Inphysics,asubatomic particleis aparticlesmaller than anatom.[1]According to theStandard Model of particle physics,a subatomic particle can be either acomposite particle,which is composed of other particles (for example, abaryon,like aprotonor aneutron,composed of threequarks;or ameson,composed of twoquarks), or anelementary particle,which is not composed of other particles (for example, quarks; orelectrons,muons,andtauparticles, which are calledleptons).[2]Particle physicsandnuclear physicsstudy these particles and how they interact.[3]Most force-carrying particles likephotonsorgluonsare calledbosonsand, although they have quanta of energy, do not have rest mass or discrete diameters (other than pure energy wavelength) and are unlike the former particles that have rest mass and cannot overlap or combine which are calledfermions.TheW and Z bosons,however, are an exception to this rule and have relatively large rest masses at approximately 80GeVand 90 GeV respectively.
Experiments show that light could behave like astream of particles(calledphotons) as well as exhibiting wave-like properties. This led to the concept ofwave–particle dualityto reflect that quantum-scaleparticlesbehave both like particles and likewaves;they are sometimes calledwaviclesto reflect this.[4]
Another concept, theuncertainty principle,states that some of their properties taken together, such as their simultaneouspositionandmomentum,cannot be measured exactly.[5]The wave–particle duality has been shown to apply not only to photons but to more massive particles as well.[6]
Interactions of particles in the framework ofquantum field theoryare understood as creation and annihilation ofquantaof correspondingfundamental interactions.This blends particle physics withfield theory.
Even amongparticle physicists,the exact definition of a particle has diverse descriptions. These professional attempts at the definition of a particle include:[7]
- A particle is acollapsed wave function
- A particle is aquantum excitation of a field
- A particle is anirreducible representation of the Poincaré group
- A particle is an observed thing
| Subatomic particle | Symbol | Type | Location in atom | Charge (e) |
Mass (Da) |
|---|---|---|---|---|---|
| Proton | p+ | Composite | Nucleus | +1 | ≈ 1 |
| Neutron | n0 | Composite | Nucleus | 0 | ≈ 1 |
| Electron | e− | Elementary | Shells | −1 | ≈1/2000 |
Classification
editBy composition
editSubatomic particles are either "elementary", i.e. not made of multiple other particles, or "composite" and made of more than one elementary particle bound together.
The elementary particles of theStandard Modelare:[8]
- Six "flavors"ofquarks:up,down,strange,charm,bottom,andtop;
- Six types ofleptons:electron,electron neutrino,muon,muon neutrino,tau,tau neutrino;
- Twelvegauge bosons(force carriers): the photon ofelectromagnetism,the three W and Z bosons of theweak force,and the eight gluons of thestrong force;
- TheHiggs boson.
All of these have now been discovered through experiments, with the latest being the top quark (1995), tau neutrino (2000), and Higgs boson (2012).
Variousextensions of the Standard Modelpredict the existence of an elementarygravitonparticle andmany other elementary particles,but none have been discovered as of 2021.
Hadrons
editThe word hadron comes from Greek and was introduced in 1962 byLev Okun.[9]Nearly all composite particles contain multiple quarks (and/or antiquarks) bound together by gluons (with a few exceptions with no quarks, such aspositroniumandmuonium). Those containing few (≤ 5) quarks (including antiquarks) are calledhadrons.Due to a property known ascolor confinement,quarks are never found singly but always occur in hadrons containing multiple quarks. The hadrons are divided by number of quarks (including antiquarks) into thebaryonscontaining an odd number of quarks (almost always 3), of which theprotonandneutron(the twonucleons) are by far the best known; and themesonscontaining an even number of quarks (almost always 2, one quark and one antiquark), of which thepionsandkaonsare the best known.
Except for the proton and neutron, all other hadrons are unstable and decay into other particles in microseconds or less. A proton is made of twoup quarksand onedown quark,while the neutron is made of two down quarks and one up quark. These commonly bind together into an atomic nucleus, e.g. a helium-4 nucleus is composed of two protons and two neutrons. Most hadrons do not live long enough to bind into nucleus-like composites; those that do (other than the proton and neutron) formexotic nuclei.
By statistics
editAny subatomic particle, like any particle in thethree-dimensional spacethat obeys thelawsofquantum mechanics,can be either a boson (with integerspin) or a fermion (with odd half-integer spin).
In the Standard Model, all the elementary fermions have spin 1/2, and are divided into the quarks which carrycolor chargeand therefore feel the strong interaction, and theleptonswhich do not. The elementary bosons comprise the gauge bosons (photon, W and Z, gluons) with spin 1, while the Higgs boson is the only elementary particle with spin zero.
