| 词条 | Xi baryon | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 释义 |
The Xi baryons or cascade particles are a family of subatomic hadron particles which have the symbol Ξ and may have an electric charge (Q) of +2 e, +1 e, 0, or −1 e, where e is the elementary charge. Like all conventional baryons, they contain three quarks. Xi baryons, in particular, contain one up or down quark plus two more massive quarks: either strange, charm or bottom. They are historically called the cascade particles because of their unstable state; they decay rapidly into lighter particles through a chain of decays.[1] The first discovery of a charged Xi baryon was in cosmic ray experiments by the Manchester group in 1952.[2] The first discovery of the neutral Xi particle was at Lawrence Berkeley Laboratory in 1959.[3] It was also observed as a daughter product from the decay of the omega baryon ({{SubatomicParticle|Omega-}}) observed at Brookhaven National Laboratory in 1964.[1] The Xi spectrum is important to nonperturbative quantum chromodynamics (QCD), such as Lattice QCD.{{why|date=December 2016}} HistoryThe {{SubatomicParticle|Bottom Xi-}} particle is also known as the cascade B particle and contains quarks from all three families. It was discovered by D0 and CDF experiments at Fermilab. The discovery was announced on 12 June 2007. It was the first known particle made of quarks from all three quark generations – namely, a down quark, a strange quark, and a bottom quark. The D0 and CDF collaborations reported the consistent masses of the new state. The Particle Data Group world average mass is {{val|5.7924|0.0030|u=GeV/c2}}. Unless specified, the non-up/down quark content of Xi baryons is strange (i.e. there is one up or down quark and two strange quarks). However a {{SubatomicParticle|Bottom Xi0}} contains one up, one strange, and one bottom quark, while a {{SubatomicParticle|Double bottom xi0}} contains one up and two bottom quarks. In 2012, the CMS experiment at the Large Hadron Collider detected a {{SubatomicParticle|bottom xi*0}} baryon (reported mass {{val|5945|2.8|u=MeV/c2}}).[4][5] The LHCb experiment at CERN discovered two new Xi baryons in 2014: {{Subatomic particle|bottom xi'-}} and {{Subatomic particle|bottom xi*-}} [6]. In 2017, the LHCb researchers reported yet another Xi baryon: the double charmed {{SubatomicParticle|Double charmed Xi++}} baryon, consisting of two heavy charm quarks and one up quark. The mass of {{SubatomicParticle|Double charmed Xi++}} is about 3.8 times that of a proton.[7][8] List of Xi baryons
See also
References1. ^1 {{cite web |author=R. Nave |date= |title=The Xi Baryon |url=http://hyperphysics.phy-astr.gsu.edu/hbase/particles/xi.html |website=HyperPhysics |accessdate=4 April 2013}} 2. ^{{cite journal |author=R. Armenteros|year=1952 |title=The properties of charged V-particles |journal=Philosophical Magazine |volume=43 |issue=341 |page=597 |doi=10.1080/14786440608520216|display-authors=etal}} 3. ^{{cite journal |author=L. W. Alvarez|year=1959 |title=Neutral Cascade Hyperon Event |journal=Physical Review Letters |volume=2 |issue=5 |page=215 |bibcode=1959PhRvL...2..215A |doi=10.1103/PhysRevLett.2.215 |display-authors=etal|url=http://www.escholarship.org/uc/item/2gs1j865 }} 4. ^{{cite web |author=C. Simpson |date=28 April 2013 |title=New Particle Discovered with 'Higgs Boson' Machine |url=http://www.theatlanticwire.com/technology/2012/04/new-particle-discovered-higgs-boson-machine/51688/ |website=The Atlantic Wire |accessdate=2013-04-04}} 5. ^{{cite journal |author=S. Chatrchyan |display-authors=etal |collaboration=CMS Collaboration |year=2012 |title=Observation of an excite excited Ξb baryon |journal=Physical Review Letters |volume=108 |issue=25 |pages=252002 |arxiv=1204.5955 |bibcode=2012PhRvL.108y2002C |doi=10.1103/PhysRevLett.108.252002 |pmid=23004588}} 6. ^{{Cite news|url = http://press.web.cern.ch/press-releases/2014/11/lhcb-experiment-observes-two-new-baryon-particles-never-seen|title = LHCb experiment observes two new baryon particles never seen before|date = 19 Nov 2014|work = |accessdate = }} 7. ^{{Cite press release|url = https://press.cern/press-releases/2017/07/lhcb-experiment-charmed-announce-observation-new-particle-two-heavy-quarks|title = The LHCb experiment is charmed to announce observation of a new particle with two heavy quarks|date = 2017-07-06|publisher = CERN |accessdate = 2017-07-06}} 8. ^{{Cite news|url=https://www.nytimes.com/2017/07/06/science/cern-quarks-charm-baryon.html|title=CERN Physicists Find a Particle With a Double Dose of