BASE experiment - Revision history

Vigen at 10:56, 7 April 2026

2026-04-07T10:56:52Z

← Older revision		Revision as of 10:56, 7 April 2026
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	== BASE collaboration ==		== BASE collaboration ==
	The BASE collaboration comprises the following institutions:		The BASE collaboration comprises the following institutions:
	~~{{columns-list\|colwidth=30em\|~~
	*RIKEN, Japan		*RIKEN, Japan
	*University of Tokyo, Japan		*University of Tokyo, Japan
	*Max Planck Institute for Nuclear Physics]], Germany		*Max Planck Institute for Nuclear Physics, Germany
	*University of Mainz, Germany		*University of Mainz, Germany
	*GSI Helmholtz Centre for Heavy Ion Research~~\|GSI~~, Germany		*GSI Helmholtz Centre for Heavy Ion Research, Germany
	*Leibniz University Hannover, Germany		*Leibniz University Hannover, Germany
	*PTB, Braunschweig, Germany		*PTB, Braunschweig, Germany
	*ETH Zürich, Switzerland}}		*ETH Zürich, Switzerland

	For more information, see [[wikipedia:BASE experiment\|Wikipedia]].		For more information, see [[wikipedia:BASE experiment\|Wikipedia]].

Vigen at 10:54, 7 April 2026

2026-04-07T10:54:15Z

← Older revision		Revision as of 10:54, 7 April 2026
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	~~{{short description\|Multinational collaboration}}~~		'''BASE''' ('''B'''aryon '''A'''ntibaryon '''S'''ymmetry '''E'''xperiment), AD-8, is a multinational collaboration at the [[Antiproton Decelerator]] facility at [[CERN]], Geneva. The goal of the Japanese and German BASE collaboration<ref>{{cite news \|url=http://base.web.cern.ch\| title= official BASE website}}</ref> are high-precision investigations of the fundamental properties of the antiproton, namely the charge-to-mass ratio and the magnetic moment.
	~~{{Antiproton_Decelerator}}~~
	~~[[File:BASE logo.jpg\|thumb\|official BASE logo]]~~

	'''BASE''' ('''B'''aryon '''A'''ntibaryon '''S'''ymmetry '''E'''xperiment), AD-8, is a multinational collaboration at the [[Antiproton Decelerator]] facility at [[CERN]], Geneva. The goal of the Japanese and German BASE collaboration<ref>{{cite news \|url=http://base.web.cern.ch\| title= official BASE website}}</ref> are high-precision investigations of the fundamental properties of the [[antiproton]], namely the ~~[[Mass-to-charge ratio\|~~charge-to-mass ratio]] and the [[magnetic moment]].