The hypothetical graviton is required theoretically to have spin 2, but is not part of the Standard Model. Some extensions such assupersymmetrypredict additional elementary particles with spin 3/2, but none have been discovered as of 2023.
Due to the laws for spin of composite particles, the baryons (3 quarks) have spin either 1/2 or 3/2 and are therefore fermions; the mesons (2 quarks) have integer spin of either 0 or 1 and are therefore bosons.
By mass
editInspecial relativity,theenergy of a particle at rest equals its mass times the speed of light squared,E=mc2.That is,masscan be expressed in terms ofenergyand vice versa. If a particle has aframe of referencein which it liesat rest,then it has a positiverest massand is referred to asmassive.
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 (thetau particle) is heavier than the two lightest flavours of baryons (nucleons). It is also certain that any particle with anelectric chargeis massive.
When originally defined in the 1950s, the terms baryons, mesons and leptons referred to masses; however, after the quark model became accepted in the 1970s, it was recognised that baryons are composites of three quarks, mesons are composites of one quark and one antiquark, while leptons are elementary and are defined as the elementary fermions with no color charge.
Allmassless particles(particles whoseinvariant massis zero) are elementary. These include the photon and gluon, although the latter cannot be isolated.
By decay
editMost subatomic particles are not stable. All leptons, as well as baryonsdecayby either the strong force or weak force (except for the proton). Protons are not known todecay,although whether they are "truly" stable is unknown, as some very important Grand Unified Theories (GUTs) actually require it. The μ and τ muons, as well as their antiparticles, decay by the weak force. Neutrinos (and antineutrinos) do not decay, but a related phenomenon ofneutrino oscillationsis thought to exist even in vacuums. The electron and its antiparticle, thepositron,are theoretically stable due tocharge conservationunless a lighter particle havingmagnitudeof electric charge≤eexists (which is unlikely). Its charge is not shown yet.
Other properties
editAll observable subatomic particles have their electric charge anintegermultiple of theelementary charge.The Standard Model's quarks have "non-integer" electric charges, namely, multiple of1/3e,but quarks (and other combinations with non-integer electric charge) cannot be isolated due tocolor confinement.For baryons, mesons, and their antiparticles the constituent quarks' charges sum up to an integer multiple ofe.
Through the work ofAlbert Einstein,Satyendra Nath Bose,Louis de Broglie,and many others, current scientific theory holds thatallparticles also have a wave nature.[10]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.[11]
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 ofconservation of energyandconservation of momentum,which let us make calculations of particle interactions on scales of magnitude that range from stars to quarks.[12]These are the prerequisite basics ofNewtonian mechanics,a series of statements and equations inPhilosophiae Naturalis Principia Mathematica,originally published in 1687.
Dividing an atom
editThe negatively charged electron has a mass of about1/1836of that of ahydrogenatom. The remainder of the hydrogen atom's mass comes from the positively chargedproton.Theatomic numberof an element is the number of protons in its nucleus. Neutrons are neutral particles having a mass slightly greater than that of the proton. Differentisotopesof the same element contain the same number of protons but different numbers of neutrons. Themass numberof an isotope is the total number ofnucleons(neutrons and protons collectively).
Chemistryconcerns itself with how electron sharing binds atoms into structures such as crystals andmolecules.The subatomic particles considered important in the understanding of chemistry are theelectron,theproton,and theneutron.Nuclear physicsdeals with how protons and neutrons arrange themselves in nuclei. The study of subatomic particles, atoms and molecules, and their structure and interactions, requiresquantum mechanics.Analyzing processes that change the numbers and types of particles requiresquantum field theory.The study of subatomic particlesper seis calledparticle physics.The termhigh-energy physicsis nearly synonymous to "particle physics" since creation of particles requires high energies: it occurs only as a result ofcosmic rays,or inparticle accelerators.Particle phenomenologysystematizes the knowledge about subatomic particles obtained from these experiments.[13]
History
editThe term "subatomicparticle "is largely aretronymof the 1960s, used to distinguish a large number ofbaryonsandmesons(which comprisehadrons) from particles that are now thought to betruly elementary.Before that hadrons were usually classified as "elementary" because their composition was unknown.
