View source for Antimatter

{{Short description|Material composed of antiparticles}}
{{Distinguish|dark matter}}
{{Redirect|Anti-nucleus|the antibodies|Antinuclear antibody}}
{{Other uses}}
{{Use dmy dates|date=July 2020}}
[[File:PositronDiscovery.png|thumb|A [[cloud chamber]] photograph of the first observed [[positron]], 2 August 1932]]
{{Antimatter}}
{{Modern physics}}

In [[modern physics]], '''antimatter''' is defined as [[matter]] composed of the [[antiparticle]]s (or "partners") of the corresponding [[subatomic particle|particles]] in "ordinary" matter, and can be thought of as matter with reversed charge and parity, or going backward in time (see [[CPT symmetry]]). Antimatter occurs in natural processes like [[cosmic ray]] collisions and some types of [[radioactive decay]], but only a tiny fraction of these have successfully been bound together in experiments to form antiatoms. Minuscule numbers of antiparticles can be generated at [[particle accelerator]]s, but total artificial production has been only a few [[nanogram]]s.<ref>{{cite news|access-date=2018-11-08|title=Ten things you might not know about antimatter|url=https://www.symmetrymagazine.org/article/april-2015/ten-things-you-might-not-know-about-antimatter|newspaper=symmetry magazine|archive-date=8 November 2018|archive-url=https://web.archive.org/web/20181108224807/https://www.symmetrymagazine.org/article/april-2015/ten-things-you-might-not-know-about-antimatter|url-status=live}}</ref> No [[Macroscopic scale|macroscopic]] amount of antimatter has ever been assembled due to the extreme cost and difficulty of production and handling. Nonetheless, antimatter is an essential component of widely available applications related to [[beta decay]], such as [[positron emission tomography]], [[radiation therapy]],<ref>{{Cite journal |last1=Bittner |first1=Martin-Immanuel |last2=Grosu |first2=Anca-Ligia |last3=Wiedenmann |first3=Nicole |last4=Wilkens |first4=Jan J. |date=2014-01-16 |title=A systematic review of antiproton radiotherapy |journal=Frontiers in Physics |language=English |volume=1 |doi=10.3389/fphy.2013.00037 |doi-access=free |issn=2296-424X}}</ref> and industrial imaging.

In theory, a particle and its antiparticle (for example, a [[proton]] and an [[antiproton]]) have the same [[mass]], but opposite [[electric charge]], and other differences in [[quantum number]]s.

A collision between any particle and its anti-particle partner leads to their mutual [[annihilation]], giving rise to various proportions of intense [[photon]]s ([[gamma ray]]s), [[neutrino]]s, and sometimes less-massive particle{{ndash}}antiparticle pairs. The majority of the total energy of annihilation emerges in the form of [[ionizing radiation]]. If surrounding matter is present, the energy content of this radiation will be absorbed and converted into other forms of energy, such as heat or light. The amount of energy released is usually proportional to the total mass of the collided matter and antimatter, in accordance with the [[mass–energy equivalence]] equation, {{math|{{nowrap|''E''{{=}}''mc''<sup>2</sup>}}}}.<ref>{{cite web |date=11 August 2011 |title=Smidgen of Antimatter Surrounds Earth |work=Discovery News |url=http://news.discovery.com/space/pamela-spots-a-smidgen-of-antimatter-110811.html |archive-url=https://web.archive.org/web/20110926174944/http://news.discovery.com/space/pamela-spots-a-smidgen-of-antimatter-110811.html |archive-date=26 September 2011|url-status=live}}</ref>

Antiparticles bind with each other to form antimatter, just as ordinary particles bind to form normal matter. For example, a [[positron]] (the antiparticle of the [[electron]]) and an antiproton (the antiparticle of the proton) can form an [[antihydrogen]] atom. The [[Atomic nucleus|nuclei]] of [[#Antihelium|antihelium]] have been artificially produced, albeit with difficulty, and are the most complex anti-nuclei so far observed.<ref>{{cite journal |last=Agakishiev |first=H. |display-authors=etal |collaboration=STAR Collaboration |date=2011 |title=Observation of the antimatter helium-4 nucleus |journal=[[Nature (journal)|Nature]] |volume=473 |issue=7347 |pages=353–356 |arxiv=1103.3312 |bibcode=2011Natur.473..353S |doi=10.1038/nature10079 |pmid=21516103|s2cid=118484566 }}</ref> Physical principles indicate that complex antimatter atomic nuclei are possible, as well as anti-atoms corresponding to the known chemical elements.

There is strong evidence that the [[observable universe]] is composed almost entirely of ordinary matter, as opposed to an equal mixture of matter and antimatter.<ref>{{cite journal |last=Canetti |first=L. |display-authors=etal |date=2012 |title=Matter and Antimatter in the Universe |journal=New J. Phys. |volume=14 |issue=9 |article-number=095012 |arxiv=1204.4186 |doi=10.1088/1367-2630/14/9/095012 |bibcode=2012NJPh...14i5012C|s2cid=119233888 }}</ref> This [[baryon asymmetry|asymmetry of matter and antimatter]] in the visible universe is one of the great [[unsolved problems in physics]].<ref>{{Cite web |last=Tenenbaum |first=David |date=28 December 2012 |title=One step closer: UW-Madison scientists help explain scarcity of antimatter |url=http://www.news.wisc.edu/21376 |work=University of Wisconsin–Madison News |archive-url=https://web.archive.org/web/20121228043843/http://www.news.wisc.edu/21376|archive-date=28 December 2012}}</ref> The process by which this inequality between matter and antimatter particles is hypothesised to have occurred is called [[baryogenesis]].

==Definitions==
Antimatter particles carry the same charge as matter particles, but of opposite sign. That is, an antiproton is negatively charged and an antielectron ([[positron]]) is positively charged. Neutrons do not carry a net charge, but their constituent [[quark]]s do. Protons and neutrons have a [[baryon number]] of +1, while antiprotons and antineutrons have a baryon number of –1. Similarly, electrons have a [[lepton number]] of +1, while that of positrons is –1. When a particle and its corresponding antiparticle collide, they are both converted into energy.<ref>
{{cite journal
 |last=Tsan |first=Ung Chan
 |date=2013
 |title=Mass, Matter, Materialization, Mattergenesis and Conservation of Charge
 |journal=International Journal of Modern Physics E
 |volume=22 |issue=5 |page=1350027
 |bibcode=2013IJMPE..2250027T
 |doi=10.1142/S0218301313500274
 |quote=Matter conservation means conservation of baryonic number ''A'' and leptonic number ''L'', ''A'' and ''L'' being algebraic numbers. Positive ''A'' and ''L'' are associated to matter particles, negative ''A'' and ''L'' are associated to antimatter particles. All known interactions do conserve matter.
}}</ref><ref>{{cite journal
 |last=Tsan |first=U. C.
 |date=2012
 |title=Negative Numbers And Antimatter Particles
 |journal=International Journal of Modern Physics E
 |volume=21 |issue=1 |pages=1250005-1–1250005-23
 |bibcode=2012IJMPE..2150005T
 |doi=10.1142/S021830131250005X
 |quote=Antimatter particles are characterized by negative baryonic number ''A'' or/and negative leptonic number ''L''. Materialization and annihilation obey conservation of ''A'' and ''L'' (associated to all known interactions).
}}</ref><ref name="Dirac-1933">{{Cite book
 |last=Dirac
 |first=Paul A. M.
 |year=1965
 |title=Physics Nobel Lectures
 |volume=12
 |pages=320–325
 |location=Amsterdam-London-New York
 |publisher=Elsevier
 |url=https://assets.nobelprize.org/uploads/2018/06/dirac-lecture.pdf
 |access-date=10 October 2019
 |archive-date=10 October 2019
 |archive-url=https://web.archive.org/web/20191010172411/https://assets.nobelprize.org/uploads/2018/06/dirac-lecture.pdf
 |url-status=live
 }}</ref>

The [[French language|French]] term for "made of or pertaining to antimatter", {{wikt-lang|en|contraterrene}}, led to the initialism "C.T." and the science fiction term {{wikt-lang|en|seetee}},<ref>{{Cite encyclopedia |title=Antimatter |encyclopedia=Science Fiction Encyclopedia |url=http://www.sf-encyclopedia.com/entry/antimatter |access-date=10 October 2019 |archive-date=28 July 2019 |archive-url=https://web.archive.org/web/20190728050510/http://sf-encyclopedia.com/entry/antimatter |url-status=live }}</ref> as used in such novels as ''[[Seetee Ship]]''.<ref>{{Cite journal|last=McCaffery |first=Larry |title=An Interview with Jack Williamson |journal=Science Fiction Studies |volume=18 |issue=54 |date=July 1991 |pages=230–252 |doi=10.1525/sfs.18.2.230 |url=https://www.depauw.edu/sfs/interviews/williamson54interview.htm |archive-url=https://web.archive.org/web/20060912123849/https://www.depauw.edu/sfs/interviews/williamson54interview.htm |archive-date=12 September 2006 |url-status=live }}</ref>

==Conceptual history==
The idea of [[negative matter]] appears in past theories of matter that have now been abandoned. Using the once popular [[vortex theory of gravity]], the possibility of matter with negative gravity was discussed by [[William Mitchinson Hicks|William Hicks]] in the 1880s. Between the 1880s and the 1890s, [[Karl Pearson]] proposed the existence of "squirts"<ref>
{{cite journal
 |last=Pearson |first=K.
 |date=1891
 |title=Ether Squirts
 |journal=[[American Journal of Mathematics]]
 |volume=13 |issue=4 |pages=309–72
 |doi=10.2307/2369570
 |jstor=2369570
}}</ref> and sinks of the flow of [[Luminiferous aether|aether]]. The squirts represented normal matter and the sinks represented negative matter. Pearson's theory required a fourth dimension for the aether to flow from and into.<ref>
{{cite book
 |last=Kragh |first=H.
 |date=2002
 |title=Quantum Generations: A History of Physics in the Twentieth Century
 |pages=5–6
 |publisher=[[Princeton University Press]]
 |isbn=978-0-691-09552-3
}}</ref>

The term antimatter was first used by [[Arthur Schuster]] in two rather whimsical letters to ''[[Nature (journal)|Nature]]'' in 1898,<ref>{{cite journal
 |last=Schuster
 |first=A.
 |date=1898
 |title=Potential Matter – A Holiday Dream
 |journal=[[Nature (journal)|Nature]]
 |volume=58
 |issue=1503
 |page=367
 |bibcode=1898Natur..58..367S
 |doi=10.1038/058367a0
 |s2cid=4046342
 |url=https://zenodo.org/record/1429382
 |doi-access=free
 |access-date=31 August 2020
 |archive-date=10 October 2021
 |archive-url=https://web.archive.org/web/20211010050639/https://zenodo.org/record/1429382
 |url-status=live
 }}</ref> in which he coined the term. He hypothesized antiatoms, as well as whole antimatter solar systems, and discussed the possibility of matter and antimatter annihilating each other. Schuster's ideas were not a serious theoretical proposal, merely speculation, and like the previous ideas, differed from the modern concept of antimatter in that it possessed [[antigravity|negative gravity]].<ref>{{cite book
 |last=Harrison
 |first=E. R.
 |date=2000-03-16
 |title=Cosmology: The Science of the Universe
 |url=https://books.google.com/books?id=wzpKc3bZqDoC
 |edition=2nd
 |pages=266, 433
 |publisher=[[Cambridge University Press]]
 |isbn=978-0-521-66148-5
 |access-date=31 August 2020
 |archive-date=10 October 2021
 |archive-url=https://web.archive.org/web/20211010050640/https://books.google.com/books?id=wzpKc3bZqDoC
 |url-status=live
 }}</ref>