	== Experimental setup ==		== Experimental setup ==
	The single antiprotons are stored in an advanced [[Penning trap]] system, which has a multi-trap system at its core. It consists of a reservoir trap,<ref>{{Cite journal \|last1=Smorra \|first1=C. \|last2=Mooser \|first2=A. \|last3=Franke \|first3=K. \|last4=Nagahama \|first4=H. \|last5=Schneider \|first5=G. \|last6=Higuchi \|first6=T. \|last7=Gorp \|first7=S. V. \|last8=Blaum \|first8=K. \|last9=Matsuda \|first9=Y. \|last10=Quint \|first10=W. \|last11=Walz \|first11=J. \|last12=Yamazaki \|first12=Y. \|last13=Ulmer \|first13=S. \|date=2015-10-15 \|title=A reservoir trap for antiprotons \|url=https://www.sciencedirect.com/science/article/pii/S1387380615002560 \|journal=International Journal of Mass Spectrometry \|language=en \|volume=389 \|pages=10–13 \|doi=10.1016/j.ijms.2015.08.007 \|arxiv=1507.04147 \|bibcode=2015IJMSp.389...10S \|s2cid=106405164 \|issn=1387-3806}}</ref> a precision trap, an analysis trap and a cooling trap. The reservoir trap has the capability to store antiprotons for several years<ref>{{Cite journal \|last1=Sellner \|first1=S \|last2=Besirli \|first2=M \|last3=Bohman \|first3=M \|last4=Borchert \|first4=M J \|last5=Harrington \|first5=J \|last6=Higuchi \|first6=T \|last7=Mooser \|first7=A \|last8=Nagahama \|first8=H \|last9=Schneider \|first9=G \|last10=Smorra \|first10=C \|last11=Tanaka \|first11=T \|last12=Blaum \|first12=K \|last13=Matsuda \|first13=Y \|last14=Ospelkaus \|first14=C \|last15=Quint \|first15=W \|date=2017-08-31 \|title=Improved limit on the directly measured antiproton lifetime \|journal=New Journal of Physics \|language=en \|volume=19 \|issue=8 \|page=083023 \|doi=10.1088/1367-2630/aa7e73 \|s2cid=125095370 \|issn=1367-2630\|doi-access=free \|bibcode=2017NJPh...19h3023S }}</ref> and allows BASE to operate experiments independent from accelerator cycles. The precision trap is for high precision frequency measurements, and the analysis trap has a strong magnetic field inhomogeneity superimposed, which is used for single particle ~~[[Spin-flip\|~~spin flip~~]] [[~~spectroscopy]]. By measuring the ~~[[Spin-flip\|~~spin flip]] rate as a function of the frequency of an externally applied magnetic-drive, a resonance curve is obtained. Together with a measurement of the ~~[[Cyclotron motion#Cyclotron resonance\|~~cyclotron frequency]], the magnetic moment is extracted.		The single antiprotons are stored in an advanced Penning trap system, which has a multi-trap system at its core. It consists of a reservoir trap,<ref>{{Cite journal \|last1=Smorra \|first1=C. \|last2=Mooser \|first2=A. \|last3=Franke \|first3=K. \|last4=Nagahama \|first4=H. \|last5=Schneider \|first5=G. \|last6=Higuchi \|first6=T. \|last7=Gorp \|first7=S. V. \|last8=Blaum \|first8=K. \|last9=Matsuda \|first9=Y. \|last10=Quint \|first10=W. \|last11=Walz \|first11=J. \|last12=Yamazaki \|first12=Y. \|last13=Ulmer \|first13=S. \|date=2015-10-15 \|title=A reservoir trap for antiprotons \|url=https://www.sciencedirect.com/science/article/pii/S1387380615002560 \|journal=International Journal of Mass Spectrometry \|language=en \|volume=389 \|pages=10–13 \|doi=10.1016/j.ijms.2015.08.007 \|arxiv=1507.04147 \|bibcode=2015IJMSp.389...10S \|s2cid=106405164 \|issn=1387-3806}}</ref> a precision trap, an analysis trap and a cooling trap. The reservoir trap has the capability to store antiprotons for several years<ref>{{Cite journal \|last1=Sellner \|first1=S \|last2=Besirli \|first2=M \|last3=Bohman \|first3=M \|last4=Borchert \|first4=M J \|last5=Harrington \|first5=J \|last6=Higuchi \|first6=T \|last7=Mooser \|first7=A \|last8=Nagahama \|first8=H \|last9=Schneider \|first9=G \|last10=Smorra \|first10=C \|last11=Tanaka \|first11=T \|last12=Blaum \|first12=K \|last13=Matsuda \|first13=Y \|last14=Ospelkaus \|first14=C \|last15=Quint \|first15=W \|date=2017-08-31 \|title=Improved limit on the directly measured antiproton lifetime \|journal=New Journal of Physics \|language=en \|volume=19 \|issue=8 \|page=083023 \|doi=10.1088/1367-2630/aa7e73 \|s2cid=125095370 \|issn=1367-2630\|doi-access=free \|bibcode=2017NJPh...19h3023S }}</ref> and allows BASE to operate experiments independent from accelerator cycles. The precision trap is for high precision frequency measurements, and the analysis trap has a strong magnetic field inhomogeneity superimposed, which is used for single particle spin flip spectroscopy. By measuring the spin flip rate as a function of the frequency of an externally applied magnetic-drive, a resonance curve is obtained. Together with a measurement of the cyclotron frequency, the magnetic moment is extracted.