A list of important discoveries follows:
| Particle | Composition | Theorized | Discovered | Comments |
|---|---|---|---|---|
| electron e− |
elementary (lepton) | G. Johnstone Stoney(1874)[14] | J. J. Thomson(1897)[15] | Minimum unit of electrical charge, for which Stoney suggested the name in 1891.[16]First subatomic particle to be identified.[17] |
| Alpha particle α |
composite (atomic nucleus) | never | Ernest Rutherford(1899)[18] | Proven by Rutherford andThomas Roydsin 1907 to be helium nuclei. Rutherford won the Nobel Prize for Chemistry in 1908 for this discovery.[19] |
| photon γ |
elementary (quantum) | Max Planck(1900)[20] | Albert Einstein(1905)[21] | Necessary to solve thethermodynamicproblem ofblack-body radiation. |
| proton p |
composite (baryon) | William Prout (1815)[22] | Ernest Rutherford (1919, named 1920)[23][24] | The nucleus of1 H . |
| neutron n |
composite (baryon) | Ernest Rutherford (c.1920[25]) | James Chadwick(1932)[26] | The secondnucleon. |
| antiparticles | Paul Dirac(1928)[27] | Carl D. Anderson( e+ ,1932) |
Revised explanation usesCPT symmetry. | |
| pions π |
composite (mesons) | Hideki Yukawa(1935) | César Lattes,Giuseppe Occhialini,Cecil Powell(1947) | Explains thenuclear forcebetween nucleons. The first meson (by modern definition) to be discovered. |
| muon μ− |
elementary (lepton) | never | Carl D. Anderson (1936)[28] | Called a "meson" at first; but today classed as alepton. |
| kaons K |
composite (mesons) | never | G. D. Rochester,C. C. Butler(1947)[29] | Discovered incosmic rays.The firststrange particle. |
| lambda baryons Λ |
composite (baryons) | never | University of Melbourne( Λ0 ,1950)[30] |
The firsthyperondiscovered. |
| neutrino ν |
elementary (lepton) | Wolfgang Pauli(1930), named byEnrico Fermi | Clyde Cowan,Frederick Reines( ν e,1956) |
Solved the problem of energyspectrumofbeta decay. |
| quarks ( u , d , s ) |
elementary | Murray Gell-Mann,George Zweig(1964) | No particular confirmation event for thequark model. | |
| charm quark c |
elementary (quark) | Sheldon Glashow,John Iliopoulos,Luciano Maiani(1970) | B. Richter,S. C. C. Ting( J/ψ ,1974) |
|
| bottom quark b |
elementary (quark) | Makoto Kobayashi,Toshihide Maskawa(1973) | Leon M. Lederman( ϒ ,1977) |
|
| gluons | elementary (quantum) | Harald Fritzsch,Murray Gell-Mann(1972)[31] | DESY(1979) | |
| weak gauge bosons W± , Z0 |
elementary (quantum) | Glashow,Weinberg,Salam(1968) | CERN(1983) | Properties verified through the 1990s. |
| top quark t |
elementary (quark) | Makoto Kobayashi,Toshihide Maskawa(1973)[32] | Fermilab(1995)[33] | Does nothadronize,but is necessary to complete the Standard Model. |
| Higgs boson | elementary (quantum) | Peter Higgs(1964)[34][35] | CERN (2012)[36] | Thought to be confirmed in 2013. More evidence found in 2014.[37] |
| tetraquark | composite | ? | Zc(3900),2013,yet to be confirmed as a tetraquark | A new class of hadrons. |
| pentaquark | composite | ? | Yet another class of hadrons. As of 2019[update]several are thought to exist. | |
| graviton | elementary (quantum) | Albert Einstein (1916) | Interpretation of agravitational waveas particles is controversial.[38] | |
| magnetic monopole | elementary (unclassified) | Paul Dirac (1931)[39] | undiscovered | |
See also
editReferences
edit- ^"Subatomic particles".NTD. Archived fromthe originalon 16 February 2014.Retrieved5 June2012.
- ^Bolonkin, Alexander (2011).Universe, Human Immortality and Future Human Evaluation.Elsevier.p. 25.ISBN9780124158016.
- ^ Fritzsch, Harald (2005).Elementary Particles.World Scientific.pp.11–20.ISBN978-981-256-141-1.
- ^Hunter, Geoffrey; Wadlinger, Robert L. P. (August 23, 1987). Honig, William M.; Kraft, David W.; Panarella, Emilio (eds.).Quantum Uncertainties: Recent and Future Experiments and Interpretations.Springer US. pp. 331–343.doi:10.1007/978-1-4684-5386-7_18– via Springer Link.
The finite-field model of the photon is both a particle and a wave, and hence we refer to it by Eddington's name "wavicle".
