View source for B–Bbar oscillation

'''Neutral B meson oscillations''' (or '''{{SubatomicParticle|B}}–{{SubatomicParticle|AntiB}} oscillations''') are one of the manifestations of the [[neutral particle oscillation]], a fundamental prediction of the [[Standard Model]] of [[particle physics]]. It is the phenomenon of [[B meson]]s changing (or ''oscillating'') between their [[matter]] and [[antimatter]] forms before their decay. The [[strange B meson|{{SubatomicParticle|strange B}} meson]] can exist as either a bound state of a [[strange quark|strange antiquark]] and a [[bottom quark]], or a strange quark and bottom antiquark. The oscillations in the neutral B sector are analogous to the phenomena that produce long and short-lived neutral [[kaon]]s.

{{SubatomicParticle|strange B}}–{{SubatomicParticle|strange AntiB}} mixing was observed by the [[Collider Detector at Fermilab|CDF experiment]] at [[Fermilab]] in 2006 and by [[LHCb]] at [[CERN]] in 2011 and 2021.
[[File:B–Bbar_oscillation.png|thumb|B-bar oscillations detected via their respective [[D meson]] and [[Pion]] decays as seen by the LHCb in 2021. <math>\overline{B}_s^0\to D_s^-\pi^+</math> stands for the oscillation process <math>\overline{B}_s^0\to B_s^0\to D_s^-\pi^+</math>.]]

== Excess of matter over antimatter ==
{{main|B-factory}}

The Standard Model predicts that regular matter {{nobr|[[strange B meson|{{SubatomicParticle|strange B}} mesons]]}} are slightly favored in these oscillations over their antimatter counterpart, making strange B&nbsp;mesons of special [[LHCb#Physics goals|interest]] to particle physicists. The observation of the {{SubatomicParticle|B}}–{{SubatomicParticle|antiB}} mixing phenomena led physicists to propose the construction of the so-named [[B-factory|"B&nbsp;factories"]] in the early 1990s. They realized that a precise {{SubatomicParticle|B}}–{{SubatomicParticle|antiB}} oscillation measure could pin down the [[unitarity triangle]] and perhaps explain the [[baryon asymmetry|excess of matter over antimatter]] in the universe. To this end construction began on two "B&nbsp;factories" in the late nineties, one at the [[Stanford Linear Accelerator Center]] (SLAC) in [[California]] and one at [[KEK]] in [[Japan]].
[[File:B–Bbar oscillation Feynmandiagram.png|thumb|The oscillations are mediated by the [[W and Z bosons|W&nbsp;boson]] and the [[top quark]]; being heavier than the {{SubatomicParticle|strange B}}–{{SubatomicParticle|strange antiB}} mesons, they act as short lived [[Virtual particle|virtual particles]]]]

These B&nbsp;factories, [[BaBar Experiment|BaBar]] and [[Belle Experiment|Belle]], were set at the [[Upsilon meson|{{SubatomicParticle|Upsilon}}(4S)]] [[Resonance (particle)|resonance]] which is just above the threshold for decay into two B&nbsp;mesons.

On 14&nbsp;May 2010, physicists at the [[Fermilab|Fermi National Accelerator Laboratory]] reported that the oscillations decayed into matter 1% [[CP Violation#Direct CP violation|more often than into antimatter]], which may help explain the abundance of matter over antimatter in the observed Universe.<ref>{{cite news |title=A new clue to explain existence |date=2010-05-18 |newspaper=[[The New York Times]] |url=https://www.nytimes.com/2010/05/18/science/space/18cosmos.html?src=me&ref=general}}</ref> However, more recent results at [[LHCb]] in 2011, 2012, and 2021 with larger data samples have demonstrated no significant deviation from the Standard Model prediction of very nearly zero asymmetry.<ref>{{cite news |title=LHCb detector causes trouble for supersymmetry theory |date=29 August 2011 |website=[[Ars Technica]] |url=https://arstechnica.com/science/news/2011/08/lhcb-detector-causes-trouble-for-supersymmetry.ars}}</ref><ref>{{cite journal  |last1=Aaij |first1=R. |collaboration=LHCb collaboration |display-authors=etal |year=2014 |title=Measurement of the flavour-specific ''CP''-violating asymmetry a{{su|p=s|b=sl}} in B{{su|p=0|b=s}} decays |journal=[[Physics Letters B]] |volume=728 |issue= |pages=607–615 |doi=10.1016/j.physletb.2013.12.030 |doi-access=free |bibcode=2014PhLB..728..607A |arxiv=1308.1048 |s2cid=73647030 }}</ref><ref>{{cite journal |last1=Aaij |first1=R. |last2=Beteta| first2=C. Abellán |last3=Ackernley |first3=T. |last4=Adeva |first4=B. |last5=Adinolfi |first5=M. |last6=Afsharnia |first6=H. |last7=Aidala|first7=C.A. |last8=Aiola |first8=S. |last9=Ajaltouni |first9=Z. |last10=Akar |first10=S. |last11=Albrecht |first11=J. |display-authors=6 |date=2022-01-06 |df=dmy-all |title= Precise determination of the B{{su|p=0|b=s}}–{{overline|B{{su|p=0|b=s}}}} oscillation frequency |journal=[[Nature Physics]] |lang=en |volume=18 |issue= |pages=1–5 |arxiv=2104.04421 |doi=10.1038/s41567-021-01394-x |doi-access=free |s2cid=245809087 |issn=1745-2481 }}</ref>

==See also==
{{div col |colwidth=8em}}
* [[Baryogenesis]]
* [[CP Violation]]
* [[Kaon]]
* [[Neutral particle oscillation]]
* [[Strange B meson]]
{{div col end}}

==References==
{{reflist|25em}}

==Further reading==
<!-- abysmally slovenly citation ---
* [http://inspirehep.net/search?p=PHLTA,B192,245 Paper describing the discovery of B-meson mixing by the ARGUS Collaboration]
 --- dead link -->

* {{cite journal
 |last1=Albrecht |first1=H.
 |collaboration=ARGUS collaboration
 |display-authors=etal
 |year=1987
 |title=Observation of B{{su|p=0}}–B{{su|p=0}} mixing
 |journal=Physics Letters B
 |volume=192 |issue=1–2 |pages=245–252
 |doi=10.1016/0370-2693(87)91177-4
 |url=https://www.sciencedirect.com/science/article/abs/pii/0370269387911774
}} — paper describing the discovery of B-meson mixing by the ARGUS collaboration
* {{cite press release
 |title=Fermilab's CDF scientists present a precision measurement of a subtle dance between matter and antimatter
 |date=11 April 2006
 |publisher=[[Fermilab]]
 |url=http://www.fnal.gov/pub/presspass/press_releases/CDF_04-11-06.html
}}
* {{cite press release
 |title=Fermilab's CDF scientists make it official: They have discovered the quick-change behavior of the B-sub-s meson, which switches between matter and antimatter 3&nbsp;trillion times a second
 |date=25 September 2006
 |publisher=[[Fermilab]]
 |url=http://www.fnal.gov/pub/presspass/press_releases/CDF_meson.html
}} — announcement of the 5&nbsp;sigma discovery

==External links==
* [http://www-public.slac.stanford.edu/babar/ BaBar Public Homepage]
* [http://belle.kek.jp/ Belle Public Homepage]

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[[Category:B physics]]
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