	== BASE physics ==		== BASE physics ==
	The BASE collaboration developed techniques to observe the first ~~[[Spin-flip\|~~spin flips]] of a single trapped proton<ref>{{cite journal \|last1=Ulmer \|first1=S. \|display-authors=etal. \|title=Observation of Spin Flips with a Single Trapped Proton \|journal=[[Physical Review Letters]] \|date=20 June 2011 \|volume=106 \|issue=25 \|article-number=253001 \|doi=10.1103/PhysRevLett.106.253001\|pmid=21770638 \|bibcode=2011PhRvL.106y3001U \|arxiv = 1104.1206 \|s2cid=13997553 }}</ref> and applied the double-trap technique to measure the magnetic moment of the proton with a fractional precision of three parts in a billion,<ref>{{cite journal \|last1=Mooser \|first1=A. \|display-authors=etal \|year=2014 \|title=Direct high-precision measurement of the magnetic moment of the proton \|journal=[[Nature (journal)\|Nature]] \|volume=509 \|issue=7502 \|pages=596–599 \|doi=10.1038/nature13388\|pmid=24870545 \|bibcode=2014Natur.509..596M \|arxiv = 1406.4888 \|s2cid=4463940 }}</ref> later improved to a precision of 300 parts in a trillion,<ref>{{Cite journal \|last1=Schneider \|first1=Georg \|last2=Mooser \|first2=Andreas \|last3=Bohman \|first3=Matthew \|last4=Schön \|first4=Natalie \|last5=Harrington \|first5=James \|last6=Higuchi \|first6=Takashi \|last7=Nagahama \|first7=Hiroki \|last8=Sellner \|first8=Stefan \|last9=Smorra \|first9=Christian \|last10=Blaum \|first10=Klaus \|last11=Matsuda \|first11=Yasuyuki \|last12=Quint \|first12=Wolfgang \|last13=Walz \|first13=Jochen \|last14=Ulmer \|first14=Stefan \|date=2017-11-24 \|title=Double-trap measurement of the proton magnetic moment at 0.3 parts per billion precision \|journal=Science \|language=en \|volume=358 \|issue=6366 \|pages=1081–1084 \|doi=10.1126/science.aan0207 \|pmid=29170238 \|s2cid=206658547 \|issn=0036-8075\|doi-access=free \|bibcode=2017Sci...358.1081S }}</ref> being the most precise measurement of this fundamental property of the proton. With the invention of a two particle/three trap technique BASE measured the antiproton magnetic moment with a fractional accuracy of 1.5 parts in a billion, which improved the previous most precise proton/antiproton comparison in that sector <ref>{{Cite journal \|last1=ATRAP Collaboration \|last2=DiSciacca \|first2=J. \|last3=Marshall \|first3=M. \|last4=Marable \|first4=K. \|last5=Gabrielse \|first5=G. \|last6=Ettenauer \|first6=S. \|last7=Tardiff \|first7=E. \|last8=Kalra \|first8=R. \|last9=Fitzakerley \|first9=D. W. \|last10=George \|first10=M. C. \|last11=Hessels \|first11=E. A. \|last12=Storry \|first12=C. H. \|last13=Weel \|first13=M. \|last14=Grzonka \|first14=D. \|last15=Oelert \|first15=W. \|date=2013-03-25 \|title=One-Particle Measurement of the Antiproton Magnetic Moment \|journal=Physical Review Letters \|volume=110 \|issue=13 \|article-number=130801 \|doi=10.1103/PhysRevLett.110.130801\|pmid=23581304 \|s2cid=14943420 \|doi-access=free \|arxiv=1301.6310 \|bibcode=2013PhRvL.110m0801D }}</ref> by more than a factor of 3000. This measurement constitutes one of the most stringent tests of ~~[[CPT symmetry\|~~CPT invariance]] with baryons to date, and sets the most stringent limits on antimatter/dark matter interaction to date.<ref>{{Cite journal \|last1=ATRAP Collaboration \|last2=DiSciacca \|first2=J. \|last3=Marshall \|first3=M. \|last4=Marable \|first4=K. \|last5=Gabrielse \|first5=G. \|last6=Ettenauer \|first6=S. \|last7=Tardiff \|first7=E. \|last8=Kalra \|first8=R. \|last9=Fitzakerley \|first9=D. W. \|last10=George \|first10=M. C. \|last11=Hessels \|first11=E. A. \|last12=Storry \|first12=C. H. \|last13=Weel \|first13=M. \|last14=Grzonka \|first14=D. \|last15=Oelert \|first15=W. \|date=2013-03-25 \|title=One-Particle Measurement of the Antiproton Magnetic Moment \|journal=Physical Review Letters \|volume=110 \|issue=13 \|article-number=130801 \|doi=10.1103/PhysRevLett.110.130801\|pmid=23581304 \|s2cid=14943420 \|doi-access=free \|arxiv=1301.6310 \|bibcode=2013PhRvL.110m0801D }}</ref>		The BASE collaboration developed techniques to observe the first spin flips of a single trapped proton<ref>{{cite journal \|last1=Ulmer \|first1=S. \|display-authors=etal. \|title=Observation of Spin Flips with a Single Trapped Proton \|journal=[[Physical Review Letters]] \|date=20 June 2011 \|volume=106 \|issue=25 \|article-number=253001 \|doi=10.1103/PhysRevLett.106.253001\|pmid=21770638 \|bibcode=2011PhRvL.106y3001U \|arxiv = 1104.1206 \|s2cid=13997553 }}</ref> and applied the double-trap technique to measure the magnetic moment of the proton with a fractional precision of three parts in a billion,<ref>{{cite journal \|last1=Mooser \|first1=A. \|display-authors=etal \|year=2014 \|title=Direct high-precision measurement of the magnetic moment of the proton \|journal=[[Nature (journal)\|Nature]] \|volume=509 \|issue=7502 \|pages=596–599 \|doi=10.1038/nature13388\|pmid=24870545 \|bibcode=2014Natur.509..596M \|arxiv = 1406.4888 \|s2cid=4463940 }}</ref> later improved to a precision of 300 parts in a trillion,<ref>{{Cite journal \|last1=Schneider \|first1=Georg \|last2=Mooser \|first2=Andreas \|last3=Bohman \|first3=Matthew \|last4=Schön \|first4=Natalie \|last5=Harrington \|first5=James \|last6=Higuchi \|first6=Takashi \|last7=Nagahama \|first7=Hiroki \|last8=Sellner \|first8=Stefan \|last9=Smorra \|first9=Christian \|last10=Blaum \|first10=Klaus \|last11=Matsuda \|first11=Yasuyuki \|last12=Quint \|first12=Wolfgang \|last13=Walz \|first13=Jochen \|last14=Ulmer \|first14=Stefan \|date=2017-11-24 \|title=Double-trap measurement of the proton magnetic moment at 0.3 parts per billion precision \|journal=Science \|language=en \|volume=358 \|issue=6366 \|pages=1081–1084 \|doi=10.1126/science.aan0207 \|pmid=29170238 \|s2cid=206658547 \|issn=0036-8075\|doi-access=free \|bibcode=2017Sci...358.1081S }}</ref> being the most precise measurement of this fundamental property of the proton. With the invention of a two particle/three trap technique BASE measured the antiproton magnetic moment with a fractional accuracy of 1.5 parts in a billion, which improved the previous most precise proton/antiproton comparison in that sector <ref>{{Cite journal \|last1=ATRAP Collaboration \|last2=DiSciacca \|first2=J. \|last3=Marshall \|first3=M. \|last4=Marable \|first4=K. \|last5=Gabrielse \|first5=G. \|last6=Ettenauer \|first6=S. \|last7=Tardiff \|first7=E. \|last8=Kalra \|first8=R. \|last9=Fitzakerley \|first9=D. W. \|last10=George \|first10=M. C. \|last11=Hessels \|first11=E. A. \|last12=Storry \|first12=C. H. \|last13=Weel \|first13=M. \|last14=Grzonka \|first14=D. \|last15=Oelert \|first15=W. \|date=2013-03-25 \|title=One-Particle Measurement of the Antiproton Magnetic Moment \|journal=Physical Review Letters \|volume=110 \|issue=13 \|article-number=130801 \|doi=10.1103/PhysRevLett.110.130801\|pmid=23581304 \|s2cid=14943420 \|doi-access=free \|arxiv=1301.6310 \|bibcode=2013PhRvL.110m0801D }}</ref> by more than a factor of 3000. This measurement constitutes one of the most stringent tests of CPT invariance with baryons to date, and sets the most stringent limits on antimatter/dark matter interaction to date.<ref>{{Cite journal \|last1=ATRAP Collaboration \|last2=DiSciacca \|first2=J. \|last3=Marshall \|first3=M. \|last4=Marable \|first4=K. \|last5=Gabrielse \|first5=G. \|last6=Ettenauer \|first6=S. \|last7=Tardiff \|first7=E. \|last8=Kalra \|first8=R. \|last9=Fitzakerley \|first9=D. W. \|last10=George \|first10=M. C. \|last11=Hessels \|first11=E. A. \|last12=Storry \|first12=C. H. \|last13=Weel \|first13=M. \|last14=Grzonka \|first14=D. \|last15=Oelert \|first15=W. \|date=2013-03-25 \|title=One-Particle Measurement of the Antiproton Magnetic Moment \|journal=Physical Review Letters \|volume=110 \|issue=13 \|article-number=130801 \|doi=10.1103/PhysRevLett.110.130801\|pmid=23581304 \|s2cid=14943420 \|doi-access=free \|arxiv=1301.6310 \|bibcode=2013PhRvL.110m0801D }}</ref>