- ^Heisenberg, W. (1927). "Über den anschaulichen Inhalt der quantentheoretischen Kinematik und Mechanik".Zeitschrift für Physik(in German).43(3–4): 172–198.Bibcode:1927ZPhy...43..172H.doi:10.1007/BF01397280.S2CID122763326.
- ^ Arndt, Markus; Nairz, Olaf; Vos-Andreae, Julian; Keller, Claudia; Van Der Zouw, Gerbrand; Zeilinger, Anton (2000). "Wave-particle duality of C60 molecules".Nature.401(6754): 680–682.Bibcode:1999Natur.401..680A.doi:10.1038/44348.PMID18494170.S2CID4424892.
- ^"What is a Particle?".12 November 2020.
- ^ Cottingham, W. N.; Greenwood, D.A. (2007).An introduction to the standard model of particle physics.Cambridge University Press.p. 1.ISBN978-0-521-85249-4.
- ^Okun, Lev(1962). "The theory of weak interaction".Proceedings of 1962 International Conference on High-Energy Physics at CERN.International Conference on High-Energy Physics (plenary talk). CERN, Geneva, CH. p. 845.Bibcode:1962hep..conf..845O.
- ^ Greiner, Walter (2001).Quantum Mechanics: An Introduction.Springer.p. 29.ISBN978-3-540-67458-0.
- ^
Eisberg, R. & Resnick, R. (1985).Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles(2nd ed.).John Wiley & Sons.pp.59–60.ISBN978-0-471-87373-0.
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.
- ^Newton, Isaac (1687). "Axioms or Laws of Motion".The Mathematical Principles of Natural Philosophy.England.
- ^Taiebyzadeh, Payam (2017).String Theory: A Unified Theory and Inner Dimension Of Elementary Particles (Baz Dahm).Iran: Shamloo Publications.ISBN978-6-00-116684-6.
- ^ Stoney, G. Johnstone (1881)."LII. On the physical units of nature".The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science.11(69): 381–390.doi:10.1080/14786448108627031.ISSN1941-5982.
- ^ Thomson, J. J. (1897)."Cathode Rays".The Electrician.39:104.
- ^ Klemperer, Otto(1959). "Electron physics: The physics of the free electron".Physics Today.13(6): 64–66.Bibcode:1960PhT....13R..64K.doi:10.1063/1.3057011.
- ^ Alfred, Randy (April 30, 2012)."April 30, 1897: J.J. Thomson Announces the Electron... Sort Of".Wired.ISSN1059-1028.Retrieved2022-08-22.
- ^ Rutherford, E. (1899)."VIII. Uranium radiation and the electrical conduction produced by it".The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science.47(284): 109–163.doi:10.1080/14786449908621245.ISSN1941-5982.
- ^ "The Nobel Prize in Chemistry 1908".NobelPrize.org.Retrieved2022-08-22.
- ^ Klein, Martin J. (1961)."Max Planck and the beginnings of the quantum theory".Archive for History of Exact Sciences.1(5): 459–479.doi:10.1007/BF00327765.ISSN0003-9519.S2CID121189755.
- ^ Einstein, Albert (1905)."Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt".Annalen der Physik(in German).322(6): 132–148.Bibcode:1905AnP...322..132E.doi:10.1002/andp.19053220607.
- ^Lederman, Leon(1993).The God Particle.Delta.ISBN9780385312110.
- ^Rutherford, Ernest (1920)."The Stability of Atoms".Proceedings of the Physical Society of London.33(1): 389–394.Bibcode:1920PPSL...33..389R.doi:10.1088/1478-7814/33/1/337.ISSN1478-7814.
- ^There was early debate on what to name the proton as seen in the follow commentary articles bySoddy 1920andLodge 1920.
- ^Rutherford, Ernest (1920)."Bakerian Lecture: Nuclear constitution of atoms".Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character.97(686): 374–400.Bibcode:1920RSPSA..97..374R.doi:10.1098/rspa.1920.0040.ISSN0950-1207.
- ^Chadwick, J. (1932)."The existence of a neutron".Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character.136(830): 692–708.Bibcode:1932RSPSA.136..692C.doi:10.1098/rspa.1932.0112.ISSN0950-1207.
- ^Dirac, P. A. M. (1928)."The quantum theory of the electron".Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character.117(778): 610–624.Bibcode:1928RSPSA.117..610D.doi:10.1098/rspa.1928.0023.ISSN0950-1207.
- ^Anderson, Carl D.; Neddermeyer, Seth H. (1936-08-15)."Cloud Chamber Observations of Cosmic Rays at 4300 Meters Elevation and Near Sea-Level".Physical Review.50(4): 263–271.Bibcode:1936PhRv...50..263A.doi:10.1103/PhysRev.50.263.ISSN0031-899X.
