Timeline of particle discoveries

This is a timeline of subatomic particle discoveries, including all particles thus far discovered which appear to be elementary (that is, indivisible) given the best available evidence. It also includes the discovery of composite particles and antiparticles that were of particular historical importance.

More specifically, the inclusion criteria are:

  • Elementary particles from the Standard Model of particle physics that have so far been observed. The Standard Model is the most comprehensive existing model of particle behavior. All Standard Model particles including the Higgs boson have been verified, and all other observed particles are combinations of two or more Standard Model particles.
  • Antiparticles which were historically important to the development of particle physics, specifically the positron and antiproton. The discovery of these particles required very different experimental methods from that of their ordinary matter counterparts, and provided evidence that all particles had antiparticles—an idea that is fundamental to quantum field theory, the modern mathematical framework for particle physics. In the case of most subsequent particle discoveries, the particle and its anti-particle were discovered essentially simultaneously.
  • Composite particles which were the first particle discovered containing a particular elementary constituent, or whose discovery was critical to the understanding of particle physics.
Time Event
1800 William Herschel discovers "heat rays"
1801 Johann Wilhelm Ritter made the hallmark observation that invisible rays just beyond the violet end of the visible spectrum were especially effective at lightening silver chloride-soaked paper. He called them "oxidizing rays" to emphasize chemical reactivity and to distinguish them from "heat rays" at the other end of the invisible spectrum (both of which were later determined to be photons). The more general term "chemical rays" was adopted shortly thereafter to describe the oxidizing rays, and it remained popular throughout the 19th century. The terms chemical and heat rays were eventually dropped in favor of ultraviolet and infrared radiation, respectively.[1]
1895 Discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet (later identified as photons) because it is strongly absorbed by air, by the German physicist Victor Schumann[2]
1895 X-ray produced by Wilhelm Röntgen (later identified as photons)[3]
1897 Electron discovered by J. J. Thomson[4]
1899 Alpha particle discovered by Ernest Rutherford in uranium radiation[5]
1900 Gamma ray (a high-energy photon) discovered by Paul Villard in uranium decay[6]
1911 Atomic nucleus identified by Ernest Rutherford, based on scattering observed by Hans Geiger and Ernest Marsden[7]
1919 Proton discovered by Ernest Rutherford[8]
1931 Deuteron discovered by Harold Urey[9][10] (predicted by Rutherford in 1920[11])
1932 Neutron discovered by James Chadwick[12] (predicted by Rutherford in 1920[11])
1932 Antielectron (or positron), the first antiparticle, discovered by Carl D. Anderson[13] (proposed by Paul Dirac in 1927 and by Ettore Majorana in 1928)
1937 Muon (or mu lepton) discovered by Seth Neddermeyer, Carl D. Anderson, J.C. Street, and E.C. Stevenson, using cloud chamber measurements of cosmic rays[14] (it was mistaken for the pion until 1947[15])
1947 Pion (or pi meson) discovered by C. F. Powell's group, including César Lattes(first author) and Giuseppe Occhialini (predicted by Hideki Yukawa in 1935[16])
1947 Kaon (or K meson), the first strange particle, discovered by George Dixon Rochester and Clifford Charles Butler[17]
(or lambda baryon) discovered during a study of cosmic-ray interactions[18]
1955 Antiproton discovered by Owen Chamberlain, Emilio Segrè, Clyde Wiegand, and Thomas Ypsilantis[19]
1956 Electron neutrino detected by Frederick Reines and Clyde Cowan (proposed by Wolfgang Pauli in 1930 to explain the apparent violation of conservation of energy in beta decay)[20] At the time it was simply referred to as neutrino since there was only one known neutrino.
1962 Muon neutrino (or mu neutrino) shown to be distinct from the electron neutrino by a group headed by Leon Lederman[21]
1964 Xi baryon discovery at Brookhaven National Laboratory[22]
1969 Partons (internal constituents of hadrons) observed in deep inelastic scattering experiments between protons and electrons at SLAC;[23][24] this was eventually associated with the quark model (predicted by Murray Gell-Mann and George Zweig in 1964) and thus constitutes the discovery of the up quark, down quark, and strange quark.
1974 J/ψ meson discovered by groups headed by Burton Richter and Samuel Ting, demonstrating the existence of the charm quark[25][26] (proposed by James Bjorken and Sheldon Lee Glashow in 1964[27])
1975 Tau discovered by a group headed by Martin Perl[28]
1977 Upsilon meson discovered at Fermilab, demonstrating the existence of the bottom quark[29] (proposed by Kobayashi and Maskawa in 1973)
1979 Gluon observed indirectly in three-jet events at DESY[30]
1983 W and Z bosons discovered by Carlo Rubbia, Simon van der Meer, and the CERN UA1 collaboration[31][32] (predicted in detail by Sheldon Glashow, Mohammad Abdus Salam, and Steven Weinberg)
1995 Top quark discovered at Fermilab[33][34]
1995 Antihydrogen produced and measured by the LEAR experiment at CERN[35]
2000 Tau neutrino first observed directly at Fermilab[36]
2011 Antihelium-4 produced and measured by the STAR detector; the first particle to be discovered by the experiment
2012 A particle exhibiting most of the predicted characteristics of the Higgs boson discovered by researchers conducting the Compact Muon Solenoid and ATLAS experiments at CERN's Large Hadron Collider[37]