	Inspired by this work BASE has also used Penning trap detectors as axion haloscopes, and derived stringent narrow-band laboratory limits on the conversion of axions to photons.<ref>{{Cite journal \|last1=Devlin \|first1=Jack A. \|last2=Borchert \|first2=Matthias J. \|last3=Erlewein \|first3=Stefan \|last4=Fleck \|first4=Markus \|last5=Harrington \|first5=James A. \|last6=Latacz \|first6=Barbara \|last7=Warncke \|first7=Jan \|last8=Wursten \|first8=Elise \|last9=Bohman \|first9=Matthew A. \|last10=Mooser \|first10=Andreas H. \|last11=Smorra \|first11=Christian \|last12=Wiesinger \|first12=Markus \|last13=Will \|first13=Christian \|last14=Blaum \|first14=Klaus \|last15=Matsuda \|first15=Yasuyuki \|date=2021-01-25 \|title=Constraints on the Coupling between Axionlike Dark Matter and Photons Using an Antiproton Superconducting Tuned Detection Circuit in a Cryogenic Penning Trap \|journal=Physical Review Letters \|volume=126 \|issue=4 \|article-number=041301 \|doi=10.1103/PhysRevLett.126.041301\|pmid=33576660 \|s2cid=231719186 \|doi-access=free \|arxiv=2101.11290 \|bibcode=2021PhRvL.126d1301D }}</ref>		Inspired by this work BASE has also used Penning trap detectors as axion haloscopes, and derived stringent narrow-band laboratory limits on the conversion of axions to photons.<ref>{{Cite journal \|last1=Devlin \|first1=Jack A. \|last2=Borchert \|first2=Matthias J. \|last3=Erlewein \|first3=Stefan \|last4=Fleck \|first4=Markus \|last5=Harrington \|first5=James A. \|last6=Latacz \|first6=Barbara \|last7=Warncke \|first7=Jan \|last8=Wursten \|first8=Elise \|last9=Bohman \|first9=Matthew A. \|last10=Mooser \|first10=Andreas H. \|last11=Smorra \|first11=Christian \|last12=Wiesinger \|first12=Markus \|last13=Will \|first13=Christian \|last14=Blaum \|first14=Klaus \|last15=Matsuda \|first15=Yasuyuki \|date=2021-01-25 \|title=Constraints on the Coupling between Axionlike Dark Matter and Photons Using an Antiproton Superconducting Tuned Detection Circuit in a Cryogenic Penning Trap \|journal=Physical Review Letters \|volume=126 \|issue=4 \|article-number=041301 \|doi=10.1103/PhysRevLett.126.041301\|pmid=33576660 \|s2cid=231719186 \|doi-access=free \|arxiv=2101.11290 \|bibcode=2021PhRvL.126d1301D }}</ref>

