The meson has spin

PHYSICS · Subjective · Fermi University Physics · Particle Physics & Quantum Fields · Particles, interactions and experiment · Particles, interactions and experiment

Symmetry and Flavour, Ch Resonances: the relativistic Breit-Wigner, unitarity and the Z line shape

Problem

The ϕ(1020)\phi(1020) meson has spin J=1J=1, mass M=1019.461 MeVM=1019.461\,\mathrm{MeV}, total width Γ=4.249 MeV\Gamma=4.249\,\mathrm{MeV}, branching ratio to e+e−e^+e^- of Bee=2.954×10−4\mathcal{B}_{ee}=2.954\times10^{-4} and branching ratio to K+K−K^+K^- of BK+K−=49.2%\mathcal{B}_{K^+K^-}=49.2\% (PDG 2024). Using the peak relativistic Breit-Wigner cross section for a J=1J=1 state formed in e+e−e^+e^- collisions, σf0=12π ΓeeΓfM2Γ2\sigma^0_f = \dfrac{12\pi\,\Gamma_{ee}\Gamma_f}{M^2\Gamma^2}, predict the peak cross section for e+e−→ϕ(1020)→K+K−e^+e^- \to \phi(1020) \to K^+K^-, in nb.

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