|
A pentaquark is a subatomic particle consisting of a group of five quarks (compared to three quarks in normal baryons and two in mesons), or more specifically four quarks and one anti-quark. Hence it has baryon number 1. It has therefore been assigned a new particle classification, called an exotic baryon. Several experiments since 2003 claim to have seen a pentaquark with a mass of about 1540 MeV, presumably composed of two up quarks, two down quarks and an anti-strange quark (). This is the minimal quark composition of an object with baryon number 1, and positive strangeness. 1974 discovery photograph of a possible charmed baryon, now identified as the Σc++ In particle physics, the quarks are subatomic particles thought to be elemental and indivisible. ...
In particle physics, the baryons are a family of subatomic particles including the proton and the neutron (collectively called nucleons), as well as a number of unstable, heavier particles (called hyperons). ...
In particle physics, a meson is a strongly interacting boson, that is, it is a hadron with integral spin. ...
In particle physics, the baryon number is an approximate conserved quantum number. ...
In particle physics, an exotic baryon is a baryon (a strongly interacting fermion) composed of more than three quarks. ...
Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ...
An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. ...
In particle physics, strangeness is the number of anti-strange quarks minus the number of strange quarks in a particle. ...
These five quarks are not, however, ordinary constituent quarks in the model that predicted the existence of the pentaquark. The `fourth' quark is seen as a higher density of states in the Dirac sea with negative energy, while the antiquark is a lower density of states with positive energy. This does not cost as much energy as the creation of a particle-hole excitation, therefore the pentaquark is lighter than the 2 GeV or so that would be predicted by other constituent quark models. The Dirac sea is a theoretical model of the vacuum as an infinite sea of particles possessing negative energy. ...
The Dirac sea is a theoretical model of the vacuum as an infinite sea of particles possessing negative energy. ...
An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. ...
History The existence of pentaquarks was originally hypothesized by Maxim Polyakov, Dmitri Diakonov, and Victor Petrov at the Petersburg Nuclear Physics Institute in Russia in 1997, but their predictions were met with skepticism. Nevertheless, the existence of pentaquarks was first reported in July 2003 from experiments run by Takashi Nakano of Osaka University, Japan, and by Ken Hicks at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) in Newport News, Virginia. Their experiments caused a high-energy gamma ray to interact with a neutron, creating a meson and a pentaquark. However, the pentaquark only survived for about 10-20 seconds before decaying into a meson and a neutron. 1997 is a common year starting on Wednesday of the Gregorian calendar. ...
July is the seventh month of the year in the Gregorian Calendar and one of seven Gregorian months with the length of 31 days. ...
2003 is a common year starting on Wednesday of the Gregorian calendar. ...
Osaka University (大阪大学 Ōsaka Daigaku; abbreviated to 阪大 Handai) is a public coeducational research university in Suita, Osaka, Japan. ...
Newport News, Hampton, Portsmouth and Norfolk, Virginia from space, July 1996 Newport News is an independent city located in Virginia. ...
State nickname: Old Dominion Other U.S. States Capital Richmond Largest city Virginia Beach Governor Mark R. Warner Official languages English Area 110,862 km² (35th) - Land 102,642 km² - Water 8,220 km² (7. ...
This article is about electromagnetic radiation. ...
Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ...
To help compare orders of magnitude of different times this page lists times between 10-20 seconds and 10-19 seconds (10 zeptoseconds and 100 zeptoseconds) See also times of other orders of magnitude. ...
Radioactive decay is the set of various processes by which unstable atomic nuclei (nuclides) emit subatomic particles. ...
In particle physics, a meson is a strongly interacting boson, that is, it is a hadron with integral spin. ...
Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ...
But the existence of the pentaquark was highly disputed. In order to clear up the issue, the CLAS collaboration set up an experiment at Jefferson Lab with the purpose of searching for pentaquarks. Results were entirely serendipitous. Serendipity is finding something unexpected and useful while searching for something else entirely. ...
The CLAS collaboration again hunted in 2005 by accelerating energetic photons into liquid hydrogen. Previously a German team, SAPHIR, produced postive results, but CLAS produced a result 50x more precise than SAPHIR's by collecting 10x the data at the expected energy range of the decay particles. CLAS team member Raffaella De Vita, of Italy's National Institute of Nuclear Physics, presented results on April 17th 2005 at a meeting of the American Physical Society in Tampa, Florida, USA, and showed that CLAS was unable to reproduce the previous results—no evidence for pentaquarks was seen. More results from CLAS at Jefferson Lab are expected later in 2005.
It is worth noting that the experiments that fail to see the pentaquark are at higher energy where the meson exchange production mechanism dies out in favor of flavor neutral gluon exchange; the latter is doubly suppressed by the OZI rule. Therefore the upper limits on the production rate of the pentaquark determined from the null results of some experiments do not necessarily disprove its existence. In particle physics, a meson is a strongly interacting boson, that is, it is a hadron with integral spin. ...
In particle physics, flavor is a property of a fermion that identifies it, a label that specifies the name of the particle. ...
In particle physics, gluons mediate strong interactions of quarks in quantum chromodynamics. ...
See also List of particles in particle physics. ...
In particle physics, a hadron is a subatomic particle which experiences the strong nuclear force. ...
In particle physics, a hadron is a subatomic particle which experiences the strong nuclear force. ...
The quark model is a classification scheme for hadrons in terms of their valence quarks, ie, the quarks (and antiquarks) which give rise to the quantum numbers of the hadrons. ...
External links - Behold the Pentaquark (BBC News) (http://news.bbc.co.uk/1/low/sci/tech/3034754.stm)
- Pentaquark discovery confounds sceptics (New Scientist) (http://www.newscientist.com/news/news.jsp?id=ns99993903)
- Pentaquark hunt draws blanks (http://www.newscientist.com/article.ns?id=dn7287&feedId=online-news_rss20), Is It or Isn't It? (http://www.spacedaily.com/news/physics-05t.html), (mirror) (http://www.physorg.com/news3815.html)
- Physicists Find Evidence for an Exotic Baryon (Ohio University) (http://www.phy.ohiou.edu/~hicks/thplus.htm)
- hep-ex/0412048: An Experimental Review of the Θ+ Pentaquark (http://arxiv.org/abs/hep-ex/0412048)
- hep-ph/0401115: Prospects for Pentaquark Production at Meson Factories (http://arxiv.org/abs/hep-ph/0401115)
- hep-ph/0404019: An Attempt to Study Pentaquark Baryons in String Theory (http://arxiv.org/abs/hep-ph/0404019)
- Relativistic Mean Field Approximation to Baryons (http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+key+6181597)
- News article published in Nature (April 2005). (http://www.nature.com/news/2005/050418/full/050418-1.html)
|
Feeds |
Contact