	In 2022 BASE measured that the charge-to-mass ratios of protons and antiprotons are equal within a precision of 16 parts per trillion.<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=2022-01-06\|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\|language=en\|volume=601\|issue=7891\|pages=53–57\|doi=10.1038/s41586-021-04203-w\|pmid=34987217 \|bibcode=2022Natur.601...53B \|s2cid=256822230 \|issn=0028-0836\|url-access=subscription}}</ref><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=2022-01-14\|website=CERN\|language=en}}</ref> This measurement constitutes the most precise test of CPT invariance in the baryon sector and sets the first differential constraints on the clock weak [[equivalence principle]] using baryonic antimatter.		In 2022 BASE measured that the charge-to-mass ratios of protons and antiprotons are equal within a precision of 16 parts per trillion.<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=2022-01-06\|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\|language=en\|volume=601\|issue=7891\|pages=53–57\|doi=10.1038/s41586-021-04203-w\|pmid=34987217 \|bibcode=2022Natur.601...53B \|s2cid=256822230 \|issn=0028-0836\|url-access=subscription}}</ref><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=2022-01-14\|website=CERN\|language=en}}</ref> This measurement constitutes the most precise test of CPT invariance in the baryon sector and sets the first differential constraints on the clock weak equivalence principle using baryonic antimatter.