See also


  1. ^ Hockberger, P. E. (2002). "A history of ultraviolet photobiology for humans, animals and microorganisms". Photochem. Photobiol. 76 (6): 561–579. doi:10.1562/0031-8655(2002)0760561AHOUPF2.0.CO2. ISSN 0031-8655. PMID 12511035.
  2. ^ The ozone layer protects humans from this. Lyman, T. (1914). "Victor Schumann". Astrophysical Journal. 38: 1–4. Bibcode:1914ApJ....39....1L. doi:10.1086/142050.
  3. ^ W.C. Röntgen (1895). "Über ein neue Art von Strahlen. Vorlaufige Mitteilung". Sitzber. Physik. Med. Ges. 137: 1. as translated in A. Stanton (1896). "On a New Kind of Rays". Nature. 53 (1369): 274–276. Bibcode:1896Natur..53R.274.. doi:10.1038/053274b0.
  4. ^ J.J. Thomson (1897). "Cathode Rays". Philosophical Magazine. 44 (269): 293–316. doi:10.1080/14786449708621070.
  5. ^ E. Rutherford (1899). "Uranium Radiation and the Electrical Conduction Produced by it". Philosophical Magazine. 47 (284): 109–163. doi:10.1080/14786449908621245.
  6. ^ P. Villard (1900). "Sur la Réflexion et la Réfraction des Rayons Cathodiques et des Rayons Déviables du Radium". Comptes Rendus de l'Académie des Sciences. 130: 1010.
  7. ^ E. Rutherford (1911). "The Scattering of α- and β- Particles by Matter and the Structure of the Atom". Philosophical Magazine. 21 (125): 669–688. doi:10.1080/14786440508637080.
  8. ^ E. Rutherford (1919). "Collision of α Particles with Light Atoms IV. An Anomalous Effect in Nitrogen". Philosophical Magazine. 37: 581.
  9. ^ Brickwedde, Ferdinand G. (1982). "Harold Urey and the discovery of deuterium". Physics Today. 35 (9): 34. Bibcode:1982PhT....35i..34B. doi:10.1063/1.2915259.
  10. ^ Urey, Harold; Brickwedde, F.; Murphy, G. (1932). "A Hydrogen Isotope of Mass 2". Physical Review. 39 (1): 164–165. Bibcode:1932PhRv...39..164U. doi:10.1103/PhysRev.39.164.
  11. ^ a b E. Rutherford (1920). "Nuclear Constitution of Atoms". Proceedings of the Royal Society A. 97 (686): 374–400. Bibcode:1920RSPSA..97..374R. doi:10.1098/rspa.1920.0040.
  12. ^ J. Chadwick (1932). "Possible Existence of a Neutron". Nature. 129 (3252): 312. Bibcode:1932Natur.129Q.312C. doi:10.1038/129312a0.
  13. ^ C.D. Anderson (1932). "The Apparent Existence of Easily Deflectable Positives". Science. 76 (1967): 238–9. Bibcode:1932Sci....76..238A. doi:10.1126/science.76.1967.238. PMID 17731542.
  14. ^ S.H. Neddermeyer; C.D. Anderson (1937). "Note on the nature of Cosmic-Ray Particles". Physical Review. 51 (10): 884–886. Bibcode:1937PhRv...51..884N. doi:10.1103/PhysRev.51.884.
  15. ^ M. Conversi; E. Pancini; O. Piccioni (1947). "On the Disintegration of Negative Muons". Physical Review. 71 (3): 209–210. Bibcode:1947PhRv...71..209C. doi:10.1103/PhysRev.71.209.
  16. ^ H. Yukawa (1935). "On the Interaction of Elementary Particles". Proceedings of the Physico-Mathematical Society of Japan. 17: 48.
  17. ^ G.D. Rochester; C.C. Butler (1947). "Evidence for the Existence of New Unstable Elementary Particles". Nature. 160 (4077): 855–857. Bibcode:1947Natur.160..855R. doi:10.1038/160855a0.
  18. ^ The Strange Quark
  19. ^ O. Chamberlain; E. Segrè; C. Wiegand; T. Ypsilantis (1955). "Observation of Antiprotons". Physical Review. 100 (3): 947–950. Bibcode:1955PhRv..100..947C. doi:10.1103/PhysRev.100.947.
  20. ^ F. Reines; C.L. Cowan (1956). "The Neutrino". Nature. 178 (4531): 446–449. Bibcode:1956Natur.178..446R. doi:10.1038/178446a0.