The modern theory of antimatter began in 1928, with a paper<ref>
{{cite journal
 |last=Dirac |first=P. A. M.
 |date=1928
 |title=The Quantum Theory of the Electron
 |journal=[[Proceedings of the Royal Society A]]
 |volume=117 |issue=778 |pages=610–624
 |bibcode=1928RSPSA.117..610D
 |doi=10.1098/rspa.1928.0023
 |jstor=94981
 |doi-access=free
 }}</ref> by [[Paul Dirac]]. Dirac realised that his [[Dirac equation|relativistic version]] of the [[Schrödinger equation|Schrödinger wave equation]] for electrons predicted the possibility of [[antielectron]]s. Although Dirac had laid the groundwork for the existence of these "antielectrons" he initially failed to pick up on the implications contained within his own equation. He freely gave the credit for that insight to [[J. Robert Oppenheimer]], whose seminal paper "On the Theory of Electrons and Protons" (Feb 14th 1930) drew on Dirac's equation and argued for the existence of a positively charged electron (a positron), which as a counterpart to the electron should have the same mass as the electron itself. This meant that it could not be, as Dirac had in fact suggested, a proton. Dirac further postulated the existence of antimatter in a 1931 paper which referred to the positron as an "anti-electron".<ref>{{Cite journal |last=Dirac |first=Paul |date=1931 |title=Quantised singularities in the electromagnetic field |journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character |language=en |volume=133 |issue=821 |pages=60–72 |bibcode=1931RSPSA.133...60D |doi=10.1098/rspa.1931.0130 |issn=0950-1207|doi-access=free }}</ref><ref name=":3">{{Cite web |title=Discovering the positron |url=https://timeline.web.cern.ch/timeline-header/142#416 |access-date=2023-10-23 |website=timeline.web.cern.ch}}</ref> These were discovered by [[Carl David Anderson|Carl D. Anderson]] in 1932 and named [[positron]]s from "positive electron". Although Dirac did not himself use the term antimatter, its use follows on naturally enough from antielectrons, antiprotons, etc.<ref>
{{cite book
 |last1=Kaku |first1=M.
 |last2=Thompson |first2=J. T.
 |date=1997
 |title=Beyond Einstein: The Cosmic Quest for the Theory of the Universe
 |pages=179–180
 |publisher=[[Oxford University Press]]
 |isbn=978-0-19-286196-2
}}</ref> 

The [[Feynman–Stueckelberg interpretation]] states that [[antiparticles]] obey the same equations of motion as regular particles but with charge, parity and time inverted. This allows analysis of antiparticles using [[Feynman diagram]]s with time reversed.<ref>
{{cite book
 |last=Griffiths |first=D. J. 
 |author-link=David J. Griffiths 
 |page=61 
 |year=2008 
 |title=Introduction to Elementary Particles 
 |edition=2nd 
 |publisher=[[John Wiley & Sons]] 
 |isbn=978-3-527-40601-2
}}</ref>

==Notation==
One way to denote an [[antiparticle]] is by adding a bar over the particle's symbol. For example, the proton and antiproton are denoted as {{Subatomic particle|proton}} and {{Subatomic particle|antiproton}}, respectively. The same rule applies if one were to address a particle by its constituent components. A proton is made up of  {{Subatomic particle|link=yes|Up quark}} {{Subatomic particle|link=no|Up quark}} {{Subatomic particle|link=yes|Down quark}} [[quark]]s, so an antiproton must therefore be formed from {{Subatomic particle|link=yes|Up antiquark}} {{Subatomic particle|link=no|Up antiquark}} {{Subatomic particle|link=yes|Down antiquark}} [[antiquark]]s. Another convention is to distinguish particles by positive and negative [[electric charge]]. Thus, the electron and positron are denoted simply as {{Subatomic particle|Electron}} and {{Subatomic particle|Positron}} respectively. To prevent confusion, however, the two conventions are never mixed.

==Properties==
There is no difference in the gravitational behavior of matter and antimatter. In other words, antimatter falls down when dropped, not up. This was confirmed with the thin, very cold gas of thousands of [[antihydrogen]] atoms that were confined in a vertical shaft surrounded by superconducting electromagnetic coils. These can create a [[Magnetic mirror|magnetic bottle]] to keep the antimatter from coming into contact with matter and annihilating. The researchers then gradually weakened the magnetic fields and detected the antiatoms using two sensors as they escaped and annihilated. Most of the anti-atoms came out of the bottom opening, and only one-quarter out of the top.<ref>
{{cite journal
 |last1=Castelvecchi |first1=D.
 |date= 5 October 2023
 |title=Antimatter falls down, not up
 |journal=Nature
 |volume=622
 |issue=7981
 |pages=14–15
 |doi=10.1038/d41586-023-03043-0
 |pmid=37759123
 |s2cid=263121330
 }}</ref>

There are compelling theoretical reasons to believe that, aside from the fact that antiparticles have different signs on all charges (such as electric and baryon charges), matter and antimatter have exactly the same properties.<ref>
{{Cite arXiv
 |last1=Dolgov |first1=A. D.
 |year=2002
 |title=Cosmological Matter-Antimatter Asymmetry and Antimatter in the Universe
 |eprint=hep-ph/0211260
}}</ref><ref>This is a consequence of the [[CPT theorem]]</ref> This means a particle and its corresponding antiparticle must have identical masses and decay lifetimes (if unstable). It also implies that, for example, a star made up of antimatter (an "antistar") will shine just like an ordinary star.<ref name="Dirac-1933b">As Dirac said in 1933 ''It is quite possible that for some of the stars it is the other way about, these stars being built up mainly of positrons and negative protons. In fact, there may be half the stars of each kind. The two kinds of stars would both show exactly the same spectra, and there would be no way of distinguishing them by present astronomical methods.'' {{harvnb|Dirac|1965|page=325}}</ref> This idea was tested experimentally in 2016 by the [[ALPHA experiment|ALPHA]] experiment, which measured the transition between the two lowest energy states of [[antihydrogen]]. The results, which are identical to that of hydrogen, confirmed the validity of quantum mechanics for antimatter.<ref>
{{cite journal
 |last1=Castelvecchi |first1=D.
 |date=19 December 2016
 |title=Ephemeral antimatter atoms pinned down in milestone laser test
 |journal=Nature
 |doi=10.1038/nature.2016.21193
|s2cid=125464517
 }}</ref><ref>
{{cite journal
 |last=Ahmadi |first=M
 |display-authors=etal
 |date=19 December 2016
 |title=Observation of the 1S–2S transition in trapped antihydrogen
 |journal=Nature
 |volume=541 |issue=7638 |pages=506–510
 |bibcode=2017Natur.541..506A
 |doi=10.1038/nature21040
 |pmid=28005057
|doi-access=free
 |hdl=1828/11655
 |hdl-access=free
 }}</ref>

==Origin and asymmetry==
{{see also|Baryogenesis}}

{{multiple image
|align=right
|direction=horizontal
|image2=Antimatter Explosions.ogv
|width2=232
|caption2=There are some 500 terrestrial [[gamma ray]] flashes daily. The red dots show those spotted by the [[Fermi Gamma-ray Space Telescope]] in 2010. The blue areas indicate where potential lightning can occur for terrestrial [[gamma ray]] flashes. |image1=Antimatter Explosions 2.ogv
|width1=232
|caption1=A video showing how scientists used the Fermi Gamma ray Space Telescope's gamma ray detector to uncover bursts of antimatter from thunderstorms}}

Most things observable from the Earth seem to be made of matter rather than antimatter. If antimatter-dominated regions of space existed, the gamma rays produced in annihilation reactions along the boundary between matter and antimatter regions would be detectable.<ref>{{cite journal
 |last=Sather
 |first=E.
 |date=1999
 |title=The Mystery of the Matter Asymmetry
 |url=http://www.slac.stanford.edu/pubs/beamline/26/1/26-1-sather.pdf
 |journal={{ill|Beam Line|wd=Q136671063|s=1|v=sup}}
 |volume=26
 |issue=1
 |pages=31–37
 |access-date=22 June 2008
 |archive-date=12 October 2008
 |archive-url=https://web.archive.org/web/20081012012543/http://www.slac.stanford.edu/pubs/beamline/26/1/26-1-sather.pdf
 |url-status=live
 }}</ref>

Antiparticles are created everywhere in the [[universe]] where high-energy particle collisions take place. High-energy [[cosmic ray]]s striking [[Earth's atmosphere]] (or any other matter in the [[Solar System]]) produce minute quantities of antiparticles in the resulting [[particle jet]]s, which are immediately annihilated by contact with nearby matter. They may similarly be produced in regions like the [[Galactic Center|center]] of the [[Milky Way]] and other galaxies, where very energetic celestial events occur (principally the interaction of [[relativistic jet]]s with the [[interstellar medium]]). The presence of the resulting antimatter is detectable by the two [[gamma ray]]s produced every time [[positron]]s annihilate with nearby matter. The [[frequency]] and [[wavelength]] of the gamma rays indicate that each carries 511&nbsp;[[electronvolt|keV]] of energy (that is, the [[rest mass]] of an [[electron]] multiplied by ''[[speed of light|c]]''<sup>2</sup>).