	== BASE collaboration ==		== BASE collaboration ==
	~~[[File:Base11.jpg\|thumb\|250x250px\|Views of the BASE experimental zone]]~~
	~~[[File:Base2.jpg\|thumb\|209x209px\|Views of the BASE experimental zone]]~~
	The BASE collaboration comprises the following institutions:		The BASE collaboration comprises the following institutions:
	{{columns-list\|colwidth=30em\|		{{columns-list\|colwidth=30em\|
	*[[RIKEN]], Japan		*RIKEN, Japan
	*[[University of Tokyo]], Japan		*University of Tokyo, Japan
	*[[Max Planck Institute for Nuclear Physics]], Germany		*Max Planck Institute for Nuclear Physics]], Germany
	*[[University of Mainz]], Germany		*University of Mainz, Germany
	*[[GSI Helmholtz Centre for Heavy Ion Research\|GSI]], Germany		*GSI Helmholtz Centre for Heavy Ion Research\|GSI, Germany
	*[[Leibniz University Hannover]], Germany		*Leibniz University Hannover, Germany
	*[[PTB, Braunschweig]], Germany		*PTB, Braunschweig, Germany
	*[[ETH Zürich]], Switzerland}}		*ETH Zürich, Switzerland}}


			For more information, see [[wikipedia:BASE experiment\|Wikipedia]].


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	== External links ==		== External links ==
	Record for [https://inspirehep.net/experiments/1275753 BASE Experiment] on [[INSPIRE-HEP]]		Record for [https://inspirehep.net/experiments/1275753 BASE Experiment] on INSPIRE-HEP
	[[Category:~~Particle~~ experiments]]		[[Category:AD experiments]]
	[[Category:~~CERN experiments~~]]		[[Category:Pages linking to Wikipedia]]

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{{short description|Multinational collaboration}}
{{Antiproton_Decelerator}}
[[File:BASE logo.jpg|thumb|official BASE logo]]

'''BASE''' ('''B'''aryon '''A'''ntibaryon '''S'''ymmetry '''E'''xperiment), AD-8, is a multinational collaboration at the [[Antiproton Decelerator]] facility at [[CERN]], Geneva. The goal of the Japanese and German BASE collaboration<ref>{{cite news |url=http://base.web.cern.ch| title= official BASE website}}</ref> are high-precision investigations of the fundamental properties of the [[antiproton]], namely the [[Mass-to-charge ratio|charge-to-mass ratio]] and the [[magnetic moment]].

== Experimental setup ==
The single antiprotons are stored in an advanced [[Penning trap]] system, which has a multi-trap system at its core. It consists of a reservoir trap,<ref>{{Cite journal |last1=Smorra |first1=C. |last2=Mooser |first2=A. |last3=Franke |first3=K. |last4=Nagahama |first4=H. |last5=Schneider |first5=G. |last6=Higuchi |first6=T. |last7=Gorp |first7=S. V. |last8=Blaum |first8=K. |last9=Matsuda |first9=Y. |last10=Quint |first10=W. |last11=Walz |first11=J. |last12=Yamazaki |first12=Y. |last13=Ulmer |first13=S. |date=2015-10-15 |title=A reservoir trap for antiprotons |url=https://www.sciencedirect.com/science/article/pii/S1387380615002560 |journal=International Journal of Mass Spectrometry |language=en |volume=389 |pages=10–13 |doi=10.1016/j.ijms.2015.08.007 |arxiv=1507.04147 |bibcode=2015IJMSp.389...10S |s2cid=106405164 |issn=1387-3806}}</ref> a precision trap, an analysis trap and a cooling trap. The reservoir trap has the capability to store antiprotons for several years<ref>{{Cite journal |last1=Sellner |first1=S |last2=Besirli |first2=M |last3=Bohman |first3=M |last4=Borchert |first4=M J |last5=Harrington |first5=J |last6=Higuchi |first6=T |last7=Mooser |first7=A |last8=Nagahama |first8=H |last9=Schneider |first9=G |last10=Smorra |first10=C |last11=Tanaka |first11=T |last12=Blaum |first12=K |last13=Matsuda |first13=Y |last14=Ospelkaus |first14=C |last15=Quint |first15=W |date=2017-08-31 |title=Improved limit on the directly measured antiproton lifetime |journal=New Journal of Physics |language=en |volume=19 |issue=8 |page=083023 |doi=10.1088/1367-2630/aa7e73 |s2cid=125095370 |issn=1367-2630|doi-access=free |bibcode=2017NJPh...19h3023S }}</ref> and allows BASE to operate experiments independent from accelerator cycles. The precision trap is for high precision frequency measurements, and the analysis trap has a strong magnetic field inhomogeneity superimposed, which is used for single particle [[Spin-flip|spin flip]] [[spectroscopy]]. By measuring the [[Spin-flip|spin flip]] rate as a function of the frequency of an externally applied magnetic-drive, a resonance curve is obtained. Together with a measurement of the [[Cyclotron motion#Cyclotron resonance|cyclotron frequency]], the magnetic moment is extracted.

