Editing Antiproton (section)

==Modern experiments and applications==
[[File:Photocopy of photograph (original print located in LBNL Photo Lab Collection). Photographer unknown. October 6, 1955. BEV-938. ANTI-PROTON SET-UP WITH WORK GROUP; E. SEGRE, C. HAER CAL,1-BERK,4-34.tif|thumb|BEV-938. Antiproton set-up with work group: [[Emilio Segre]], [[Clyde Wiegand]], [[Edward J. Lofgren]], [[Owen Chamberlain]], [[Thomas Ypsilantis]], 1955]]

=== Production ===
Antiprotons were routinely produced at Fermilab for collider physics operations in the [[Tevatron]], where they were collided with protons. The use of antiprotons allows for a higher average energy of collisions between quarks and antiquarks than would be possible in proton–proton collisions. This is because the valence quarks 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]].

Formation of antiprotons requires energy equivalent to a temperature of 10 trillion [[Kelvin|K]] (10<sup>13</sup>&nbsp;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]].

=== Measurements ===
In July 2011, the [[ASACUSA]] experiment at CERN determined the mass of the antiproton to be {{val|1836.1526736|(23)}} times that of the electron.<ref name=Mhori>{{cite journal | journal=Nature | volume=475 |issue=7357 | pages=484–8 | date=2011 |last1=Hori |first1=M. |last2=Sótér | 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 | display-authors=8| pmid=21796208| arxiv=1304.4330 | s2cid=4376768 }}</ref> This is the same as the mass of a proton, within the level of certainty of the experiment.

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=Allan |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 |date=19 October 2017 |work=TechTimes.com |access-date=26 October 2017 }}</ref><ref name="NAT-20171020">{{cite journal |author=Smorra C.|display-authors=et al |title=A parts-per-billion measurement of the antiproton magnetic moment |date=20 October 2017 |journal=[[Nature (journal)|Nature]] |volume=550 |issue=7676 |pages=371–374 |doi=10.1038/nature24048 |pmid=29052625 |bibcode=2017Natur.550..371S |s2cid=205260736 |url=https://cds.cern.ch/record/2291601/files/nature24048.pdf |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.

In January 2022, by comparing the charge-to-mass ratios between antiproton and negatively charged hydrogen ion, the BASE experiment has determined the antiproton's charge-to-mass ratio is identical to the proton's, down to 16 parts per trillion.<ref>{{Cite web|title=BASE breaks new ground in matter–antimatter comparisons|url=http://home.cern/news/news/physics/base-breaks-new-ground-matter-antimatter-comparisons|access-date=2022-01-05|website=CERN|language=en}}</ref><ref>{{Cite journal|last1=Borchert|first1=M. J.|last2=Devlin|first2=J. A.|last3=Erlewein|first3=S. R.|last4=Fleck|first4=M.|last5=Harrington|first5=J. A.|last6=Higuchi|first6=T.|last7=Latacz|first7=B. M.|last8=Voelksen|first8=F.|last9=Wursten|first9=E. J.|last10=Abbass|first10=F.|last11=Bohman|first11=M. A.|date=2022-01-05|title=A 16-parts-per-trillion measurement of the antiproton-to-proton charge–mass ratio|url=https://www.nature.com/articles/s41586-021-04203-w|journal=Nature|volume=601 |issue=7891 |language=en|pages=53–57|doi=10.1038/s41586-021-04203-w|pmid=34987217 |bibcode=2022Natur.601...53B |s2cid=245709321 |issn=1476-4687}}</ref>

=== Possible applications ===
Antiprotons have been shown within laboratory experiments to have the potential to treat certain cancers, in a similar method currently used for [[Particle therapy|ion (proton) therapy]].<ref>{{cite journal|url=http://www.engr.psu.edu/antimatter/Papers/pbar_med.pdf |title=Antiproton portable traps and medical applications |date=1997 |url-status=dead |archive-url=https://web.archive.org/web/20110822150631/http://www.engr.psu.edu/antimatter/Papers/pbar_med.pdf |archive-date=2011-08-22 |doi=10.1023/A:1012653416870 |last1=Lewis |first1=R.A. |last2=Smith |first2=G.A. |last3=Howe |first3=S.D. |journal=Hyperfine Interactions |volume=109 |pages=155–164 }}</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.