Observations by the [[European Space Agency]]'s [[INTEGRAL|INTEGRAL satellite]] may explain the origin of a giant antimatter cloud surrounding the Galactic Center. The observations show that the cloud is asymmetrical and matches the pattern of [[X-ray binaries]] (binary star systems containing black holes or neutron stars), mostly on one side of the Galactic Center. While the mechanism is not fully understood, it is likely to involve the production of electron–positron pairs, as ordinary matter gains kinetic energy while falling into a [[stellar remnant]].<ref>
{{cite web
 |date=9 January 2008
 |title=Integral discovers the galaxy's antimatter cloud is lopsided
 |url=http://www.esa.int/esaCP/SEMKTX2MDAF_index_0.html
 |publisher=[[European Space Agency]]
 |access-date=24 May 2008
 |archive-url=https://web.archive.org/web/20080618215031/http://www.esa.int/esaCP/SEMKTX2MDAF_index_0.html
 |archive-date=18 June 2008
 |url-status=live
}}</ref><ref>
 {{cite journal
 |last=Weidenspointner |first=G.
 |display-authors=etal
 |date=2008
 |title=An asymmetric distribution of positrons in the Galactic disk revealed by γ-rays
 |journal=[[Nature (journal)|Nature]]
 |volume=451 |issue=7175 |pages=159–162
 |bibcode=2008Natur.451..159W
 |doi=10.1038/nature06490
 |pmid=18185581
|s2cid=4333175
 }}</ref>

Antimatter may exist in relatively large amounts in far-away galaxies due to [[cosmic inflation]] in the primordial time of the universe. Antimatter galaxies, if they exist, are expected to have the same chemistry and [[spectroscopy|absorption and emission spectra]] as normal-matter galaxies, and their [[astronomical object]]s would be observationally identical, making them difficult to distinguish.<ref>{{cite book
 |last=Close |first=F. E.
 |date=2009
 |title=Antimatter
 |page=114
 |publisher=Oxford University Press
 |isbn=978-0-19-955016-6
}}</ref> [[NASA]] is trying to determine if such galaxies exist by looking for X-ray and gamma ray signatures of annihilation events in [[colliding galaxy|colliding]] [[supercluster]]s.<ref>
{{cite web
 |date=30 October 2008
 |title=Searching for Primordial Antimatter
 |url=http://www.nasa.gov/mission_pages/chandra/news/08-160.html
 |publisher=[[NASA]]
 |access-date=18 June 2010
 |archive-url=https://web.archive.org/web/20100316213149/http://www.nasa.gov/mission_pages/chandra/news/08-160.html
 |archive-date=16 March 2010
 |url-status=live
}}</ref>

In October 2017, scientists working on the [[BASE experiment]] at [[CERN]] reported a measurement of the antiproton [[magnetic moment]] to a precision of 1.5 parts per billion.<ref name="TT-20171025">
{{cite web
 |last=Adamson |first=A.
 |date=19 October 2017
 |title=Universe Should Not Actually Exist: Big Bang Produced Equal Amounts of Matter And Antimatter
 |url=http://www.techtimes.com/articles/214821/20171025/universe-should-not-actually-exist-big-bang-produced-equal-amounts-of-matter-and-antimatter.htm
 |work=TechTimes.com
 |access-date=26 October 2017
 |archive-url=https://web.archive.org/web/20171026031017/http://www.techtimes.com/articles/214821/20171025/universe-should-not-actually-exist-big-bang-produced-equal-amounts-of-matter-and-antimatter.htm
 |archive-date=26 October 2017
 |url-status=live
}}</ref><ref name="NAT-20171020">
{{cite journal
 |last=Smorra |first=C.
 |display-authors=etal
 |date=20 October 2017
 |title=A parts-per-billion measurement of the antiproton magnetic moment
 |journal=[[Nature (journal)|Nature]]
 |volume=550 |issue=7676 |pages=371–374
 |doi=10.1038/nature24048
 |pmid=29052625
 |bibcode=2017Natur.550..371S
|doi-access=free
 }}</ref> It is consistent with the most precise measurement of the proton magnetic moment (also made by BASE in 2014), which supports the hypothesis of [[CPT symmetry]]. This measurement represents the first time that a property of antimatter is known more precisely than the equivalent property in matter.

Antimatter quantum interferometry has been first demonstrated in 2018 in the Positron Laboratory (L-NESS) of Rafael Ferragut<!--Q53261781--> in [[Como]] ([[Italy]]), by a group led by Marco Giammarchi.<ref>{{cite journal | doi = 10.1126/sciadv.aav7610 | volume=5 | title=First demonstration of antimatter wave interferometry | year=2019 | journal=Science Advances | article-number=eaav7610 | last1 = Sala | first1 = S. | last2 = Ariga | first2 = A. | last3 = Ereditato | first3 = A. | last4 = Ferragut | first4 = R. | last5 = Giammarchi | first5 = M. | last6 = Leone | first6 = M. | last7 = Pistillo | first7 = C. | last8 = Scampoli | first8 = P. | issue=5 | pmid = 31058223 | pmc = 6499593 | bibcode = 2019SciA....5.7610S}}</ref>

==Natural production==
{{main|Positron emission}}

Positrons are produced naturally in β<sup>+</sup> decays of naturally occurring radioactive isotopes (for example, [[potassium-40]]) and in interactions of gamma quanta (emitted by radioactive nuclei) with matter. [[Antineutrino]]s are another kind of antiparticle created by natural radioactivity (β<sup>−</sup> decay). Many different kinds of antiparticles are also produced by (and contained in) [[cosmic ray]]s. In January 2011, research by the [[American Astronomical Society]] discovered antimatter (positrons) originating above [[thunderstorm]] clouds; positrons are produced in terrestrial gamma ray flashes created by electrons accelerated by strong electric fields in the clouds.<ref>
{{cite web
 |date=11 January 2011
 |title=Antimatter caught streaming from thunderstorms on Earth
 |url=https://www.bbc.co.uk/news/science-environment-12158718
 |publisher=BBC
 |access-date=11 January 2011
 |archive-url=https://web.archive.org/web/20110112080623/http://www.bbc.co.uk/news/science-environment-12158718
 |archive-date=12 January 2011
 |url-status=live
}}</ref><ref>
{{Cite journal
 |title=Rogue Antimatter Found in Thunderclouds
 |volume=521
 |issue=7551
 |page=135
 |url=http://www.scientificamerican.com/article/rogue-antimatter-found-in-thunderclouds
 |access-date=2015-05-14
 |journal=[[Scientific American]]
 |url-status=live
 |archive-url=https://web.archive.org/web/20150514233632/http://www.scientificamerican.com/article/rogue-antimatter-found-in-thunderclouds/
 |archive-date=14 May 2015
|bibcode=2015Natur.521..135C
 |last1=Castelvecchi
 |first1=Davide
 |year=2015
 |doi=10.1038/521135a
 |pmid=25971485
 |doi-access=free
 }}</ref> [[Antiproton]]s have also been found to exist in the [[Van Allen radiation belt|Van Allen Belt]]s around the Earth by the [[Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics#Results|PAMELA module]],<ref>
{{cite journal
 |last1=Adriani |first1=O.
 |display-authors=etal
 |date=2011
 |title=The Discovery of Geomagnetically Trapped Cosmic-Ray Antiprotons
 |journal=The Astrophysical Journal
 |volume=737
 |issue=2
 |pages=L29
 |doi=10.1088/2041-8205/737/2/L29
|bibcode=2011ApJ...737L..29A
 |arxiv=1107.4882
 }}</ref><ref>
{{cite news
 |last=Than |first=Ker
 |date=10 August 2011
 |title=Antimatter Found Orbiting Earth – A First
 |url=http://news.nationalgeographic.com/news/2011/08/110810-antimatter-belt-earth-trapped-pamela-space-science/
 |publisher=[[National Geographic Society]]
 |access-date=12 August 2011
 |archive-url=https://web.archive.org/web/20111010014111/http://news.nationalgeographic.com/news/2011/08/110810-antimatter-belt-earth-trapped-pamela-space-science
 |archive-date=10 October 2011
 }}</ref> and similar antiproton belts may exist around Jupiter, Saturn, Neptune, and Uranus.<ref>{{Cite journal |last1=Spjeldvik |first1=Walther |last2=Bickford |first2=James |last3=Schmitt |first3=William |last4=Spjeldvik |first4=Walther |last5=Martin |first5=Inácio M. |last6=Pugacheva |first6=Galina |last7=Gusev |first7=Anatoly |date=2008 |title=Antiproton distributions around the Earth, Saturn and Jupiter from cosmic ray driven albedo antineutron decay |url=https://ui.adsabs.harvard.edu/abs/2008cosp...37.3002S/abstract |journal=37th COSPAR Scientific Assembly |language=en |volume=37 |pages=3002 |bibcode=2008cosp...37.3002S }}</ref><ref>{{Cite web |last=Cowen |first=Ron |date=2011-08-09 |title=Antimatter Belt Found Circling Earth |url=https://www.science.org/content/article/antimatter-belt-found-circling-earth |access-date=2025-10-27 |website=www.science.org |language=en}}</ref>

Antiparticles are also produced in any environment with a sufficiently high temperature (mean particle energy greater than the [[pair production]] threshold). It is hypothesized that during the period of baryogenesis, when the universe was extremely hot and dense, matter and antimatter were continually produced and annihilated. The presence of remaining matter, and absence of detectable remaining antimatter,<ref>
{{cite web
 |date=29 May 2000
 |title=What's the Matter with Antimatter?
 |url=https://science.nasa.gov/headlines/y2000/ast29may_1m.htm
 |publisher=[[NASA]]
 |access-date=24 May 2008
 |archive-url=https://web.archive.org/web/20080604155823/https://science.nasa.gov/headlines/y2000/ast29may_1m.htm
 |archive-date=4 June 2008
 }}</ref> is called [[baryon asymmetry]]. The exact mechanism that produced this asymmetry during baryogenesis remains an unsolved problem. One of the [[Sakharov conditions|necessary conditions]] for this asymmetry is the [[CP violation|violation of CP symmetry]], which has been experimentally observed in the [[weak interaction]].

Recent observations indicate black holes and neutron stars produce vast amounts of positron-electron plasma via the jets.<ref>
{{cite journal
 |url=http://pc.astro.brandeis.edu/pdfs/elec-pos.pdf
 |title=Electron-positron Jets Associated with Quasar 3C 279
 |journal=Nature
 |volume=395
 |issue=6701
 |page=457
 |url-status=live
 |archive-url=https://web.archive.org/web/20160404102941/http://pc.astro.brandeis.edu/pdfs/elec-pos.pdf
 |archive-date=4 April 2016
|bibcode=1998Natur.395..457W
 |last1=Wardle
 |first1=J. F. C.
 |last2=Homan
 |first2=D. C.
 |last3=Ojha
 |first3=R.
 |last4=Roberts
 |first4=D. H.
 |year=1998
 |doi=10.1038/26675
 |hdl=11603/17540
 |s2cid=4413709
 |hdl-access=free
 }}</ref><ref>
{{cite web
 |url=http://www.nasa.gov/centers/goddard/news/topstory/2007/antimatter_binary.html
 |title=NASA – Vast Cloud of Antimatter Traced to Binary Stars
 |url-status=live
 |archive-url=https://web.archive.org/web/20160307195428/http://www.nasa.gov/centers/goddard/news/topstory/2007/antimatter_binary.html
 |archive-date=7 March 2016}}</ref>

===Observation in cosmic rays===
{{main|Cosmic ray}}

Satellite experiments have found evidence of [[positron]]s and a few antiprotons in primary cosmic rays, amounting to less than 1% of the particles in primary cosmic rays. This antimatter cannot all have been created in the Big Bang, but is instead attributed to have been produced by cyclic processes at high energies. For instance, electron-positron pairs may be formed in [[pulsar]]s, as a magnetized neutron star rotation cycle shears electron-positron pairs from the star surface. Therein the antimatter forms a wind that crashes upon the ejecta of the progenitor supernovae. This weathering takes place as "the cold, magnetized relativistic wind launched by the star hits the non-relativistically expanding ejecta, a shock wave system forms in the impact: the outer one propagates in the ejecta, while a reverse shock propagates back towards the star."<ref>
{{cite journal
 |last1=Serpico |first1=P. D.
 |date=December 2012
 |title=Astrophysical models for the origin of the positron "excess"
 |journal=Astroparticle Physics
 |volume=39–40 |pages=2–11
 |arxiv=1108.4827
 |bibcode=2012APh....39....2S
 |doi=10.1016/j.astropartphys.2011.08.007
 |s2cid=59323641
 }}</ref> The former ejection of matter in the outer shock wave and the latter production of antimatter in the reverse shock wave are steps in a space weather cycle.

