10.06.2024Observation of J/ψ decaying to four muons

The J/ψ meson has played an important role in establishing quantum chromodynamics (QCD) as the theory that describes the strong force that binds quarks and gluons inside hadrons and, indirectly, protons and neutrons in atomic nuclei and can also be used to probe quantum electrodynamics (QED). It is composed of a charm quark and a charm antiquark and quickly decays into more stable particles, such as muons.
The CMS experiment has observed, for the first time ever, the decay of the J/ψ meson into four muons (J/ψ → μ⁺μ⁻μ⁺μ⁻).

CMS publication

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