  21. ^ G. Danby; et al. (1962). "Observation of High-Energy Neutrino Reactions and the Existence of Two Kinds of Neutrinos". Physical Review Letters. 9 (1): 36–44. Bibcode:1962PhRvL...9...36D. doi:10.1103/PhysRevLett.9.36.
  22. ^ R. Nave. "The Xi Baryon". Hyperphysics. Retrieved 20 June 2009.
  23. ^ E.D. Bloom; et al. (1969). "High-Energy Inelastic ep Scattering at 6° and 10°". Physical Review Letters. 23 (16): 930–934. Bibcode:1969PhRvL..23..930B. doi:10.1103/PhysRevLett.23.930.
  24. ^ M. Breidenbach; et al. (1969). "Observed Behavior of Highly Inelastic Electron-Proton Scattering". Physical Review Letters. 23 (16): 935–939. Bibcode:1969PhRvL..23..935B. doi:10.1103/PhysRevLett.23.935.
  25. ^ J.J. Aubert; et al. (1974). "Experimental Observation of a Heavy Particle J". Physical Review Letters. 33 (23): 1404–1406. Bibcode:1974PhRvL..33.1404A. doi:10.1103/PhysRevLett.33.1404.
  26. ^ J.-E. Augustin; et al. (1974). "Discovery of a Narrow Resonance in e+e Annihilation". Physical Review Letters. 33 (23): 1406–1408. Bibcode:1974PhRvL..33.1406A. doi:10.1103/PhysRevLett.33.1406.
  27. ^ B.J. Bjørken; S.L. Glashow (1964). "Elementary Particles and SU(4)". Physics Letters. 11 (3): 255–257. Bibcode:1964PhL....11..255B. doi:10.1016/0031-9163(64)90433-0.
  28. ^ M.L. Perl; et al. (1975). "Evidence for Anomalous Lepton Production in e+e Annihilation". Physical Review Letters. 35 (22): 1489–1492. Bibcode:1975PhRvL..35.1489P. doi:10.1103/PhysRevLett.35.1489.
  29. ^ S.W. Herb; et al. (1977). "Observation of a Dimuon Resonance at 9.5 GeV in 400-GeV Proton-Nucleus Collisions". Physical Review Letters. 39 (5): 252–255. Bibcode:1977PhRvL..39..252H. doi:10.1103/PhysRevLett.39.252.
  30. ^ D.P. Barber; et al. (1979). "Discovery of Three-Jet Events and a Test of Quantum Chromodynamics at PETRA". Physical Review Letters. 43 (12): 830–833. Bibcode:1979PhRvL..43..830B. doi:10.1103/PhysRevLett.43.830.
  31. ^ J.J. Aubert et al. (European Muon Collaboration) (1983). "The ratio of the nucleon structure functions F2N for iron and deuterium". Physics Letters B. 123 (3–4): 275–278. Bibcode:1983PhLB..123..275A. doi:10.1016/0370-2693(83)90437-9.
  32. ^ G. Arnison et al. (UA1 collaboration) (1983). "Experimental observation of lepton pairs of invariant mass around 95 GeV/c2 at the CERN SPS collider". Physics Letters B. 126 (5): 398–410. Bibcode:1983PhLB..126..398A. doi:10.1016/0370-2693(83)90188-0.
  33. ^ F. Abe et al. (CDF collaboration) (1995). "Observation of Top quark production in p–p Collisions with the Collider Detector at Fermilab". Physical Review Letters. 74 (14): 2626–2631. arXiv:hep-ex/9503002. Bibcode:1995PhRvL..74.2626A. doi:10.1103/PhysRevLett.74.2626. PMID 10057978.
  34. ^ S. Arabuchi et al. (D0 collaboration) (1995). "Observation of the Top Quark". Physical Review Letters. 74 (14): 2632–2637. arXiv:hep-ex/9503003. Bibcode:1995PhRvL..74.2632A. doi:10.1103/PhysRevLett.74.2632. PMID 10057979.
  35. ^ G. Baur; et al. (1996). "Production of Antihydrogen". Physics Letters B. 368 (3): 251–258. Bibcode:1996PhLB..368..251B. CiteSeerX doi:10.1016/0370-2693(96)00005-6.
  36. ^ "Physicists Find First Direct Evidence for Tau Neutrino at Fermilab" (Press release). Fermilab. 20 July 2000. Retrieved 20 March 2010.
  37. ^ Boyle, Alan (4 July 2012). "Milestone in Higgs quest: Scientists find new particle". MSNBC. MSNBC. Retrieved 5 July 2012.
  • V.V. Ezhela; et al. (1996). Particle Physics: One Hundred Years of Discoveries: An Annotated Chronological Bibliography. Springer-Verlag. ISBN 978-1-56396-642-2.