Preliminary results from the presently operating [[Alpha Magnetic Spectrometer]] (''AMS-02'') on board the [[International Space Station]] show that positrons in the cosmic rays arrive with no directionality, and with energies that range from 10 [[GeV]] to 250&nbsp;GeV. In September, 2014, new results with almost twice as much data were presented in a talk at CERN and published in Physical Review Letters.<ref>
{{cite journal
 |last=Accardo |first=L.
 |display-authors=etal
 |collaboration=AMS Collaboration
 |date=18 September 2014
 |title=High Statistics Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–500&nbsp;GeV with the Alpha Magnetic Spectrometer on the International Space Station
 |url=http://ams.nasa.gov/Documents/AMS_Publications/PhysRevLett.113.121101.pdf
 |journal=Physical Review Letters
 |volume=113 |issue=12 |article-number=121101
 |bibcode=2014PhRvL.113l1101A
 |doi=10.1103/PhysRevLett.113.121101
 |pmid=25279616
 |archive-url=https://web.archive.org/web/20141017131844/http://ams.nasa.gov/Documents/AMS_Publications/PhysRevLett.113.121101.pdf
 |archive-date=17 October 2014
 |url-status=live
|doi-access=free
 }}</ref><ref>{{Cite journal
 |last1=Schirber
 |first1=M.
 |year=2014
 |title=Synopsis: More Dark Matter Hints from Cosmic Rays?
 |url=https://cds.cern.ch/record/1756487
 |journal=Physical Review Letters
 |volume=113
 |issue=12
 |article-number=121102
 |arxiv=1701.07305
 |bibcode=2014PhRvL.113l1102A
 |doi=10.1103/PhysRevLett.113.121102
 |pmid=25279617
 |hdl=1721.1/90426
 |s2cid=2585508
 |access-date=22 August 2018
 |archive-date=29 November 2019
 |archive-url=https://web.archive.org/web/20191129164628/https://cds.cern.ch/record/1756487
 |url-status=live
 }}</ref> A new measurement of positron fraction up to 500&nbsp;GeV was reported, showing that positron fraction peaks at a maximum of about 16% of total electron+positron events, around an energy of 275 ± 32 GeV. At higher energies, up to 500&nbsp;GeV, the ratio of positrons to electrons begins to fall again. The absolute flux of positrons also begins to fall before 500&nbsp;GeV, but peaks at energies far higher than electron energies, which peak about 10 GeV.<ref>
{{cite web
 |title=New results from the Alpha Magnetic$Spectrometer on the International Space Station
 |url=http://ams.nasa.gov/Documents/AMS_Publications/ams_new_results_-_18.09.2014.pdf
 |website=AMS-02 at NASA
 |access-date=21 September 2014
 |archive-url=https://web.archive.org/web/20140923222913/http://ams.nasa.gov/Documents/AMS_Publications/ams_new_results_-_18.09.2014.pdf
 |archive-date=23 September 2014
 |url-status=live
}}</ref> These results on interpretation have been suggested to be due to positron production in annihilation events of massive [[dark matter]] particles.<ref name="physrevltrs413">
{{Cite journal
 |last1=Aguilar |first1=M.
 |date=2013
 |display-authors=etal
 |title=First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5–350 GeV
 |url=http://archive-ouverte.unige.ch/unige:40557
 |journal=Physical Review Letters
 |volume=110 |issue=14 |article-number=141102
 |bibcode=2013PhRvL.110n1102A
 |doi=10.1103/PhysRevLett.110.141102
 |pmid=25166975
 |archive-url=https://web.archive.org/web/20170419205517/https://archive-ouverte.unige.ch/unige:40557
 |archive-date=19 April 2017
 |url-status=live
|doi-access=free
 |hdl=1721.1/81241
 |hdl-access=free
 }}</ref>

Cosmic ray antiprotons also have a much higher energy than their normal-matter counterparts (protons). They arrive at Earth with a characteristic energy maximum of 2&nbsp;GeV, indicating their production in a fundamentally different process from cosmic ray protons, which on average have only one-sixth of the energy.<ref>
{{cite journal
 |last1=Moskalenko |first1=I. V.
 |last2=Strong |first2=A. W.
 |last3=Ormes |first3=J. F.
 |last4=Potgieter |first4=M. S.
 |date=January 2002
 |title=Secondary antiprotons and propagation of cosmic rays in the Galaxy and heliosphere
 |journal=The Astrophysical Journal
 |volume=565 |issue=1 |pages=280–296
 |arxiv=astro-ph/0106567
 |bibcode=2002ApJ...565..280M
 |doi=10.1086/324402
|s2cid=5863020
 }}</ref>

There is an ongoing search for larger antimatter nuclei, such as [[#Antihelium|antihelium]] nuclei (that is, anti-alpha particles), in cosmic rays. The detection of natural antihelium could imply the existence of large antimatter structures such as an antistar. A prototype of the ''AMS-02'' designated ''AMS-01'', was flown into space aboard the {{OV|103}} on [[STS-91]] in June 1998. By not detecting any [[#Antihelium|antihelium]] at all, the ''AMS-01'' established an upper limit of 1.1×10<sup>−6</sup> for the antihelium to helium [[flux]] ratio.<ref>
{{cite journal
 |last1=Aguilar |first1=M.
 |display-authors=etal
 |collaboration=AMS Collaboration
 |date=August 2002
 |title=The Alpha Magnetic Spectrometer (AMS) on the International Space Station: Part I – results from the test flight on the space shuttle
 |journal=Physics Reports
 |volume=366 |issue=6 |pages=331–405
 |bibcode=2002PhR...366..331A
 |doi=10.1016/S0370-1573(02)00013-3
 |hdl=2078.1/72661
|s2cid=122726107
 |hdl-access=free
 }}</ref> AMS-02 revealed in December 2016 that it had discovered a few signals consistent with antihelium nuclei amidst several billion helium nuclei. The result remains to be verified, and {{as of|2017|lc=y}}, the team is trying to rule out contamination.<ref>{{cite journal|url=https://www.science.org/content/article/giant-space-magnet-may-have-trapped-antihelium-raising-idea-lingering-pools-antimatter|title=Giant space magnet may have trapped antihelium, raising idea of lingering pools of antimatter in the cosmos|journal=Science|first=Joshua |last=Sokol|date=April 2017|doi=10.1126/science.aal1067|access-date=1 November 2019|archive-date=1 November 2019|archive-url=https://web.archive.org/web/20191101232343/https://www.sciencemag.org/news/2017/04/giant-space-magnet-may-have-trapped-antihelium-raising-idea-lingering-pools-antimatter|url-status=live|url-access=subscription}}</ref>

==Artificial production==

===Positrons===
{{Main|Positron}}

Positrons were reported<ref>
{{cite press release
 |publisher=[[Lawrence Livermore National Laboratory]]
 |date=3 November 2008
 |title=Billions of particles of anti-matter created in laboratory
 |url=https://phys.org/news/2008-11-billions-particles-anti-matter-laboratory.html
 |archive-url=https://web.archive.org/web/20151206012202/http://phys.org/news/2008-11-billions-particles-anti-matter-laboratory.html
 |archive-date=6 December 2015
 |access-date=19 November 2008
}}</ref> in November 2008 to have been generated by [[Lawrence Livermore National Laboratory]] in large numbers. A [[laser]] drove [[electrons]] through a [[gold]] target's [[atomic nucleus|nuclei]], which caused the incoming electrons to emit [[energy]] [[quantum|quanta]] that decayed into both matter and antimatter. Positrons were detected at a higher rate and in greater density than ever previously detected in a laboratory. Previous experiments made smaller quantities of positrons using lasers and paper-thin targets; newer simulations showed that short bursts of ultra-intense lasers and millimeter-thick gold are a far more effective source.<ref>
{{cite magazine
 |date=19 November 2008
 |title=Laser creates billions of antimatter particles
 |url=http://www.cosmosmagazine.com/news/2345/laser-creates-billions-particles-antimatter
 |magazine=[[Cosmos Magazine]]
 |access-date=1 July 2009
 |archive-url=https://web.archive.org/web/20090522151227/http://www.cosmosmagazine.com/news/2345/laser-creates-billions-particles-antimatter
 |archive-date=22 May 2009
 |url-status=live
}}</ref>

In 2023, the production of the first electron-positron beam-plasma was reported by a collaboration led by researchers at [[University of Oxford]] working with the [[High-Radiation to Materials]] (HRMT)<ref>{{Cite journal |last1=Efthymiopoulos |first1=I |last2=Hessler |first2=C |last3=Gaillard |first3=H |last4=Grenier |first4=D |last5=Meddahi |first5=M |last6=Trilhe |first6=P |last7=Pardons |first7=A |last8=Theis |first8=C |last9=Charitonidis |first9=N |last10=Evrard |first10=S |last11=Vincke |first11=H |last12=Lazzaroni |first12=M |date=2011|journal = 2nd International Particle Accelerator Conference |title=HiRadMat: A New Irradiation Facility for Material Testing at CERN |url=https://cds.cern.ch/record/1403043}}</ref> facility at [[CERN]].<ref name=":0">{{Cite journal |last1=Arrowsmith |first1=C. D. |last2=Simon |first2=P. |last3=Bilbao |first3=P. J. |last4=Bott |first4=A. F. A. |last5=Burger |first5=S. |last6=Chen |first6=H. |last7=Cruz |first7=F. D. |last8=Davenne |first8=T. |last9=Efthymiopoulos |first9=I. |last10=Froula |first10=D. H. |last11=Goillot |first11=A. |last12=Gudmundsson |first12=J. T. |last13=Haberberger |first13=D. |last14=Halliday |first14=J. W. D. |last15=Hodge |first15=T. |date=2024-06-12 |title=Laboratory realization of relativistic pair-plasma beams |journal=Nature Communications |language=en |volume=15 |issue=1 |page=5029 |doi=10.1038/s41467-024-49346-2 |pmid=38866733 |pmc=11169600 |issn=2041-1723|arxiv=2312.05244 |bibcode=2024NatCo..15.5029A }}</ref> The beam demonstrated the highest positron yield achieved so far in a laboratory setting. The experiment employed the 440 GeV proton beam, with <math>3\times 10^{11}</math> protons, from the [[Super Proton Synchrotron]], and irradiated a particle converter composed of [[carbon]] and [[tantalum]]. This yielded a total <math>1.5\times 10^{13}</math> electron-positron pairs via a [[particle shower]] process. The produced pair beams have a volume that fills multiple [[Debye length|Debye spheres]] and are thus able to sustain collective plasma oscillations.<ref name=":0" />

