Editing Antimatter (section)

===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 |page=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
 |pages=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 |pages=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
 }}</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|author=Joshua 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}}</ref>