In particle physics, a baryon is a type of composite subatomic particle which contains an odd number of valence quarks (at least 3). Baryons belong to the hadron family of particles, which are the quark-based particles. They are also classified as fermions, i.e., they have half-integer spin.

The name "baryon", introduced by Abraham Pais, comes from the Greek word for "heavy" (βαρύς, barýs), because, at the time of their naming, most known elementary particles had lower masses than the baryons. Each baryon has a corresponding antiparticle (antibaryon) where their corresponding antiquarks replace quarks. For example, a proton is made of two up quarks and one down quark; and its corresponding antiparticle, the antiproton, is made of two up antiquarks and one down antiquark.

As quark-based particles, baryons participate in the strong interaction, which is mediated by particles known as gluons. The most familiar baryons are protons and neutrons, both of which contain three quarks, and for this reason these particles are sometimes described as triquarks. These particles make up most of the mass of the visible matter in the universe, as well as forming the components of the nucleus of every atom. Electrons (the other major component of the atom) are members of a different family of particles, known as leptons, which do not interact via the strong force. Exotic baryons containing five quarks (known as pentaquarks) have also been discovered and studied.

D meson

The D mesons are the lightest particle containing charm quarks. They are often studied to gain knowledge on the weak interaction. The strange D mesons (Ds) were called the "F mesons" prior to 1986.

Experimental physics

Experimental physics is the category of disciplines and sub-disciplines in the field of physics that are concerned with the observation of physical phenomena and experiments. Methods vary from discipline to discipline, from simple experiments and observations, such as the Cavendish experiment, to more complicated ones, such as the Large Hadron Collider.

Gauge boson

In particle physics, a gauge boson is a force carrier, a bosonic particle that carries any of the fundamental interactions of nature, commonly called forces. Elementary particles, whose interactions are described by a gauge theory, interact with each other by the exchange of gauge bosons—usually as virtual particles.

