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A tetraquark, in particle physics, is an exotic meson composed of four valence quarks. In principle, a tetraquark state may be allowed in quantum chromodynamics, the modern theory of strong interactions. Any established tetraquark state would be an example of an exotic hadron which lies outside the quark model classification. ==History== In 2003 a particle temporarily called X(3872), by the Belle experiment in Japan, was proposed to be a tetraquark candidate,〔 〕 as originally theorized.〔 〕 The name X is a temporary name, indicating that there are still some questions about its properties to be tested. The number following is the mass of the particle in . In 2004, the DsJ(2632) state seen in Fermilab's SELEX was suggested as a possible tetraquark candidate. In 2007, Belle announced the observation of the Z(4430) state, a tetraquark candidate. In 2014, the Large Hadron Collider experiment LHCb confirmed this resonance with a significance of over 13.9σ. There are also indications that the Y(4660), also discovered by Belle in 2007, could be a tetraquark state.〔 〕 In 2009, Fermilab announced that they have discovered a particle temporarily called Y(4140), which may also be a tetraquark. In 2010, two physicists from DESY and a physicist from Quaid-i-Azam University re-analyzed former experimental data and announced that, in connection with the (a form of bottomonium), a well-defined tetraquark resonance exists.〔(【引用サイトリンク】title=Evidence grows for tetraquarks )〕〔 〕 In June 2013, two independent groups reported on Zc(3900). 〔 〕 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「Tetraquark」の詳細全文を読む スポンサード リンク
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