== BASE physics ==
The BASE collaboration developed techniques to observe the first [[Spin-flip|spin flips]] of a single trapped proton<ref>{{cite journal |last1=Ulmer |first1=S. |display-authors=etal. |title=Observation of Spin Flips with a Single Trapped Proton |journal=[[Physical Review Letters]] |date=20 June 2011 |volume=106 |issue=25 |article-number=253001 |doi=10.1103/PhysRevLett.106.253001|pmid=21770638 |bibcode=2011PhRvL.106y3001U |arxiv = 1104.1206 |s2cid=13997553 }}</ref> and applied the double-trap technique to measure the magnetic moment of the proton with a fractional precision of three parts in a billion,<ref>{{cite journal |last1=Mooser |first1=A. |display-authors=etal |year=2014 |title=Direct high-precision measurement of the magnetic moment of the proton |journal=[[Nature (journal)|Nature]] |volume=509 |issue=7502 |pages=596–599 |doi=10.1038/nature13388|pmid=24870545 |bibcode=2014Natur.509..596M |arxiv = 1406.4888 |s2cid=4463940 }}</ref> later improved to a precision of 300 parts in a trillion,<ref>{{Cite journal |last1=Schneider |first1=Georg |last2=Mooser |first2=Andreas |last3=Bohman |first3=Matthew |last4=Schön |first4=Natalie |last5=Harrington |first5=James |last6=Higuchi |first6=Takashi |last7=Nagahama |first7=Hiroki |last8=Sellner |first8=Stefan |last9=Smorra |first9=Christian |last10=Blaum |first10=Klaus |last11=Matsuda |first11=Yasuyuki |last12=Quint |first12=Wolfgang |last13=Walz |first13=Jochen |last14=Ulmer |first14=Stefan |date=2017-11-24 |title=Double-trap measurement of the proton magnetic moment at 0.3 parts per billion precision |journal=Science |language=en |volume=358 |issue=6366 |pages=1081–1084 |doi=10.1126/science.aan0207 |pmid=29170238 |s2cid=206658547 |issn=0036-8075|doi-access=free |bibcode=2017Sci...358.1081S }}</ref> being the most precise measurement of this fundamental property of the proton. With the invention of a two particle/three trap technique BASE measured the antiproton magnetic moment with a fractional accuracy of 1.5 parts in a billion, which improved the previous most precise proton/antiproton comparison in that sector <ref>{{Cite journal |last1=ATRAP Collaboration |last2=DiSciacca |first2=J. |last3=Marshall |first3=M. |last4=Marable |first4=K. |last5=Gabrielse |first5=G. |last6=Ettenauer |first6=S. |last7=Tardiff |first7=E. |last8=Kalra |first8=R. |last9=Fitzakerley |first9=D. W. |last10=George |first10=M. C. |last11=Hessels |first11=E. A. |last12=Storry |first12=C. H. |last13=Weel |first13=M. |last14=Grzonka |first14=D. |last15=Oelert |first15=W. |date=2013-03-25 |title=One-Particle Measurement of the Antiproton Magnetic Moment |journal=Physical Review Letters |volume=110 |issue=13 |article-number=130801 |doi=10.1103/PhysRevLett.110.130801|pmid=23581304 |s2cid=14943420 |doi-access=free |arxiv=1301.6310 |bibcode=2013PhRvL.110m0801D }}</ref> by more than a factor of 3000. This measurement constitutes one of the most stringent tests of [[CPT symmetry|CPT invariance]] with baryons to date, and sets the most stringent limits on antimatter/dark matter interaction to date.<ref>{{Cite journal |last1=ATRAP Collaboration |last2=DiSciacca |first2=J. |last3=Marshall |first3=M. |last4=Marable |first4=K. |last5=Gabrielse |first5=G. |last6=Ettenauer |first6=S. |last7=Tardiff |first7=E. |last8=Kalra |first8=R. |last9=Fitzakerley |first9=D. W. |last10=George |first10=M. C. |last11=Hessels |first11=E. A. |last12=Storry |first12=C. H. |last13=Weel |first13=M. |last14=Grzonka |first14=D. |last15=Oelert |first15=W. |date=2013-03-25 |title=One-Particle Measurement of the Antiproton Magnetic Moment |journal=Physical Review Letters |volume=110 |issue=13 |article-number=130801 |doi=10.1103/PhysRevLett.110.130801|pmid=23581304 |s2cid=14943420 |doi-access=free |arxiv=1301.6310 |bibcode=2013PhRvL.110m0801D }}</ref>