===Antiprotons, antineutrons, and antinuclei===
{{Main|Antiproton|Antineutron}}

The existence of the antiproton was experimentally confirmed in 1955 by [[University of California, Berkeley]] [[physicist]]s [[Emilio Segrè]] and [[Owen Chamberlain]], for which they were awarded the 1959 [[Nobel Prize in Physics]].<ref>{{cite web | url=http://nobelprize.org/nobel_prizes/physics/laureates/ | title=All Nobel Prizes in Physics | archive-url=https://web.archive.org/web/20100723052215/http://nobelprize.org/nobel_prizes/physics/laureates/ | archive-date=23 July 2010 | url-status=live}}</ref> An antiproton consists of two up antiquarks and one down antiquark ({{Subatomic particle|link=yes|Up antiquark}}{{Subatomic particle|link=yes|Up antiquark}}{{Subatomic particle|link=yes|Down antiquark}}). The properties of the antiproton that have been measured all match the corresponding properties of the proton, with the exception of the antiproton having opposite electric charge and magnetic moment from the proton. Shortly afterwards, in 1956, the antineutron was discovered in proton–proton collisions at the [[Bevatron]] ([[Lawrence Berkeley National Laboratory]]) by [[Bruce Cork]] and colleagues.<ref>{{cite web | url=http://bancroft.berkeley.edu/Exhibits/physics/extending02.html | title=Breaking Through: A Century of Physics at Berkeley, 1868–1968 | publisher=[[Regents of the University of California]] | date=2006 | access-date=18 November 2010 | archive-url=https://web.archive.org/web/20100709235643/http://bancroft.berkeley.edu/Exhibits/physics/extending02.html | archive-date=9 July 2010 | url-status=live}}</ref>

In addition to anti[[baryon]]s, anti-nuclei consisting of multiple bound antiprotons and antineutrons have been created. These are typically produced at energies far too high to form antimatter atoms (with bound positrons in place of electrons). In 1965, a group of researchers led by [[Antonino Zichichi]] reported production of nuclei of [[antideuterium]] at the Proton Synchrotron at [[CERN]].<ref>{{cite journal | bibcode=1965NCimS..39...10M | title=Experimental observation of antideuteron production | date=1965 | last1=Massam | first1=T. | last2=Muller | first2=Th. | last3=Righini | first3=B. | last4=Schneegans | first4=M. | last5=Zichichi | first5=A. | journal=Il Nuovo Cimento | volume=39 | issue=1 | pages=10–14 | doi=10.1007/BF02814251| s2cid=122952224 }}</ref> At roughly the same time, observations of antideuterium nuclei were reported by a group of American physicists at the Alternating Gradient Synchrotron at [[Brookhaven National Laboratory]].<ref>{{cite journal | bibcode=1965PhRvL..14.1003D | date=June 1965 | first1=D. E | last1=Dorfan | title=Observation of Antideuterons | last2=Eades | first2=J. | last3=Lederman | first3=L. M. | last4=Lee | first4=W. | last5=Ting | first5=C. C. | journal=Physical Review Letters | volume=14 | issue=24 | pages=1003–1006 | doi=10.1103/PhysRevLett.14.1003}}</ref>

===Antihydrogen atoms===
{{Main|Antihydrogen}}
<!-- Should antihelium be folded into this section? I haven't checked to see whether they'd created antihelium nuclei or true antihelium atoms with bound positrons. -->
{{Antimatter_facilities}}
In 1995, [[CERN]] announced that it had successfully brought into existence nine hot antihydrogen atoms by implementing the [[SLAC]]/[[Fermilab]] concept during the [[PS210 experiment]]. The experiment was performed using the [[Low Energy Antiproton Ring]] (LEAR), and was led by Walter Oelert and Mario Macri.<ref>{{Cite web
 |last=Gabrielse
 |first=Gerald
 |display-authors=etal
 |collaboration=ATRAP Collaboration
 |year=1996
 |title=The production and study of cold antihydrogen
 |url=https://cds.cern.ch/record/299823/files/B00006161.pdf
 |pages=1–21
 |publisher=CERN
 |id=No. SPSLC-I-211
 |access-date=22 August 2018
 |archive-date=25 March 2020
 |archive-url=https://web.archive.org/web/20200325005019/https://cds.cern.ch/record/299823/files/B00006161.pdf
 |url-status=live
 }}</ref> Fermilab soon confirmed the CERN findings by producing approximately 100 antihydrogen atoms at their facilities. The antihydrogen atoms created during PS210 and subsequent experiments (at both CERN and Fermilab) were extremely energetic and were not well suited to study. To resolve this hurdle, and to gain a better understanding of antihydrogen, two collaborations were formed in the late 1990s, namely, [[ATHENA]] and [[ATRAP]].

In 1999, CERN activated the [[Antiproton Decelerator]], a device capable of decelerating antiprotons from {{val|3.5|ul=GeV}} to {{val|5.3|u=MeV}}&nbsp;– still too "hot" to produce study-effective antihydrogen, but a huge leap forward. In late 2002 the ATHENA project announced that they had created the world's first "cold" antihydrogen.<ref>{{cite journal
 |last=Amoretti
 |first=M.
 |display-authors=etal
 |date=2002
 |title=Production and detection of cold antihydrogen atoms
 |url=https://cds.cern.ch/record/581488
 |journal=[[Nature (journal)|Nature]]
 |volume=419
 |issue=6906
 |pages=456–459
 |bibcode=2002Natur.419..456A
 |doi=10.1038/nature01096
 |pmid=12368849
 |s2cid=4315273
 |access-date=30 August 2017
 |archive-date=23 March 2020
 |archive-url=https://web.archive.org/web/20200323082118/https://cds.cern.ch/record/581488
 |url-status=live
 |doi-access=free
 }}</ref> The ATRAP project released similar results very shortly thereafter.<ref>{{cite journal
 |last=Gabrielse
 |first=G.
 |display-authors=etal
 |date=2002
 |title=Background-free observation of cold antihydrogen with field ionization analysis of its states
 |url=https://cds.cern.ch/record/977774
 |journal=[[Physical Review Letters]]
 |volume=89
 |issue=21
 |article-number=213401
 |bibcode=2002PhRvL..89u3401G
 |doi=10.1103/PhysRevLett.89.213401
 |pmid=12443407
 |access-date=30 August 2017
 |archive-date=23 March 2020
 |archive-url=https://web.archive.org/web/20200323082107/https://cds.cern.ch/record/977774
 |url-status=live
 }}</ref> The antiprotons used in these experiments were cooled by decelerating them with the Antiproton Decelerator, passing them through a thin sheet of foil, and finally capturing them in a [[Penning-Malmberg trap|Penning–Malmberg trap]].<ref>
{{cite journal
 |last1=Malmberg |first1=J. H.
 |last2=deGrassie |first2=J. S.
 |date=1975
 |title=Properties of a nonneutral plasma
 |journal=[[Physical Review Letters]]
 |volume=35 |issue=9 |pages=577–580
 |bibcode=1975PhRvL..35..577M
 |doi=10.1103/PhysRevLett.35.577
}}</ref> The overall cooling process is workable, but highly inefficient; approximately 25&nbsp;million antiprotons leave the Antiproton Decelerator and roughly 25,000 make it to the Penning–Malmberg trap, which is about {{sfrac|1|1000}} or 0.1% of the original amount.

The antiprotons are still hot when initially trapped. To cool them further, they are mixed into an electron plasma. The electrons in this plasma cool via cyclotron radiation, and then sympathetically cool the antiprotons via [[Coulomb potential|Coulomb]] collisions. Eventually, the electrons are removed by the application of short-duration electric fields, leaving the antiprotons with energies less than {{val|100|u=[[Electronvolt|meV]]}}.<ref>
{{cite journal
 |last=Gabrielse |first=G.
 |display-authors=etal
 |date=1989
 |title=Cooling and slowing of trapped antiprotons below 100 meV
 |journal=[[Physical Review Letters]]
 |volume=63 |issue=13 |pages=1360–1363
 |bibcode=1989PhRvL..63.1360G
 |doi=10.1103/PhysRevLett.63.1360
 |pmid=10040547
 }}</ref> While the antiprotons are being cooled in the first trap, a small cloud of positrons is captured from [[radioactive]] [[sodium]] in a Surko-style positron accumulator.<ref>
{{cite journal
 |last1=Surko |first1=C. M.
 |last2=Greaves |first2=R. G.
 |date=2004
 |title=Emerging science and technology of antimatter plasmas and trap-based beams
 |journal=[[Physics of Plasmas]]
 |volume=11 |issue=5 |page=2333
 |bibcode=2004PhPl...11.2333S
 |doi=10.1063/1.1651487
}}</ref> This cloud is then recaptured in a second trap near the antiprotons. Manipulations of the trap electrodes then tip the antiprotons into the positron plasma, where some combine with antiprotons to form antihydrogen. This neutral antihydrogen is unaffected by the electric and magnetic fields used to trap the charged positrons and antiprotons, and within a few microseconds the antihydrogen hits the trap walls, where it annihilates. Some hundreds of millions of antihydrogen atoms have been made in this fashion.

In 2005, ATHENA disbanded and some of the former members (along with others) formed the [[ALPHA Collaboration]], which is also based at CERN. The ultimate goal of this endeavour is to test [[CPT symmetry]] through comparison of the [[atomic spectra]] of [[hydrogen]] and antihydrogen (see [[hydrogen spectral series]]).<ref>
{{cite journal
 |last=Madsen |first=N.
 |date=2010
 |title=Cold antihydrogen: a new frontier in fundamental physics
 |journal=[[Philosophical Transactions of the Royal Society A]]
 |volume=368 |issue=1924 |pages=3671–82
 |bibcode=2010RSPTA.368.3671M
 |doi=10.1098/rsta.2010.0026
 |pmid=20603376
|doi-access=free
 }}</ref>

Most of the sought-after high-precision tests of the properties of antihydrogen could only be performed if the antihydrogen were trapped, that is, held in place for a relatively long time. While antihydrogen atoms are electrically neutral, the [[Spin (physics)|spins]] of their component particles produce a [[magnetic moment]]. These magnetic moments can interact with an inhomogeneous magnetic field; some of the antihydrogen atoms can be attracted to a magnetic minimum. Such a minimum can be created by a combination of mirror and multipole fields.<ref>
{{cite journal
 |last1=Pritchard |first1=D. E.
 |last2=Heinz |first2=T.
 |last3=Shen |first3=Y.
 |date=1983
 |title=Cooling neutral atoms in a magnetic trap for precision spectroscopy
 |journal=[[Physical Review Letters]]
 |volume=51 |issue=21 |pages=1983–1986
 |bibcode=1983PhRvL..51.1983T
 |doi=10.1103/PhysRevLett.51.1983
}}</ref> Antihydrogen can be trapped in such a magnetic minimum (minimum-B) trap; in November 2010, the ALPHA collaboration announced that they had so trapped 38 antihydrogen atoms for about a sixth of a second.<ref>
{{cite journal
 |last=Andresen |display-authors=etal
 |date=2010
 |title=Trapped antihydrogen
 |journal=[[Nature (journal)|Nature]]
 |volume=468 |issue=7324 |pages=673–676
 |bibcode=2010Natur.468..673A
 |doi=10.1038/nature09610
 |pmid=21085118
|s2cid=2209534
 }}</ref><ref>
{{cite web
 |title=Antimatter atoms produced and trapped at CERN
 |url=http://public.web.cern.ch/press/pressreleases/Releases2010/PR22.10E.html
 |publisher=[[CERN]]
 |access-date=20 January 2011
 |date=17 November 2010
 |archive-url=https://web.archive.org/web/20110123232026/http://public.web.cern.ch/press/pressreleases/Releases2010/PR22.10E.html
 |archive-date=23 January 2011
 }}</ref> This was the first time that neutral antimatter had been trapped.

