X(3872)

The X(3872) is an exotic meson candidate with a mass of 3871.68 MeV/c^2[1] which does not fit into the quark model. 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 J^PC 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]

See also

• Meson
• XYZ particle
• Y(4140)
• Z(4430)
• Zc(3900)