. The field combined hand skills using lathes and torches with modern computer assisted furnaces, diamond grinding and lapping machines, lasers and ultra-sonic mills.The Book of Dust
The Book of Dust is an as-yet-uncompleted trilogy of fantasy novels by Philip Pullman, which expands Pullman's His Dark Materials trilogy. The epic further chronicles the adventures of Lyra Belacqua and her battle against the theocratic organisation known as the Magisterium, as well as shedding more light on a mysterious substance called Dust.
The first book, La Belle Sauvage, was published in October 2017, and is set 12 years before Northern Lights, the first book of the original trilogy. It describes the 11-year-old protagonist Malcolm Polstead's efforts, with a girl named Alice, to protect the baby Lyra, the events which left Lyra in the care of Jordan College, the early research by academics and other free-thinkers into Dust, a mysterious subatomic particle related to consciousness, and the origins of Lyra's "alethiometer". The second and third books, as yet unpublished, are described as being set after the events in the original trilogy.
Pullman said the trilogy addresses consciousness: "Perhaps the oldest philosophical question of all: are we matter? Or are we spirit and matter? What is consciousness if there is no spirit? Questions like that are of perennial fascination and they haven’t been solved yet, thank goodness.” He added that the series might be slightly darker than the original, and quipped that it alternatively be titled "His Darker Materials".Top quark
The top quark, also known as the t quark (symbol: t) or truth quark, is the most massive of all observed elementary particles. Like all quarks, the top quark is a fermion with spin 1/2, and experiences all four fundamental interactions: gravitation, electromagnetism, weak interactions, and strong interactions. It has an electric charge of +2/3 e. It has a mass of 173.0 ± 0.4 GeV/c2, which is about the same mass as an atom of rhenium. The antiparticle of the top quark is the top antiquark (symbol: t, sometimes called antitop quark or simply antitop), which differs from it only in that some of its properties have equal magnitude but opposite sign.
The top quark interacts primarily by the strong interaction, but can only decay through the weak force. It decays to a W boson and either a bottom quark (most frequently), a strange quark, or, on the rarest of occasions, a down quark. The Standard Model predicts its mean lifetime to be roughly 5×10−25 s. This is about a twentieth of the timescale for strong interactions, and therefore it does not form hadrons, giving physicists a unique opportunity to study a "bare" quark (all other quarks hadronize, meaning that they combine with other quarks to form hadrons, and can only be observed as such). Because it is so massive, the properties of the top quark allow predictions to be made of the mass of the Higgs boson under certain extensions of the Standard Model (see Mass and coupling to the Higgs boson below). As such, it is extensively studied as a means to discriminate between competing theories.
Its existence (and that of the bottom quark) was postulated in 1973 by Makoto Kobayashi and Toshihide Maskawa to explain the observed CP violations in kaon decay, and was discovered in 1995 by the CDF and DØ experiments at Fermilab. Kobayashi and Maskawa won the 2008 Nobel Prize in Physics for the prediction of the top and bottom quark, which together form the third generation of quarks.Truly neutral particle
In particle physics, a truly neutral particle is a subatomic particle with all its charges equal to zero. This not only requires particles to be electrically neutral, but also requires that all of their other charges (like the colour charge) are neutral. Such a particle will be its own antiparticle.
Mathematically, charge conjugation replaces all the constituent particles of a particle with their corresponding antiparticles. If a particle remains the same after charge conjugation, then it is its own antiparticle, and is truly neutral.
Known examples of such elementary particles include photons, Z bosons, and Higgs bosons, along with the hypothetical neutralinos, sterile neutrinos, and gravitons. For a spin-1/2 particle such as the neutralino, being a truly neutral particle implies being a Majorana fermion.
Composite particles can also be truly neutral. The best known example is onium, a system composed of a particle forming a bound state with its own antiparticle.Zc(3900)
The Zc(3900) is a hadron, a type of subatomic particle made of quarks, believed to be the first tetraquark that has been observed experimentally. The discovery was made in 2013 by two independent research groups: one using the BES III detector at the Chinese Beijing Electron Positron Collider, the other being part of the Belle experiment group at the Japanese KEK particle physics laboratory.The Zc(3900) is a decay product of the previously observed anomalous Y(4260) particle.The Zc(3900) in turn decays into a charged pion (π±) and a J/ψ meson. This is consistent with the Zc(3900) containing four or more quarks.The first evidence of the neutral Zc(3900) was provided by CLEO-c in 2013. It was later observed by BESIII in 2015. It decays into a neutral pion (π0) and a J/ψ meson.Researchers were expected to run decay experiments in 2013 to determine the particle's nature with more precision.