On 26 April 2011, ALPHA announced that they had trapped 309 antihydrogen atoms, some for as long as 1,000 seconds (about 17 minutes). This was longer than neutral antimatter had ever been trapped before.<ref>{{cite journal
 |author=ALPHA Collaboration
 |date=2011
 |title=Confinement of antihydrogen for 1,000 seconds
 |url=https://cds.cern.ch/record/1347171
 |journal=[[Nature Physics]]
 |volume=7
 |issue=7
 |pages=558–564
 |arxiv=1104.4982
 |bibcode=2011NatPh...7..558A
 |doi=10.1038/nphys2025
 |s2cid=17151882
 |access-date=22 August 2018
 |archive-date=23 March 2020
 |archive-url=https://web.archive.org/web/20200323082111/https://cds.cern.ch/record/1347171
 |url-status=live
 }}</ref> ALPHA has used these trapped atoms to initiate research into the spectral properties of antihydrogen.<ref>{{Cite journal
 |last1=Amole
 |first1=C.
 |display-authors=etal
 |date=2012
 |title=Resonant quantum transitions in trapped antihydrogen atoms
 |url=https://cds.cern.ch/record/1430040/files/Nature_pre.pdf
 |journal=Nature
 |volume=483
 |issue=7390
 |pages=439–443
 |pmid=22398451
 |bibcode=2012Natur.483..439A
 |hdl=11568/757495
 |doi=10.1038/nature10942
 |s2cid=2321196
 |access-date=25 October 2017
 |archive-date=23 March 2020
 |archive-url=https://web.archive.org/web/20200323082130/https://cds.cern.ch/record/1430040/files/Nature_pre.pdf
 |url-status=live
 }}</ref>

In 2016, a new antiproton decelerator and cooler called ELENA (extra low energy antiproton decelerator) was built. It takes the antiprotons from the antiproton decelerator and cools them to 90&nbsp;keV, which is "cold" enough to study. This machine works by using high energy and accelerating the particles within the chamber. More than one hundred antiprotons can be captured per second, a huge improvement, but it would still take several thousand years to make a [[nanogram]] of antimatter.

The biggest limiting factor in the large-scale production of antimatter is the availability of antiprotons. Recent data released by CERN states that, when fully operational, their facilities are capable of producing ten million antiprotons per minute.<ref>{{cite journal
 |last=Madsen
 |first=N.
 |date=2010
 |title=Cold antihydrogen: a new frontier in fundamental physics
 |journal=[[Philosophical Transactions of the Royal Society A]]
 |volume=368
 |issue=1924
 |pages=3671–82
 |bibcode=2010RSPTA.368.3671M
 |doi=10.1098/rsta.2010.0026
 |pmid=20603376
 |url=https://zenodo.org/record/889475
 |doi-access=free
 |access-date=9 September 2019
 |archive-date=29 March 2020
 |archive-url=https://web.archive.org/web/20200329132655/https://zenodo.org/record/889475
 |url-status=live
 }}</ref> Assuming a 100% conversion of antiprotons to antihydrogen, it would take 100&nbsp;billion years to produce 1&nbsp;gram or 1 [[Mole (unit)|mole]] of antihydrogen (approximately {{val|6.02|e=23}} atoms of antihydrogen). However, CERN only produces 1% of the antimatter Fermilab does, and neither are designed to produce antimatter. According to Gerald Jackson, using technology already in use today we are capable of producing and capturing 20 grams of antimatter particles per year at a yearly cost of 670 million dollars per facility.<ref>{{cite journal |last1=Jackson |first1=Gerald |date=December 2022 |title=Antimatter-Based Propulsion for Exoplanet Exploration |url=https://www.ans.org/pubs/journals/nt/article-52262/ |journal=Nuclear Technology |volume=208 |issue=1 |pages=S107–S112|doi=10.1080/00295450.2021.1997057 |bibcode=2022NucTe.208S.107J |doi-access=free }}</ref><ref>{{Cite journal |last=Jackson |first=Gerald P. |date=2022-08-01 |title=Deceleration of Exoplanet Missions Utilizing Scarce Antimatter |url=https://www.sciencedirect.com/science/article/pii/S0094576522001163 |journal=Acta Astronautica |volume=197 |pages=380–386 |doi=10.1016/j.actaastro.2022.03.018 |bibcode=2022AcAau.197..380J |issn=0094-5765|url-access=subscription }}</ref>

===Antihelium===
Antihelium-3 nuclei ({{SimpleNuclide|anti=yes|helium|3}}, i.e. two antiprotons and one antineutron) were first observed in the 1970s in proton–nucleus collision experiments at the Institute for High Energy Physics by Y. Prockoshkin's group (Protvino near Moscow, USSR)<ref>
{{cite journal
 |first=Yu. M. |last=Antipov
 |display-authors=etal
 |title=Observation of {{overline|He³}}
 |language=ru
 |journal=Journal of Nuclear Physics
 |volume=12 |issue=2
 |orig-date=Received 30 March 1970
 |year=1970
 |pages=311–322
 |issn=0044-0027
}}<br/>
{{cite journal
 |first1=Yu. M. |last1=Antipov
 |first2=S. P.  |last2=Denisov
 |first3=S. V.  |last3=Donskov
 |first4=Yu. P. |last4=Gorin
 |first5=V. A.  |last5=Kachanov
 |first6=V. P.  |last6=Khromov
 |first7=V. M.  |last7=Kutyin
 |first8=L. G.  |last8=Landsberg
 |first9=V. G.  |last9=Lapshin
 |first10=A. A. |last10=Lebedev
 |first11=A. G. |last11=Morozov
 |first12=A. I. |last12=Petrukhin
 |first13=Yu. D.|last13=Prokoshkin
 |first14=E. A. |last14=Razuvaev
 |first15=V. I. |last15=Rykalin
 |first16=R. S. |last16=Shovalov
 |first17=V. I. |last17=Soljanick
 |first18=D. A. |last18=Stoyanova
 |first19=N. K. |last19=Vishnevsky
 |first20=F. A. |last20=Yetch
 |first21=A. M. |last21=Zajtzev
 |first22=G. D. |last22=Zhilchenkova
 |display-authors=1
 |title=Observation of antihelium-3
 |journal=Nuclear Physics B
 |volume=31 |issue=2
 |orig-date=Received 11 December 1970
 |year=1971
 |pages=235–252
 |issn=0550-3213
 |doi=10.1016/0550-3213(71)90228-8
 |bibcode=1971NuPhB..31..235A
 |url=https://dx.doi.org/10.1016/0550-3213%2871%2990228-8
 |access-date=29 October 2025
}}</ref> and later created in nucleus–nucleus collision experiments.<ref>
{{cite journal
 |last=Arsenescu |first=R.
 |display-authors=etal
 |date=2003
 |title=Antihelium-3 production in lead–lead collisions at 158&nbsp;''A''&nbsp;GeV/''c''
 |journal=[[New Journal of Physics]]
 |volume=5 |issue=1 |page=1
 |bibcode=2003NJPh....5....1A
 |doi=10.1088/1367-2630/5/1/301
|doi-access=free
 }}</ref> Nucleus–nucleus collisions produce antinuclei through the coalescence of antiprotons and antineutrons created in these reactions. In 2011, the [[STAR detector]] reported the observation of artificially created antihelium-4 nuclei (anti-alpha particles) ({{SimpleNuclide|anti=yes|helium|4}}) from such collisions.<ref>
{{cite journal
 |last=Agakishiev |first=H.
 |display-authors=etal
 |date=2011
 |title=Observation of the antimatter helium-4 nucleus
 |journal=Nature
 |volume=473 |issue=7347 |pages=353–356
 |arxiv=1103.3312
 |doi=10.1038/nature10079
 |bibcode=2011Natur.473..353S
 |pmid=21516103
|s2cid=118484566
 }}</ref>

The [[Alpha Magnetic Spectrometer]] on the [[International Space Station]] has, as of 2021, recorded eight events that seem to indicate the detection of antihelium-3.<ref>{{cite journal |last1=Leah Crane |title=Antimatter stars may lurk in the solar system's neighbourhood |journal=New Scientist |date=May 1, 2021 |url=https://www.newscientist.com/article/2275563-antimatter-stars-may-lurk-in-the-solar-systems-neighbourhood/ |access-date=1 May 2021 |archive-date=1 May 2021 |archive-url=https://web.archive.org/web/20210501150008/https://www.newscientist.com/article/2275563-antimatter-stars-may-lurk-in-the-solar-systems-neighbourhood/ |url-status=live }}</ref><ref>{{cite journal |first=Joshua |last=Sokol |title=Giant space magnet may have trapped antihelium, raising idea of lingering pools of antimatter in the cosmos |journal=Science |date=Apr 19, 2017 |doi=10.1126/science.aal1067 |url=https://www.science.org/content/article/giant-space-magnet-may-have-trapped-antihelium-raising-idea-lingering-pools-antimatter |access-date=1 May 2021 |archive-date=1 May 2021 |archive-url=https://web.archive.org/web/20210501145420/https://www.sciencemag.org/news/2017/04/giant-space-magnet-may-have-trapped-antihelium-raising-idea-lingering-pools-antimatter |url-status=live |url-access=subscription }}</ref>

