Tetraquark

In particle physics, a tetraquark is an exotic meson composed of four valence quarks. A tetraquark state has long been suspected to be allowed by quantum chromodynamics,^[1] the modern theory of strong interactions. A tetraquark state is an example of an exotic hadron which lies outside the conventional quark model classification. A number of different types of tetraquark have been observed.^[2]^[3]

^ U. Kulshreshtha; D. S. Kulshreshtha; J. P. Vary (2015). "Hamiltonian, path integral and BRST formulations of large N scalar QCD₂ on the light-front and spontaneous symmetry breaking". European Physical Journal C. 75 (4): 174. arXiv:1503.06177. Bibcode:2015EPJC...75..174K. doi:10.1140/epjc/s10052-015-3377-x. S2CID 119102254.
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