All known gauge bosons have a spin of 1. Therefore, all known gauge bosons are vector bosons.

Gauge bosons are different from the other kinds of bosons: first, fundamental scalar bosons (the Higgs boson); second, mesons, which are composite bosons, made of quarks; third, larger composite, non-force-carrying bosons, such as certain atoms.


In particle physics, a hyperon is any baryon containing one or more strange quarks, but no charm, bottom, or top quark. This form of matter may exist in a stable form within the core of some neutron stars.

Index of physics articles (T)

The index of physics articles is split into multiple pages due to its size.

To navigate by individual letter use the table of contents below.

Intersecting Storage Rings

The ISR (standing for "Intersecting Storage Rings") was a particle accelerator at CERN. It was the world's first hadron collider, and ran from 1971 to 1984, with a maximum center of mass energy of 62 GeV. From its initial startup, the collider itself had the capability to produce particles like the J/ψ and the upsilon, as well as observable jet structure; however, the particle detector experiments were not configured to observe events with large momentum transverse to the beamline, leaving these discoveries to be made at other experiments in the mid-1970s. Nevertheless, the construction of the ISR involved many advances in accelerator physics, including the first use of stochastic cooling, and it held the record for luminosity at a hadron collider until surpassed by the Tevatron in 2004.

Johann Wilhelm Ritter

Johann Wilhelm Ritter (16 December 1776 – 23 January 1810) was a German chemist, physicist and philosopher. He was born in Samitz (Zamienice) near Haynau (Chojnów) in Silesia (then part of Prussia, since 1945 in Poland), and died in Munich.

List of baryons

Baryons are composite particles made of three quarks, as opposed to mesons, which are composite particles made of one quark and one antiquark. Baryons and mesons are both hadrons, which are particles composed solely of quarks or both quarks and antiquarks. The term baryon is derived from the Greek "βαρύς" (barys), meaning "heavy", because, at the time of their naming, it was believed that baryons were characterized by having greater masses than other particles that were classed as matter.

Until a few years ago, it was believed that some experiments showed the existence of pentaquarks – baryons made of four quarks and one antiquark. The particle physics community as a whole did not view their existence as likely by 2006. On 13 July 2015, the LHCb collaboration at CERN reported results consistent with pentaquark states in the decay of bottom Lambda baryons (Λ0b).Since baryons are composed of quarks, they participate in the strong interaction. Leptons, on the other hand, are not composed of quarks and as such do not participate in the strong interaction. The most famous baryons are the protons and neutrons that make up most of the mass of the visible matter in the universe, whereas electrons, the other major component of atoms, are leptons. Each baryon has a corresponding antiparticle known as an antibaryon in which quarks are replaced by their corresponding antiquarks. For example, a proton is made of two up quarks and one down quark, while its corresponding antiparticle, the antiproton, is made of two up antiquarks and one down antiquark.

List of mesons

This list is of all known and predicted scalar, pseudoscalar and vector mesons. See list of particles for a more detailed list of particles found in particle physics.This article contains a list of mesons, unstable subatomic particles composed of one quark and one antiquark. They are part of the hadron particle family – particles made of quarks. The other members of the hadron family are the baryons – subatomic particles composed of three quarks. The main difference between mesons and baryons is that mesons have integer spin (thus are bosons) while baryons are fermions (half-integer spin). Because mesons are bosons, the Pauli exclusion principle does not apply to them. Because of this, they can act as force mediating particles on short distances, and thus play a part in processes such as the nuclear interaction.