===Preservation===
<!--===Antimatter trap===!-->

Antimatter cannot be stored in a container made of ordinary matter because antimatter reacts with any matter it touches, annihilating itself and an equal amount of the container. Antimatter in the form of [[charged particle]]s can be contained by a combination of [[electric field|electric]] and [[magnetic field|magnetic]] fields, in a device called a [[Penning trap]]. This device cannot, however, contain antimatter that consists of uncharged particles, for which [[atomic trap]]s are used. In particular, such a trap may use the [[dipole]] moment ([[Electric dipole moment|electric]] or [[Magnetic moment|magnetic]]) of the trapped particles. At high [[vacuum]], the matter or antimatter particles can be trapped and cooled with slightly off-resonant laser radiation using a [[magneto-optical trap]] or [[Magnetic trap (atoms)|magnetic trap]]. Small particles can also be suspended with [[optical tweezers]], using a highly focused laser beam.<ref>
{{cite journal
 |last1=Blaum |first1=K.
 |last2=Raizen |first2=M. G.
 |last3=Quint |first3=W.
 |year=2014
 |title=An experimental test of the weak equivalence principle for antihydrogen at the future FLAIR facility
 |journal=[[International Journal of Modern Physics: Conference Series]]
 |volume=30 |page=1460264
 |bibcode=2014IJMPS..3060264B
 |doi=10.1142/S2010194514602646
 |hdl=11858/00-001M-0000-001A-152D-1
|hdl-access=free
 }}</ref>

In 2011, [[CERN]] scientists were able to preserve antihydrogen for approximately 17 minutes.<ref>{{cite news|date=9 June 2011|title=Antimatter of Fact|url=https://www.economist.com/science-and-technology/2011/06/09/antimatter-of-fact|newspaper=The Economist|url-status=live|archive-url=https://web.archive.org/web/20140217051839/http://www.economist.com/node/18802932|archive-date=17 February 2014}}</ref> The record for storing antiparticles is currently held by the TRAP experiment at CERN: antiprotons were kept in a Penning trap for 405 days.<ref>{{Cite journal|title=Improved limit on the directly measured antiproton lifetime|journal=New Journal of Physics|year=2017|doi=10.1088/1367-2630/aa7e73|last1=Sellner|first1=S.|last2=Besirli|first2=M.|last3=Bohman|first3=M.|last4=Borchert|first4=M. J.|last5=Harrington|first5=J.|last6=Higuchi|first6=T.|last7=Mooser|first7=A.|last8=Nagahama|first8=H.|last9=Schneider|first9=G.|last10=Smorra|first10=C.|last11=Tanaka|first11=T.|last12=Blaum|first12=K.|last13=Matsuda|first13=Y.|last14=Ospelkaus|first14=C.|last15=Quint|first15=W.|last16=Walz|first16=J.|last17=Yamazaki|first17=Y.|last18=Ulmer|first18=S.|volume=19|issue=8|page=083023|bibcode=2017NJPh...19h3023S|doi-access=free}}</ref> A proposal was made in 2018 to develop containment technology advanced enough to contain a billion anti-protons in a portable device to be driven to another lab for further experimentation.<ref>
{{cite journal|last1=Gibney |first1=E.|year=2018|title=Physicists plan antimatter's first outing – in a van|journal=[[Nature (journal)|Nature]]|volume=554 |issue=7693 |pages=412–413|bibcode=2018Natur.554..412G|doi=10.1038/d41586-018-02221-9|pmid=29469122|s2cid=4448531|doi-access=free}}</ref>

===Cost===
Scientists claim that antimatter is the costliest material to make.<ref name="NASA1999"/> In 2006, Gerald Smith estimated $250&nbsp;million could produce 10 milligrams of positrons<ref>
{{cite web
 |last=Steigerwald |first=B.
 |date=14 March 2006
 |title=New and Improved Antimatter Spaceship for Mars Missions
 |url=http://www.nasa.gov/exploration/home/antimatter_spaceship.html
 |publisher=[[NASA]]
 |quote="A rough estimate to produce the 10 milligrams of positrons needed for a human Mars mission is about 250 million dollars using technology that is currently under development," said Smith.
 |access-date=11 June 2010
 |archive-url=https://web.archive.org/web/20110806181954/http://www.nasa.gov/exploration/home/antimatter_spaceship.html
 |archive-date=6 August 2011
 |url-status=live
}}</ref> (equivalent to $25&nbsp;billion per gram); in 1999, NASA gave a figure of $62.5&nbsp;trillion per gram of antihydrogen.<ref name="NASA1999">
{{cite web
 |date=12 April 1999
 |title=Reaching for the stars: Scientists examine using antimatter and fusion to propel future spacecraft
 |url=https://science.nasa.gov/science-news/science-at-nasa/1999/prop12apr99_1
 |publisher=[[NASA]]
 |quote=Antimatter is the most expensive substance on Earth
 |access-date=11 June 2010
 |archive-url=https://web.archive.org/web/20100612110153/http://science.nasa.gov/science-news/science-at-nasa/1999/prop12apr99_1/
 |archive-date=12 June 2010
 |url-status=live
}}</ref> This is because production is difficult (only very few antiprotons are produced in reactions in particle accelerators) and because there is higher demand for other uses of [[particle accelerator]]s. According to CERN, it has cost a few hundred million [[Swiss franc]]s to produce about 1&nbsp;billionth of a gram (the amount used so far for particle/antiparticle collisions).<ref>
{{cite web
 |date=2001
 |title=Antimatter Questions & Answers
 |url=http://livefromcern.web.cern.ch/livefromcern/antimatter/FAQ1.html
 |archive-url=https://archive.today/20080421220420/http://livefromcern.web.cern.ch/livefromcern/antimatter/FAQ1.html
 |archive-date=2008-04-21
 |publisher=[[CERN]]
 |access-date=24 May 2008
 }}</ref> In comparison, to produce the first atomic weapon, the cost of the [[Manhattan Project]] was estimated at $23&nbsp;billion with inflation during 2007.<ref>
{{cite web
 |title=Manhattan Project: CTBTO Preparatory Commission
 |url=http://www.ctbto.org/nuclear-testing/history-of-nuclear-testing/manhattan-project/
 |archive-url=https://web.archive.org/web/20141222033224/http://www.ctbto.org/nuclear-testing/history-of-nuclear-testing/manhattan-project/
 |archive-date=22 December 2014
 |url-status=live
}}</ref>

Several studies funded by [[NASA Innovative Advanced Concepts]] are exploring whether it might be possible to use magnetic scoops to collect the antimatter that occurs naturally in the [[Van Allen radiation belt|Van Allen belt]] of the Earth, and ultimately the belts of gas giants like [[Jupiter]], ideally at a lower cost per gram.<ref>
{{cite web
 |last=Bickford |first=J.
 |title=Extraction of Antiparticles Concentrated in Planetary Magnetic Fields
 |url=https://www.centauri-dreams.org/wp-content/Bickford_Phase_II.pdf
 |publisher=[[NASA]] and Draper Laboratory
 | date= Aug 2007
|archive-url=https://web.archive.org/web/20080723210113/http://www.niac.usra.edu/files/studies/abstracts/1071Bickford.pdf
 |archive-date=23 July 2008
 |url-status=live
 }}</ref>

==Uses==

===Medical===
[[File:16slicePETCT.jpg|thumb|A PET/CT system]]
Matter–antimatter reactions have practical applications in medical imaging, such as [[positron emission tomography]] (PET). In positive [[beta decay]], a [[nuclide]] loses surplus positive charge by emitting a positron (in the same event, a proton becomes a neutron, and a [[neutrino]] is also emitted). Nuclides with surplus positive charge are easily made in a [[cyclotron]] and are widely generated for medical use. Antiprotons have also been shown within laboratory experiments to have the potential to treat certain cancers, in a similar method currently used for ion (proton) therapy.<ref>
{{cite journal
 |title=Antiproton portable traps and medical applications
 |journal=Hyperfine Interactions
 |volume=109
 |issue=1–4
 |page=155
 |url=http://www.engr.psu.edu/antimatter/Papers/pbar_med.pdf
 |archive-url=https://web.archive.org/web/20110822150631/http://www.engr.psu.edu/antimatter/Papers/pbar_med.pdf
 |archive-date=22 August 2011
 |bibcode=1997HyInt.109..155L
 |last1=Lewis
 |first1=R. A.
 |last2=Smith
 |first2=G. A.
 |last3=Howe
 |first3=S. D.
 |year=1997
 |doi=10.1023/A:1012653416870
 |s2cid=120402661
 }}</ref>

===Fuel===<!-- This section is linked from [[Deuterium]] -->
Isolated and stored antimatter could be used as a [[fuel]] for [[interplanetary spaceflight|interplanetary]] or [[interstellar travel]]<ref>{{cite book
 |last=Schmidt |first=G. R.
 |title=35th Joint Propulsion Conference and Exhibit
 |date=1999
 |chapter=Antimatter Production for Near-Term Propulsion Applications
 |publisher=American Institute of Aeronautics and Astronautics
 |doi=10.2514/6.1999-2691
}}</ref> as part of an [[antimatter-catalyzed nuclear pulse propulsion]] or another [[antimatter rocket]]. Since the energy density of antimatter is higher than that of conventional fuels, an antimatter-fueled spacecraft would have a higher [[thrust-to-weight ratio]] than a conventional spacecraft.

If matter–antimatter collisions resulted only in [[photon]] emission, the entire [[rest mass]] of the particles would be converted to [[kinetic energy]]. The [[energy density|energy per unit mass]] ({{val|9|e=16|u=J/kg}}) is about 10 [[order of magnitude|orders of magnitude]] greater than [[chemical energy|chemical energies]],<ref>(compared to the [[heat of formation|formation]] of water at {{val|1.56|e=7|u=J/kg}}, for example)</ref> and about 3 orders of magnitude greater than the [[nuclear potential energy]] that can be liberated, today, using [[nuclear fission]] (about {{val|200|u=MeV}} per fission reaction<ref>{{cite web
 |last=Sowerby
 |first=M. G.
 |title=§4.7 Nuclear fission and fusion, and neutron interactions
 |url=http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1.html
 |work=Kaye & Laby: Table of Physical & Chemical Constants
 |publisher=[[National Physical Laboratory (United Kingdom)|National Physical Laboratory]]
 |access-date=18 June 2010
 |archive-url=https://web.archive.org/web/20100305114800/http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1.html
 |archive-date=5 March 2010
 }}</ref> or {{val|8|e=13|u=J/kg}}), and about 2 orders of magnitude greater than the best possible results expected from [[nuclear fusion|fusion]] (about {{val|6.3|e=14|u=J/kg}} for the [[proton–proton chain]]). The reaction of {{val|1|ul=kg}} of antimatter with {{val|1|u=kg}} of matter would produce {{val|1.8|e=17|ul=J}} (180 [[Orders of magnitude (energy)#1012 to 1017 J|petajoules]]) of energy (by the [[mass–energy equivalence]] formula, {{nowrap|1=''E''=''mc''<sup>2</sup>}}), or the rough equivalent of 43 megatons of TNT – slightly less than the yield of the 27,000&nbsp;kg [[Tsar Bomba]], the largest [[thermonuclear weapon]] ever detonated.