Inspired by this work BASE has also used Penning trap detectors as axion haloscopes, and derived stringent narrow-band laboratory limits on the conversion of axions to photons.<ref>{{Cite journal |last1=Devlin |first1=Jack A. |last2=Borchert |first2=Matthias J. |last3=Erlewein |first3=Stefan |last4=Fleck |first4=Markus |last5=Harrington |first5=James A. |last6=Latacz |first6=Barbara |last7=Warncke |first7=Jan |last8=Wursten |first8=Elise |last9=Bohman |first9=Matthew A. |last10=Mooser |first10=Andreas H. |last11=Smorra |first11=Christian |last12=Wiesinger |first12=Markus |last13=Will |first13=Christian |last14=Blaum |first14=Klaus |last15=Matsuda |first15=Yasuyuki |date=2021-01-25 |title=Constraints on the Coupling between Axionlike Dark Matter and Photons Using an Antiproton Superconducting Tuned Detection Circuit in a Cryogenic Penning Trap |journal=Physical Review Letters |volume=126 |issue=4 |article-number=041301 |doi=10.1103/PhysRevLett.126.041301|pmid=33576660 |s2cid=231719186 |doi-access=free |arxiv=2101.11290 |bibcode=2021PhRvL.126d1301D }}</ref>

In 2022 BASE measured that the charge-to-mass ratios of protons and antiprotons are equal within a precision of 16 parts per trillion.<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=2022-01-06|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|language=en|volume=601|issue=7891|pages=53–57|doi=10.1038/s41586-021-04203-w|pmid=34987217 |bibcode=2022Natur.601...53B |s2cid=256822230 |issn=0028-0836|url-access=subscription}}</ref><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=2022-01-14|website=CERN|language=en}}</ref> This measurement constitutes the most precise test of CPT invariance in the baryon sector and sets the first differential constraints on the clock weak [[equivalence principle]] using baryonic antimatter.

== BASE collaboration ==
[[File:Base11.jpg|thumb|250x250px|Views of the BASE experimental zone]]
[[File:Base2.jpg|thumb|209x209px|Views of the BASE experimental zone]]
The BASE collaboration comprises the following institutions:
{{columns-list|colwidth=30em|
*[[RIKEN]], Japan
*[[University of Tokyo]], Japan
*[[Max Planck Institute for Nuclear Physics]], Germany
*[[University of Mainz]], Germany
*[[GSI Helmholtz Centre for Heavy Ion Research|GSI]], Germany
*[[Leibniz University Hannover]], Germany
*[[PTB, Braunschweig]], Germany
*[[ETH Zürich]], Switzerland}}

== See also ==

# [[Antiproton Decelerator]]
# [[TRAP experiment]]
# [[ATRAP experiment]]

== References ==
{{Reflist}}

== External links ==
Record for [https://inspirehep.net/experiments/1275753 BASE Experiment] on [[INSPIRE-HEP]]
[[Category:Particle experiments]]
[[Category:CERN experiments]]