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| {{Infobox particle
| | Hi, everybody! <br>I'm Spanish female ;=). <br>I really love Fishkeeping!<br><br>Also visit my web blog: [http://Myepix.de/index.php?site=profile&id=117359 How to Get free Fifa 15 coins] |
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| | name = Antiproton
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| | image = [[Image:Quark structure antiproton.svg|200px]]
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| | caption = The quark structure of the antiproton.
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| | num_types =
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| | classification = [[Antibaryon]]
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| | composition = 2 [[up quark|up antiquarks]], 1 [[down quark|down antiquark]]
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| | statistics = [[Fermionic]]
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| | group = Hadron
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| | generation =
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| | interaction = [[Strong interaction|Strong]], [[Weak interaction|Weak]], [[Electromagnetic force|Electromagnetic]], [[Gravity]]
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| | particle = [[Proton]]
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| | antiparticle =
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| | status = Discovered
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| | theorized =
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| | discovered = [[Emilio Segrè]] & [[Owen Chamberlain]] (1955)
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| | symbol = {{SubatomicParticle|Antiproton}}
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| | mass = 938 [[electronvolt|MeV]]/[[speed of light|c]]<sup>2</sup>
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| | mean_lifetime =
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| | decay_particle =
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| | electric_charge = −1 [[elementary charge|e]]
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| | charge_radius =
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| | electric_dipole_moment =
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| | electric_polarizability =
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| | magnetic_moment =
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| | magnetic_polarizability =
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| | color_charge =
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| | spin = {{frac|1|2}}
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| | num_spin_states =
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| | lepton_number =
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| | baryon_number =
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| | strangeness =
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| | charm =
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| | bottomness =
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| | topness =
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| | isospin = {{frac|1|2}}
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| | weak_isospin =
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| | hypercharge =
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| | weak_hypercharge =
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| | parity =
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| | g_parity =
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| | c_parity =
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| | r_parity =
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| | condensed_symmetries =
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| }}
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| {{antimatter}}
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| The '''antiproton''', {{SubatomicParticle|Antiproton}}, pronounced ''p-bar'') is the [[antiparticle]] of the [[proton]]. Antiprotons are stable, but they are typically short-lived since any collision with a proton will cause both particles to be [[annihilation|annihilated]] in a burst of energy.
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| The existence of the antiproton with −1 electric charge, opposite to the +1 electric charge of the proton, was predicted by [[Paul Dirac]] in his 1933 Nobel Prize lecture.<ref>
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| {{Cite web
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| | last = Dirac
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| | first = Paul A. M.
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| | title = Theory of electrons and positrons
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| | year = 1933
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| | url = http://nobelprize.org/nobel_prizes/physics/laureates/1933/dirac-lecture.pdf
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| | postscript = <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}}
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| }}
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| </ref> Dirac received the Nobel Prize for his previous 1928 publication of his [[Dirac Equation]] that predicted the existence of positive and negative solutions to the Energy Equation (<math>E = mc^2</math>) of Einstein and the existence of the [[positron]], the antimatter analog to the electron, with positive charge and opposite spin. | |
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| 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]]. An antiproton consists of two up [[antiquark]]s and one down antiquark ({{SubatomicParticle|link=yes|Up antiquark}}{{SubatomicParticle|link=yes|Up antiquark}}{{SubatomicParticle|link=yes|Down antiquark}}). The properties of the antiproton that have been measured all match the corresponding properties of the proton, with the exception that the antiproton has electric charge and magnetic moment that are the opposites of those in the proton. The questions of how matter is different from antimatter, and the relevance of antimatter in explaining how our universe survived the [[Big Bang]] remain open problems - open, in part, due to the relative dearth of [[antimatter]] in today's universe.{{Citation needed|date=February 2007}}
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| ==Occurrence in nature==
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| Antiprotons have been detected in [[cosmic ray]]s for over 25 years, 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 [[proton]]s with nuclei in the [[interstellar medium]], via the reaction, where A represents a nucleus:
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| {{SubatomicParticle|Proton}} + A → {{SubatomicParticle|Proton}}+ {{SubatomicParticle|Antiproton}} +{{SubatomicParticle|Proton}}+ A
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| 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"{{citation needed|date=August 2010}}<!--this makes little sense as is, please provide more details...--> of the galaxy.
