Editing Antiproton (section)

==Occurrence in nature==
Antiprotons have been detected in [[cosmic ray]]s beginning in 1979, first by balloon-borne experiments and more recently by satellite-based detectors. The standard picture for their presence in cosmic rays is that they are produced in collisions of cosmic ray protons with [[Atomic nucleus|atomic nuclei]] in the [[interstellar medium]], via the reaction, where A represents a nucleus:

{{SubatomicParticle|Proton}} + A → {{SubatomicParticle|Proton}} + {{SubatomicParticle|Antiproton}} + {{SubatomicParticle|Proton}} + A

The secondary antiprotons ({{SubatomicParticle|Antiproton}}) then propagate through the [[galaxy]], confined by the galactic [[magnetic field]]s. Their energy spectrum is modified by collisions with other atoms in the interstellar medium, and antiprotons can also be lost by "leaking out" of the galaxy.<ref name="Kennedy2000" />

The antiproton cosmic ray [[energy spectrum]] is now measured reliably and is consistent with this standard picture of antiproton production by cosmic ray collisions.<ref name="Kennedy2000">{{cite book |last=Kennedy |first=Dallas C. |chapter=High-energy Antimatter Telescope (HEAT): Basic design and performance |editor-first1=Brian D. |editor-first2=Thomas A. |editor-last1=Ramsey |editor-last2=Parnell |date=2000 |title=Gamma-Ray and Cosmic-Ray Detectors, Techniques, and Missions |series=[[Proceedings of SPIE]] |volume= 2806 |pages= 113–120 |arxiv=astro-ph/0003485 |doi=10.1117/12.253971 |s2cid=16664737 }}</ref> These experimental measurements set upper limits on the number of antiprotons that could be produced in exotic ways, such as from annihilation of [[Supersymmetry|supersymmetric]] [[dark matter]] particles in the galaxy or from the [[Hawking radiation]] caused by the evaporation of [[primordial black hole]]s. This also provides a lower limit on the antiproton lifetime of about 1–10 million years. Since the galactic storage time of antiprotons is about 10 million years, an intrinsic decay lifetime would modify the galactic residence time and distort the spectrum of cosmic ray antiprotons. This is significantly more stringent than the best laboratory measurements of the antiproton lifetime:

* [[LEAR]] collaboration at [[CERN]]: {{val|0.08|u=years}}
* [[Antihydrogen]] [[Penning trap]] of [[Gerald Gabrielse|Gabrielse]] et al.: {{val|0.28|u=years}}<ref>{{cite journal |last=Caso |first=C. |date=1998 |title=Particle Data Group |journal=European Physical Journal C |volume=3 |issue=1–4 |pages=1–783 |url=http://pdg.ihep.su/1999/s041.pdf |doi=10.1007/s10052-998-0104-x |bibcode=1998EPJC....3....1P |citeseerx=10.1.1.1017.4419 |s2cid=195314526 |display-authors=etal |access-date=2008-03-16 |archive-date=2011-07-16 |archive-url=https://web.archive.org/web/20110716074638/http://pdg.ihep.su/1999/s041.pdf |url-status=dead }}</ref>
* BASE experiment at CERN: {{val|10.2|u=years}}<ref>{{cite journal |last=Sellner |first=S. |date=2017 |title=Improved limit on the directly measured antiproton lifetime |journal=New Journal of Physics  |volume=19 |issue=8 |pages=083023 |url=http://stacks.iop.org/1367-2630/19/i=8/a=083023 |doi=10.1088/1367-2630/aa7e73 |bibcode=2017NJPh...19h3023S |display-authors=etal|doi-access=free }}</ref>
* APEX collaboration at [[Fermilab]]: {{val|50000|u=years}} for {{SubatomicParticle|Antiproton}} → {{SubatomicParticle|link=yes|Muon}} + anything
* APEX collaboration at Fermilab: {{val|300000|u=years}} for {{SubatomicParticle|Antiproton}} → {{SubatomicParticle|link=yes|Electron}} + {{SubatomicParticle|link=yes|Gamma}}

The magnitude of properties of the antiproton are predicted by [[CPT symmetry]] to be exactly related to those of the proton. In particular, CPT symmetry predicts the mass and lifetime of the antiproton to be the same as those of the proton, and the electric charge and magnetic moment of the antiproton to be opposite in sign and equal in magnitude to those of the proton. CPT symmetry is a basic consequence of [[quantum field theory]] and no violations of it have ever been detected.

===List of recent cosmic ray detection experiments===

* [[BESS (experiment)|BESS]]: balloon-borne experiment, flown in 1993, 1995, 1997, 2000, 2002, 2004 (Polar-I) and 2007 (Polar-II).
* CAPRICE: balloon-borne experiment, flown in 1994<ref>{{cite web |title=Cosmic AntiParticle Ring Imaging Cherenkov Experiment (CAPRICE) |url=http://ida1.physik.uni-siegen.de/caprice.html |publisher=Universität Siegen |access-date=14 April 2022 |archive-date=3 March 2016 |archive-url=https://web.archive.org/web/20160303203131/http://ida1.physik.uni-siegen.de/caprice.html |url-status=dead }}</ref> and 1998.
* HEAT: balloon-borne experiment, flown in 2000.
* [[Alpha Magnetic Spectrometer|AMS]]: space-based experiment, prototype flown on the [[Space Shuttle]] in 1998, intended for the [[International Space Station]], launched May 2011.
* [[Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics|PAMELA]]: satellite experiment to detect cosmic rays and antimatter from space, launched June 2006. Recent report discovered 28 antiprotons in the [[South Atlantic Anomaly]].<ref>{{cite journal | doi = 10.1088/2041-8205/737/2/L29 | title = The Discovery of Geomagnetically Trapped Cosmic-Ray Antiprotons | date = 2011 | last1 = Adriani | first1 = O. | last2 = Barbarino | first2 = G. C. | last3 = Bazilevskaya | first3 = G. A. | last4 = Bellotti | first4 = R. | last5 = Boezio | first5 = M. | last6 = Bogomolov | first6 = E. A. | last7 = Bongi | first7 = M. | last8 = Bonvicini | first8 = V. | last9 = Borisov | first9 = S. | journal = The Astrophysical Journal Letters | volume = 737 | issue = 2 | pages = L29 | bibcode = 2011ApJ...737L..29A | arxiv=1107.4882 | last10 = Bottai | first10 = S. | last11 = Bruno | first11 = A. | last12 = Cafagna | first12 = F. | last13 = Campana | first13 = D. | last14 = Carbone | first14 = R. | last15 = Carlson | first15 = P. | last16 = Casolino | first16 = M. | last17 = Castellini | first17 = G. | last18 = Consiglio | first18 = L. | last19 = De Pascale | first19 = M. P. | last20 = De Santis | first20 = C. | last21 = De Simone | first21 = N. | last22 = Di Felice | first22 = V. | last23 = Galper | first23 = A. M. | last24 = Gillard | first24 = W. | last25 = Grishantseva | first25 = L. | last26 = Jerse | first26 = G. | last27 = Karelin | first27 = A. V. | last28 = Kheymits | first28 = M. D. | last29 = Koldashov | first29 = S. V. | last30 = Krutkov | first30 = S. Y. | display-authors = 29 }}</ref>