Editing Cosmic ray (section)

====Primary cosmic ray antimatter====
{{see also|Alpha Magnetic Spectrometer}}
Satellite experiments have found evidence of positrons and a few antiprotons in primary cosmic rays, amounting to less than 1% of the particles in primary cosmic rays. These do not appear to be the products of large amounts of antimatter from the Big Bang, or indeed complex antimatter in the universe. Rather, they appear to consist of only these two elementary particles, newly made in energetic processes.

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. 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|first1=L.|last1=Accardo|display-authors=etal|collaboration=AMS Collaboration|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|journal=Physical Review Letters|date=18 September 2014|volume=113|issue=12|page=121101|doi=10.1103/PhysRevLett.113.121101|pmid=25279616|url=http://ams.nasa.gov/Documents/AMS_Publications/PhysRevLett.113.121101.pdf |archive-url=https://web.archive.org/web/20141017131844/http://ams.nasa.gov/Documents/AMS_Publications/PhysRevLett.113.121101.pdf |archive-date=2014-10-17 |url-status=live|bibcode=2014PhRvL.113l1101A|doi-access=free}}</ref><ref>{{Cite journal|last1=Schirber|first1=Michael|year=2014|title=Synopsis: More dark matter hints from cosmic rays?|journal=Physical Review Letters|volume=113|issue=12|page=121102|doi=10.1103/PhysRevLett.113.121102|pmid=25279617|arxiv=1701.07305|bibcode=2014PhRvL.113l1102A|url=https://cds.cern.ch/record/1756487|hdl=1721.1/90426|s2cid=2585508}}</ref> A new measurement of positron fraction up to 500 GeV was reported, showing that positron fraction peaks at a maximum of about 16% of total electron+positron events, around an energy of {{nowrap|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&nbsp;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 |archive-url=https://web.archive.org/web/20140923222913/http://ams.nasa.gov/Documents/AMS_Publications/ams_new_results_-_18.09.2014.pdf |archive-date=2014-09-23 |url-status=live|website=AMS-02 at NASA|access-date=21 September 2014}}</ref> These results on interpretation have been suggested to be due to positron production in annihilation events of massive [[dark matter]] particles.<ref>{{Cite journal|last1=Aguilar|first1=M.|last2=Alberti|first2=G.|last3=Alpat|first3=B.|last4=Alvino|first4=A.|last5=Ambrosi|first5=G.|last6=Andeen|first6=K.|last7=Anderhub|first7=H.|last8=Arruda|first8=L.|last9=Azzarello|first9=P.|last10=Bachlechner|first10=A.|last11=Barao|first11=F.|last12=Baret|first12=B.|last13=Barrau|first13=A.|last14=Barrin|first14=L.|last15=Bartoloni|first15=A.|last16=Basara|first16=L.|last17=Basili|first17=A.|last18=Batalha|first18=L.|last19=Bates|first19=J.|last20=Battiston|first20=R.|last21=Bazo|first21=J.|last22=Becker|first22=R.|last23=Becker|first23=U.|last24=Behlmann|first24=M.|last25=Beischer|first25=B.|last26=Berdugo|first26=J.|last27=Berges|first27=P.|last28=Bertucci|first28=B.|last29=Bigongiari|first29=G.|last30=Biland|first30=A.|display-authors=6|year=2013|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&nbsp;GeV|journal=Physical Review Letters|volume=110|issue=14|pages=141102 |pmid=25166975 |bibcode=2013PhRvL.110n1102A|doi=10.1103/PhysRevLett.110.141102|url=https://boa.unimib.it/bitstream/10281/44680/1/2013_PhysRevLett.110.141102_positron_fraction.pdf |archive-url=https://web.archive.org/web/20170813134328/https://boa.unimib.it/bitstream/10281/44680/1/2013_PhysRevLett.110.141102_positron_fraction.pdf |archive-date=2017-08-13 |url-status=live|doi-access=free}}</ref>

Cosmic ray antiprotons also have a much higher average 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|title=Secondary antiprotons and propagation of cosmic rays in the Galaxy and heliosphere|author1=Moskalenko, I.V.|author2=Strong, A.W.|author3=Ormes, J.F.|author4=Potgieter, M.S.|date=January 2002|journal=The Astrophysical Journal|volume=565|issue=1|pages=280–296|doi=10.1086/324402|arxiv=astro-ph/0106567|bibcode=2002ApJ...565..280M|s2cid=5863020}}</ref>

There is no evidence of complex antimatter atomic nuclei, such as [[antihelium]] nuclei (i.e., anti-alpha particles), in cosmic rays. These are actively being searched for. 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 at all, the ''AMS-01'' established an upper limit of {{nowrap|1.1 × 10<sup>−6</sup>}} for the antihelium to helium [[flux]] ratio.<ref>{{cite journal|collaboration=AMS Collaboration|last1=Aguilar|first1=M.|last2=Alcaraz|first2=J.|last3=Allaby|first3=J.|last4=Alpat|first4=B.|last5=Ambrosi|first5=G.|last6=Anderhub|first6=H.|last7=Ao|first7=L.|last8=Arefiev|first8=A.|display-authors=6|date=August 2002|title=The Alpha Magnetic Spectrometer (AMS) on the International Space Station: Part&nbsp;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>
{{multiple image||align=left|direction=vertical|header=The moon in cosmic rays|height=200|image1=Moon's shadow in muons.gif|alt1=The moon's muon shadow|caption1=The [[Moon]]'s cosmic ray shadow, as seen in secondary muons detected 700&nbsp;m below ground, at the [[Soudan 2|Soudan&nbsp;2]] detector|image2=Moon egret.jpg|alt2=The moon as seen in gamma rays|caption2=The Moon as seen by the [[Compton Gamma Ray Observatory]], in gamma rays with energies greater than 20&nbsp;MeV. These are produced by cosmic ray bombardment on its surface.<ref>{{cite web|date=1 August 2005|title=EGRET detection of gamma rays from the Moon|url=http://heasarc.gsfc.nasa.gov/docs/cgro/epo/news/gammoon.html |publisher=NASA|department=[[GSFC]]|access-date=11 February 2010}}</ref>}}