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| 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>{{cite journal |last=Kennedy |first=Dallas C. |authorlink= |coauthors= |year=2000 |month= |title=Cosmic Ray Antiprotons |journal=[[Proc. SPIE]] |volume= 2806|issue= |pages= 113|id= |arxiv=astro-ph/0003485 |quote=|doi=10.1117/12.253971 |series=Gamma-Ray and Cosmic-Ray Detectors, Techniques, and Missions |editor1-last=Ramsey |editor1-first=Brian D |first2=S. W. |first3=A. |first4=James J. |first5=C. R. |first6=C. |first7=G. |first8=Don |first9=D. |first10=J. |first11=D. M. |first12=Steven M. |first13=Dietrich |first14=J. A. |first15=S. L. |first16=E. |first17=Simon P. |first18=K. K. |first19=Gregory |first20=Andrew D. |first21=E. |editor2-last=Parnell |editor2-first=Thomas A }}</ref> This sets 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|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:
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| * [[LEAR]] collaboration at [[CERN]]: {{val|0.08|u=years}}
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| * [[Antihydrogen]] [[Penning trap]] of Gabrielse et al.: {{val|0.28|u=years}}<ref>{{cite journal |last=Caso |first=C. |authorlink= |coauthors=''et al.'' |year=1998 |month= |title=Particle Data Group |journal=European Physical Journal C |volume=3 |issue= |pages=613 |id= |url=http://pdg.ihep.su/1999/s041.pdf |doi=10.1007/s10052-998-0104-x |bibcode = 1998EPJC....3....1P }}</ref>
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| * APEX collaboration at [[Fermilab]]: {{val|fmt=commas|50000|u=years}} for {{SubatomicParticle|Antiproton}} → {{SubatomicParticle|link=yes|Muon}} + anything
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| * APEX collaboration at Fermilab: {{val|fmt=commas|300000|u=years}} for {{SubatomicParticle|Antiproton}} → {{SubatomicParticle|link=yes|Electron}} + {{SubatomicParticle|link=yes|Gamma}}
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| 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.
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| ===List of recent antiproton cosmic ray detection experiments===
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| * [[BESS]]: balloon-borne experiment, flown in 1993, 1995, 1997, 2000, 2002, 2004 (Polar-I) and 2007 (Polar-II).
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| * CAPRICE: balloon-borne experiment, flown in 1994<ref>[http://ida1.physik.uni-siegen.de/caprice.html Caprice Experiment<!-- Bot generated title -->]</ref> and 1998.
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| * HEAT: balloon-borne experiment, flown in 2000.
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| * [[Alpha Magnetic Spectrometer|AMS]]: space-based experiment, prototype flown on the [[space shuttle]] in 1998, intended for the [[International Space Station]], launched May 2011.
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| * [[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 | year = 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=1107.4882v1 | 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. }}</ref>
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| ==Modern experiments and applications==
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| Antiprotons are routinely produced at [[Fermilab]] for collider physics operations in the [[Tevatron]], where they are collided with protons. The use of antiprotons allows for a higher average energy of collisions between [[quark]]s and [[antiquark]]s than would be possible in proton-proton collisions. This is because the [[valence quark]]s in the proton, and the valence antiquarks in the antiproton, tend to carry the largest [[Parton (particle physics)|fraction of the proton or antiproton's momentum]].
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| Their formation requires energy equivalent to a temperature of 10 trillion [[Kelvin|K]] (10<sup>13</sup> K) and this does not tend to happen naturally. However, at [[CERN]], protons are accelerated in the Proton [[Synchrotron]] to an energy of 26 [[giga|G]][[electron volt|eV]], and then smashed into an [[iridium]] rod. The protons bounce off the iridium nuclei with [[mass-energy equivalence|enough energy for matter to be created]]. A range of particles and antiparticles are formed, and the antiprotons are separated off using magnets in [[vacuum]].
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| In July 2011, the [[ASACUSA]] experiment at CERN determined the mass of the antiproton to be {{val|fmt=commas|1836.1536736|(23)}} times more massive than an [[electron]].<ref name=Mhori>{{cite journal | journal=Nature | volume=475 |issue=7357 | pages=484–8 | year=2011 |last=Hori |first=M. |last2=''et al.'' | title=Two-photon laser spectroscopy of antiprotonic helium and the antiproton-to-electron mass ratio |doi=10.1038/nature10260 | first2=Anna | last3=Barna | first3=Daniel | last4=Dax | first4=Andreas | last5=Hayano | first5=Ryugo | last6=Friedreich | first6=Susanne | last7=Juhász | first7=Bertalan | last8=Pask | first8=Thomas | last9=Widmann | first9=Eberhard | displayauthors=8| pmid=21796208 | first10=Dezső | first11=Luca | first12=Nicola}}</ref> This is the same as the mass of a proton, within the level of certainty of the experiment.
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| Antiprotons have 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 web|url=http://www.engr.psu.edu/antimatter/Papers/pbar_med.pdf|title=Antiproton portable traps and medical applications}}</ref> The primary difference between antiproton therapy and proton therapy is that following ion energy deposition the antiproton annihilates depositing additional energy in the cancerous region.
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| ==See also==
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| *[[Antimatter]]
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| *[[Antineutron]]
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| *[[Positron]]
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| *[[Antihydrogen]]
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| *[[Antiprotonic helium]]
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| *[[List of particles]]
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| == References ==
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| {{Reflist}}
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| {{Particles}}
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| [[Category:Antimatter]]
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| [[Category:Baryons]]
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| [[Category:Nucleons]]
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Hi, everybody!
I'm Spanish female ;=).
I really love Fishkeeping!
Also visit my web blog: How to Get free Fifa 15 coins