Wave-packet Effects: a Solution for Isospin Anomalies in Vector-Meson Decay

There is a long-standing anomaly in the ratio of the decay width for ψ (3770)→ D^0D^0 to that for ψ (3770)→ D^+D^- at the level of 9.5 σ . A similar anomaly exists for the ratio of ϕ (1020)→ K_L^0K_S^0 to ϕ (1020)→ K^+K^- at 2.1 σ . In this study, we reassess the anomaly through the lens of a Gaussian wave-packet formalism. Our comprehensive calculations include the localization of the overlap of the wave packets near the mass thresholds and the composite nature of the initial-state vector mesons. The results align within a ∼ 1 σ confidence level with the Particle Data Group’s central values for a physically reasonable value of the form-factor parameter, indicating a resolution to these anomalies. We also check the deviation of a wave-packet resonance from the Briet–Wigner shape and find that wide ranges of the wave-packet size are consistent with the experimental data.