- ^Rochester, G. D.; Butler, C. C. (December 1947). "Evidence for the Existence of New Unstable Elementary Particles".Nature.160(4077): 855–857.Bibcode:1947Natur.160..855R.doi:10.1038/160855a0.ISSN0028-0836.PMID18917296.S2CID33881752.
- ^Some sources such as"The Strange Quark".indicate 1947.
- ^ Fritzsch, Harald; Gell-Mann, Murray (1972). "Current algebra: Quarks and what else?".EConf.C720906V2: 135–165.arXiv:hep-ph/0208010.
- ^Kobayashi, Makoto; Maskawa, Toshihide (1973)."C P Violation in the Renormalizable Theory of Weak Interaction".Progress of Theoretical Physics.49(2): 652–657.Bibcode:1973PThPh..49..652K.doi:10.1143/PTP.49.652.hdl:2433/66179.ISSN0033-068X.S2CID14006603.
- ^Abachi, S.; Abbott, B.; Abolins, M.; Acharya, B. S.; Adam, I.; Adams, D. L.; Adams, M.; Ahn, S.; Aihara, H.; Alitti, J.; Álvarez, G.; Alves, G. A.; Amidi, E.; Amos, N.; Anderson, E. W. (1995-04-03)."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.hdl:1969.1/181526.ISSN0031-9007.PMID10057979.S2CID42826202.
- ^"Letters from the Past – A PRL Retrospective".Physical Review Letters.2014-02-12.Retrieved2022-08-22.
- ^Higgs, Peter W. (1964-10-19)."Broken Symmetries and the Masses of Gauge Bosons".Physical Review Letters.13(16): 508–509.Bibcode:1964PhRvL..13..508H.doi:10.1103/PhysRevLett.13.508.ISSN0031-9007.
- ^Aad, G.; Abajyan, T.; Abbott, B.; Abdallah, J.; Abdel Khalek, S.; Abdelalim, A.A.; Abdinov, O.; Aben, R.; Abi, B.; Abolins, M.; AbouZeid, O.S.; Abramowicz, H.; Abreu, H.; Acharya, B.S.; Adamczyk, L. (2012)."Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC".Physics Letters B.716(1): 1–29.arXiv:1207.7214.Bibcode:2012PhLB..716....1A.doi:10.1016/j.physletb.2012.08.020.S2CID119169617.
- ^"CERN experiments report new Higgs boson measurements".CERN.23 June 2014.
- ^Moskowitz, Clara (March 31, 2014)."Multiverse Controversy Heats Up over Gravitational Waves".Scientific American.Retrieved2022-08-22.
- ^Dirac, Paul A. M. (1931)."Quantised singularities in the electromagnetic field".Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character.133(821): 60–72.Bibcode:1931RSPSA.133...60D.doi:10.1098/rspa.1931.0130.ISSN0950-1207.
Further reading
editGeneral readers
edit- Feynman, Richard P.; Weinberg, Steven, eds. (2001).Elementary particles and the laws of physics: the 1986 Dirac memorial lectures(Repr ed.). Cambridge:Cambridge University Press.ISBN978-0-521-65862-1.
- Greene, Brian(2003).The elegant universe: superstrings, hidden dimensions, and the quest for the ultimate theory.New York; London, England: Norton.ISBN978-0-393-05858-1.
- Oerter, Robert (2006).The theory of almost everything: the Standard Model, the unsung triumph of modern physics.New York, New York:Pi Press.ISBN978-0-452-28786-0.
- Schumm, Bruce A. (2004).Deep down things: the breathtaking beauty of particle physics.Baltimore, Maryland:Johns Hopkins University Press.ISBN978-0-8018-7971-5.
- Veltman, Martinus(2003).Facts and mysteries in elementary particle physics.River Edge, New Jersey:World Scientific.ISBN978-981-238-148-4.
Textbooks
edit- Coughlan, Guy D.; Dodd, J. E.; Gripaios, Ben M. (2006).The ideas of particle physics: an introduction for scientists(3rd ed.). Cambridge:Cambridge University Press.ISBN978-0-521-67775-2.An undergraduate text for those not majoring in physics.
- Griffiths, David J.(2007).Introduction to elementary particles.Weinheim:Wiley.ISBN978-0-471-60386-3.
- Kane, Gordon L.(2017).Modern elementary particle physics(2nd ed.). Cambridge, England, United Kingdom; New York, New York, USA:Cambridge University Press.ISBN978-1-107-16508-3.
External links
edit