Not all of that energy can be utilized by any realistic propulsion technology because of the nature of the annihilation products. While electron–positron reactions result in gamma ray photons, these are difficult to direct and use for thrust. In reactions between protons and antiprotons, their energy is converted largely into relativistic neutral and charged [[pion]]s. The [[Pion#Neutral pion decays|neutral pions]] decay almost immediately (with a lifetime of 85 [[attoseconds]]) into high-energy photons, but the [[Pion#Charged pion decays|charged pions]] decay more slowly (with a lifetime of 26 nanoseconds) and can be [[Antimatter rocket#Direct use of reaction products|deflected magnetically to produce thrust]].

Charged pions ultimately decay into a combination of [[neutrino]]s (carrying about 22% of the energy of the charged pions) and unstable charged [[muon]]s (carrying about 78% of the charged pion energy), with the muons then decaying into a combination of electrons, positrons and neutrinos (cf. [[muon decay]]; the neutrinos from this decay carry about 2/3 of the energy of the muons, meaning that from the original charged pions, the total fraction of their energy converted to neutrinos by one route or another would be about {{nowrap|1=0.22 + (2/3)⋅0.78 = 0.74}}).<ref>
{{cite web
 |last=Borowski |first=S. K.
 |date=1987
 |title=Comparison of Fusion/Antiproton Propulsion systems
 |url=http://gltrs.grc.nasa.gov/reports/1996/TM-107030.pdf
 |pages=5–6 (pp. 6–7 of pdf)
 |work=NASA Technical Memorandum 107030
 |publisher=[[NASA]]
 |id=AIAA–87–1814
 |access-date=24 May 2008
 |archive-url=https://web.archive.org/web/20080528030524/http://gltrs.grc.nasa.gov/reports/1996/TM-107030.pdf
 |archive-date=28 May 2008
 }}</ref><!--

For more regular (earthly) applications (for example, regular transport, use in portable generators, and the powering of cities) artificially created antimatter is not a suitable energy carrier, despite its high energy density, because the process of creating antimatter is extremely inefficient. According to CERN, only one part in ten billion ({{val|e=-10}}) of the energy invested in the production of antimatter particles can be subsequently retrieved.<ref>
{{cite web
 |year=2004 [2008]
 |title=Angels and Demons: Inefficiency of Antimatter
 |url=http://public.web.cern.ch/public/en/Spotlight/SpotlightAandD-en.html
 |publisher=[[CERN]]
 |access-date=18 November 2010
 |archive-url=https://web.archive.org/web/20101116160609/http://public.web.cern.ch/public/en/Spotlight/SpotlightAandD-en.html
 |archive-date=16 November 2010
}}</ref>

Antimatter production is currently very limited, but has been growing at a nearly [[geometric progression|geometric rate]] since the observation of the first antiproton in 1955 by Segrè and Chamberlain.<ref>
{{cite web
 |year=2006
 |title=1955: Emilio Segrè, Owen Chamberlain, and the matter of antimatter
 |url=http://sciencematters.berkeley.edu/archives/volume1/issue1/legacy.php
 |publisher=[[Regents of the University of California]]
 |access-date=18 November 2010
 |archive-url=https://web.archive.org/web/20100610093620/http://sciencematters.berkeley.edu/archives/volume1/issue1/legacy.php
 |archive-date=10 June 2010
}}</ref> The current antimatter production rate is between 1 and 10 nanograms per year, and this is expected to increase to between 3 and 30 nanograms per year by 2015 or 2020 with new superconducting linear accelerator facilities at CERN and [[Fermilab]].

Some researchers{{Who|date=May 2012}} claim that with current technology, it is possible to obtain antimatter for [[United States dollar|US$]]25 million per gram by optimizing the collision and collection parameters (given current electricity generation costs).{{Citation needed|date=May 2012}}
Many experts{{Who|date=March 2011}}, however, dispute these claims as being far too optimistic by many orders of magnitude. They point out that, in 2004, the annual production of antiprotons at [[CERN]] was several picograms at a cost of $20 million. This means that to produce 1&nbsp;gram of antimatter, [[CERN]] would need to spend 100 quadrillion ({{val|e=17}}) dollars and run the antimatter factory for 100 billion years.

Antimatter production costs, in mass production, are almost linearly tied to electricity costs, so economical pure-antimatter thrust applications are unlikely to come online unless a very cheap power source is found.

Storage is another problem, as antiprotons are negatively charged and repel each other, so that they cannot be concentrated in a small volume (cf. [[space charge]]). [[Plasma oscillation]]s in the charged cloud of antiprotons can cause instabilities that drive antiprotons out of the storage trap. For these reasons, to date, only a few million antiprotons have been stored simultaneously in a magnetic trap, which corresponds to much less than a femtogram. Antihydrogen atoms or molecules are of neutral charge, they are not as ionically unstable as antiprotons. The drawback is that cold antihydrogen is far more complex to produce than mere antiprotons.

One researcher from the CERN laboratories, which produces antimatter regularly, said:
{{quote|If we could assemble all of the antimatter we've ever made at CERN and annihilate it with matter, we would have enough energy to light a single electric light bulb for a few minutes.<ref>
{{cite web
 |year=2004 [2008]
 |title=Angels and Demons: Do antimatter atoms exist?
 |url=http://public.web.cern.ch/public/en/Spotlight/SpotlightAandD-en.html
 |publisher=[[CERN]]
 |access-date=2010-11-18
 |archive-url=https://web.archive.org/web/20101116160609/http://public.web.cern.ch/public/en/Spotlight/SpotlightAandD-en.html
 |archive-date=2010-11-16
}}</ref>}}
--->

===Weapons===
{{Main|Antimatter weapon}}

Antimatter has been considered as a trigger mechanism for nuclear weapons.<ref>
{{cite web
 |url=http://cui.unige.ch/isi/sscr/phys/anti-BPP-3.html
 |title=Antimatter weapons
 |archive-url=https://web.archive.org/web/20130424174413/http://cui.unige.ch/isi/sscr/phys/anti-BPP-3.html
 |archive-date=24 April 2013
 |url-status=live
}}</ref> A major obstacle is the difficulty of producing antimatter in large enough quantities, and there is no evidence that it will ever be feasible.<ref>
{{Cite book
 |last1=Gsponer |first1=Andre
 |last2=Hurni |first2=Jean-Pierre
 |year=1987
 |chapter=The physics of antimatter induced fusion and thermonuclear explosions
 |editor1-last=Velarde |editor1-first=G.
 |editor2-last=Minguez |editor2-first=E.
 |title=Proceedings of the International Conference on Emerging Nuclear Energy Systems, Madrid, June/July, 1986
 |volume=4 |issue=30 |pages=66–169
 |publisher=[[World Scientific]]
 |arxiv=physics/0507114
 |bibcode=2005physics...7114G
}}</ref> Nonetheless, the [[United States Air Force|U.S. Air Force]] funded studies of the physics of antimatter in the [[Cold War]], and began considering its possible use in weapons, not just as a trigger, but as the explosive itself.<ref>
{{cite news
 |url=http://sfgate.com/cgi-bin/article.cgi?file=/c/a/2004/10/04/MNGM393GPK1.DTL
 |title=Air Force pursuing antimatter weapons / Program was touted publicly, then came official gag order
 |newspaper=Sfgate
 |date=4 October 2004
 |archive-url=https://web.archive.org/web/20120609101650/http://www.sfgate.com/cgi-bin/article.cgi?file=%2Fc%2Fa%2F2004%2F10%2F04%2FMNGM393GPK1.DTL
 |archive-date=9 June 2012
 |url-status=live
|last1=Davidson
 |first1=Keay
 }}</ref>

==See also==
{{Portal|Physics}}
* {{Annotated link|Alfvén–Klein cosmology}}
* [[Antihypernuclei]] – Antimatter hypernucleus
* {{Annotated link|Antimatter comet}}
* {{Annotated link|Di-positronium}}
* {{Annotated link|Gravitational interaction of antimatter}}
* {{Annotated link|Positronium hydride}}

==References==
{{Reflist|2}}

==Further reading==
* {{Cite book |last=Fraser |first=G. |title=Antimatter: The Ultimate Mirror |date=2000 |publisher=[[Cambridge University Press]] |isbn=978-0-521-65252-0 |location=Cambridge ; New York}}
* {{Cite conference |last1=Schmidt |first1=G.R |last2=Gerrish |first2=H.P. |last3=Martin |first3=J.J. |last4=Smith |first4=G.A. |last5=Meyer |first5=K.J. |date=22 August 2012 |title=Antimatter Production for Near-term Propulsion Applications |url=http://www.engr.psu.edu/antimatter/papers/nasa_anti.pdf |conference=35th Joint Propulsion Conference and Exhibit |publisher=[[American Institute of Aeronautics and Astronautics]] |doi=10.2514/6.1999-2691 |archive-url=https://web.archive.org/web/20070306065325/http://www.engr.psu.edu/antimatter/Papers/NASA_anti.pdf |archive-date=6 March 2007 }}
* {{Cite journal |last=Taylor |first=Allen |date=June 2012 |title=Angels and Demons |url=http://public.web.cern.ch/public/en/Spotlight/SpotlightAandD-en.html |journal=[[New Scientist]] |publisher=[[CERN]] |volume=214 |issue=2871 |page=31 |bibcode=2012NewSc.214R..31T |doi=10.1016/S0262-4079(12)61690-X |archive-url=https://web.archive.org/web/20140327204326/http://public.web.cern.ch/public/en/Spotlight/SpotlightAandD-en.html |archive-date=27 March 2014}} FAQ from CERN with information about antimatter aimed at the general reader, posted in response to antimatter's fictional portrayal in ''[[Angels & Demons]]''.

==External links==
{{Wikiquote}}
{{Commons category|Antimatter}}
* {{In Our Time|Antimatter|b00808w8|Antimatter}}
* [http://www.vega.org.uk/video/programme/14 Freeview Video 'Antimatter' by the Vega Science Trust and the BBC/OU]
* [https://web.archive.org/web/20000620014355/http://livefromcern.web.cern.ch/livefromcern/antimatter/webcast/AM-webcast06.html CERN Webcasts (RealPlayer required)]
* [https://web.archive.org/web/20051028075601/http://www.positron.edu.au/faq.html What is Antimatter?] (from the Frequently Asked Questions at the Center for Antimatter–Matter Studies)
* [https://web.archive.org/web/20140503090147/http://www2.slac.stanford.edu/tip/special/cp.htm What is direct CP-violation?]
* [http://www.exploratorium.edu/origins/cern/tools/animation.html Animated illustration of antihydrogen production at CERN] from the [[Exploratorium]].
* [https://www.nytimes.com/2024/08/30/science/astrophysics-dune-neutrinos.html "Mining for Neutrinos"], costly experiment to study neutrinos & anti-neutrinos. [[New York Times]] science article, updated Sept. 2, 2024

{{States of matter}}
{{Dark matter}}
{{Authority control}}

[[Category:Antimatter| ]]
[[Category:Quantum field theory]]
[[Category:Fictional power sources]]
[[Category:Articles containing video clips]]