Since mesons are composed of quarks, they participate in both the weak and strong interactions. Mesons with net electric charge also participate in the electromagnetic interaction. They are classified according to their quark content, total angular momentum, parity, and various other properties such as C-parity and G-parity. While no meson is stable, those of lower mass are nonetheless more stable than the most massive mesons, and are easier to observe and study in particle accelerators or in cosmic ray experiments. They are also typically less massive than baryons, meaning that they are more easily produced in experiments, and will exhibit higher-energy phenomena sooner than baryons would. For example, the charm quark was first seen in the J/Psi meson (J/ψ) in 1974, and the bottom quark in the upsilon meson (ϒ) in 1977.Each meson has a corresponding antiparticle (antimeson) where quarks are replaced by their corresponding antiquarks and vice versa. For example, a positive pion (π+) is made of one up quark and one down antiquark; and its corresponding antiparticle, the negative pion (π−), is made of one up antiquark and one down quark. Some experiments show the evidence of tetraquarks – "exotic" mesons made of two quarks and two antiquarks, but the particle physics community as a whole does not view their existence as likely, although still possible.The symbols encountered in these lists are: I (isospin), J (total angular momentum), P (parity), C (C-parity), G (G-parity), u (up quark), d (down quark), s (strange quark), c (charm quark), b (bottom quark), Q (charge), B (baryon number), S (strangeness), C (charm), and B′ (bottomness), as well as a wide array of subatomic particles (hover for name).

List of particles

This article includes a list of the different types of atomic and sub-atomic particles found or hypothesized to exist in the whole of the universe, categorized by type. Properties of the various particles listed are also given, as well as the laws that the particles follow. For individual lists of the different particles, see the list below.

List of timelines

This is a list of timelines currently on Wikipedia.

Omega baryon

The omega baryons are a family of subatomic hadron (a baryon) particles that are represented by the symbol Ω and are either neutral or have a +2, +1 or −1 elementary charge. They are baryons containing no up or down quarks. Omega baryons containing top quarks are not expected to be observed. This is because the Standard Model predicts the mean lifetime of top quarks to be roughly 5×10−25 s, which is about a twentieth of the timescale for strong interactions, and therefore that they do not form hadrons.

The first omega baryon discovered was the Ω−, made of three strange quarks, in 1964. The discovery was a great triumph in the study of quark processes, since it was found only after its existence, mass, and decay products had been predicted in 1961 by the American physicist Murray Gell-Mann and, independently, by the Israeli physicist Yuval Ne'eman. Besides the Ω−, a charmed omega particle (Ω0c) was discovered, in which a strange quark is replaced by a charm quark. The Ω− decays only via the weak interaction and has therefore a relatively long lifetime. Spin (J) and parity (P) values for unobserved baryons are predicted by the quark model.Since omega baryons do not have any up or down quarks, they all have isospin 0.

Sigma baryon

The Sigma baryons are a family of subatomic hadron particles which have two quarks from the first flavour generation (up and/or down quarks), and a third quark from higher flavour generations, in a combination where the wavefunction does not swap sign when any two quark flavours are swapped. They are thus baryons, with total Isospin of 1, and can either be neutral or have an elementary charge of +2, +1, 0, or −1. They are closely related to the Lambda baryons, which differ only in the wavefunction's behaviour upon flavour exchange.

The third quark can hence be either a strange (symbols Σ+, Σ0, Σ−), a charm (symbols Σ++c, Σ+c, Σ0c), a bottom (symbols Σ+b, Σ0b, Σ−b) or a top (symbols Σ++t, Σ+t, Σ0t) quark. However, the top Sigmas are not expected to be observed as the Standard Model predicts the mean lifetime of top quarks to be roughly 5×10−25 s. This is about 20 times shorter than the timescale for strong interactions, and therefore it does not form hadrons.

Xi baryon

The Xi baryons or cascade particles are a family of subatomic hadron particles which have the symbol Ξ and may have an electric charge (Q) of +2 e, +1 e, 0, or −1 e, where e is the elementary charge. Like all conventional baryons, they contain three quarks. Xi baryons, in particular, contain one up or down quark plus two more massive quarks: either strange, charm or bottom. They are historically called the cascade particles because of their unstable state; they decay rapidly into lighter particles through a chain of decays. The first discovery of a charged Xi baryon was in cosmic ray experiments by the Manchester group in 1952. The first discovery of the neutral Xi particle was at Lawrence Berkeley Laboratory in 1959. It was also observed as a daughter product from the decay of the omega baryon (Ω−) observed at Brookhaven National Laboratory in 1964. The Xi spectrum is important to nonperturbative quantum chromodynamics (QCD), such as Lattice QCD.

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