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A pentaquark is a subatomic particle consisting of four quarks and one antiquark bound together. As quarks have a baryon number of +, and antiquarks of −, the pentaquark would have a total baryon number of 1, and thus would be a baryon. Further, because it has five quarks instead of the usual three found in regular baryons (aka 'triquarks'), it would be classified as an exotic baryon. The name pentaquark was coined by Harry J. Lipkin in 1987,〔 〕 however, the possibility of five-quark particles was identified as early as 1964 when Murray Gell-Mann first postulated the existence of quarks.〔 decays |url=http://lhcb-public.web.cern.ch/lhcb-public/Welcome.html#Penta |publisher=CERN/LHCb |accessdate=2015-07-14 }}〕 Although predicted for decades, pentaquarks have proved surprisingly difficult to discover and some physicists were beginning to suspect that an unknown law of nature prevented their production.〔 〕 The first claim of pentaquark discovery was recorded at LEPS in Japan in 2003, and several experiments in the mid-2000s also reported discoveries of other pentaquark states.〔 〕 Others were not able to replicate the LEPS results, however, and the other pentaquark discoveries were not accepted because of poor data and statistical analysis.〔See p. 1124 in 〕 On 13 July 2015, the LHCb collaboration at CERN reported results consistent with pentaquark states in the decay of bottom Lambda baryons ().〔 decays |journal=Physical Review Letters |volume=115 |issue=7 |doi=10.1103/PhysRevLett.115.072001 }}〕 Outside of particle physics laboratories pentaquarks also could be produced naturally by supernovae as part of the process of forming a neutron star.〔 〕 The scientific study of pentaquarks might offer insights into how these stars form, as well as allowing more thorough study of particle interactions and the strong force. ==Background== (詳細はquark is a type of elementary particle that has mass, electric charge, and colour charge, as well as an additional property called flavour, which describes what type of quark it is (up, down, strange, charm, top, or bottom). Due to an effect known as colour confinement, quarks are never seen on their own. Instead, they form composite particles known as hadrons so that their colour charges cancel out. Hadrons made of one quark and one antiquark are known as mesons, while those made of three quarks are known as baryons. These 'regular' hadrons are well documented and characterized, however, there is nothing in theory to prevent quarks from forming 'exotic' hadrons such as tetraquarks with two quarks and two antiquarks, or pentaquarks with four quarks and one antiquark.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「pentaquark」の詳細全文を読む スポンサード リンク
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