Charm|last=Chang|first=Kenneth|date=2017-07-06|newspaper=The New York Times|access-date=2017-07-08|language=en-US|issn=0362-4331}} 9. ^1 {{cite journal |author=V. Abazov et al. (D0 Collaboration) |year=2007 |title=Direct observation of the strange b baryon {{SubatomicParticle|Bottom Xi-}} |journal=Physical Review Letters |volume=99 |issue=5 |pages=52001 |arxiv=0706.1690 |bibcode=2007PhRvL..99e2001A |doi=10.1103/PhysRevLett.99.052001 |pmid=17930744 |hdl=10211.3/194385 }} 10. ^{{cite press |date=13 June 2007 |title=Fermilab physicists discover "triple-scoop" baryon |url=http://www.fnal.gov/pub/presspass/press_releases/Dzero_baryon.html |publisher=Fermilab |accessdate=2007-06-14}} 11. ^{{cite press |date=25 June 2007 |title=Back-to-Back b Baryons in Batavia |url=http://www.fnal.gov/pub/presspass/press_releases/backtobackBaryons.html |publisher=Fermilab |accessdate=2007-06-25}} 12. ^1 {{cite journal |author=T. Aaltonen et al. (CDF Collaboration) |year=2007 |title=Observation and mass measurement of the baryon Xi(b)- |journal=Physical Review Letters |volume=99 |issue=5 |pages=52002 |arxiv=0707.0589 |bibcode=2007PhRvL..99e2002A |doi=10.1103/PhysRevLett.99.052002|pmid=17930745 |hdl=10261/8530 }} 13. ^{{cite journal |author=W.-M. Yao et al. (Particle Data Group) |year=2006 |title=Particle listings – Xi{{sup|0}} |url=http://pdg.lbl.gov/2007/listings/s023.pdf |journal=Journal of Physics G |volume=33 |issue=1 |pages=1–1232 |bibcode= 2006JPhG...33....1Y |doi= 10.1088/0954-3899/33/1/001|arxiv = astro-ph/0601168 }} 14. ^{{cite journal |author=W.-M. Yao et al. (Particle Data Group) |year=2006 |title=Particle listings – Xi{{sup|−}} |url=http://pdg.lbl.gov/2007/listings/s022.pdf |journal=Journal of Physics G |volume=33 |issue=1 |pages=1–1232 |bibcode= 2006JPhG...33....1Y |doi= 10.1088/0954-3899/33/1/001|arxiv = astro-ph/0601168 }} 15. ^1 {{cite journal |author=W.-M. Yao et al. (Particle Data Group) |year=2006 |title=Particle Listings – Xi(1530) |url=http://pdg.lbl.gov/2007/listings/b049.pdf |journal=Journal of Physics G |volume=33 |issue=1 |pages=1–1232 |doi= 10.1088/0954-3899/33/1/001|arxiv = astro-ph/0601168 |bibcode = 2006JPhG...33....1Y }} 16. ^1 2 3 {{cite journal |author=W.-M. Yao et al. (Particle Data Group) |year=2006 |title=Particle listings – Charmed baryons |journal=Journal of Physics G |url=http://pdg.lbl.gov/2007/tables/bxxxcharm.pdf |volume=33 |issue=1 |pages=1–1232 |arxiv= astro-ph/0601168 |bibcode= 2006JPhG...33....1Y |doi= 10.1088/0954-3899/33/1/001}} 17. ^{{Cite news|url = https://press.cern/press-releases/2017/07/lhcb-experiment-charmed-announce-observation-new-particle-two-heavy-quarks|title = The LHCb experiment is charmed to announce observation of a new particle with two heavy quarks|date = 6 Jul 2017|work = |accessdate = }} 18. ^https://home.cern/about/updates/2018/05/long-live-doubly-charmed-particle 19. ^{{cite journal |author=W.-M. Yao et al. (Particle Data Group) |year=2006 |title=Particle listings – Ξ{{su|p=+|b=cc}} |url=http://pdg.lbl.gov/2007/listings/s065.pdf |journal=Journal of Physics G |volume=33 |issue=1 |page=1 |arxiv= astro-ph/0601168 |bibcode= 2006JPhG...33....1Y |doi= 10.1088/0954-3899/33/1/001}} 20. ^1 {{cite journal |author=W.-M. Yao et al. (Particle Data Group) |year=2006 |title=Particle listings – Xib |journal=Journal of Physics G |volume=33 |issue=1 |pages=1–1232 |url=http://pdg.lbl.gov/2007/listings/s060.pdf|arxiv = astro-ph/0601168 |bibcode = 2006JPhG...33....1Y |doi = 10.1088/0954-3899/33/1/001 }} 21. ^{{cite journal |author=T. Aaltonen et al. (CDF Collaboration) |year=2007 |title= Observation and mass measurement of the baryon {{SubatomicParticle|Bottom Xi-}} |journal=Physical Review Letters |volume=99 |issue=5 |pages=052002 |arxiv=0707.0589 |bibcode=2007PhRvL..99e2002A |doi=10.1103/PhysRevLett.99.052002|pmid=17930745 |hdl=10261/8530 }} 22. ^1 {{Cite journal|arxiv = 1411.4849|title = Observation of two new Ξ{{su|p=−|b=b}} baryon resonances|year = 2015|journal = Physical Review Letters|volume = 114|issue = 6|pages = 062004|doi =10.1103/PhysRevLett.114.062004 |pmid = 25723210|bibcode = 2015PhRvL.114f2004A|last1 = Aaij|first1 = R |displayauthors = etal |collaboration=LHCb Collaboration}} 23. ^{{Cite journal |arxiv = 1805.09418|last1 =Aaij|first1 = R. |collaboration=CMS Collaboration |display-authors=etal |title = Observation of a new Ξ{{su|b=b|p=−}} resonance|journal = Physical Review Letters|volume = 121|issue = 72002|pages = 072002|year = 2018|doi = 10.1103/PhysRevLett.121.072002|pmid = 30169090}} External links
2 : Baryons|Nuclear physics |
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