The X(3872) is an exotic meson candidate with a mass of 3871.68 MeV/c2[1] which does not fit into the quark model because of its quantum numbers. It was first discovered in 2003 by the Belle experiment[2] in Japan and later confirmed by several other experimental collaborations. Several theories have been proposed for its nature,[3] such as a mesonic molecule or a diquark-antidiquark pair (tetraquark).
The quantum numbers of X(3872) have been determined by the LHCb experiment at CERN in March 2013. The values for JPC are 1++.[4] The first evidence of X(3872) production in the quark–gluon plasma have been reported by the CMS experiment at CERN in January 2022.[5]
Original source: https://en.wikipedia.org/wiki/X(3872).
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