The ${\bar c} c$ purity of $ψ(3770)$ and $ψ'$ challenged

Abstract

It is suggested that the resonance $ψ(3770)$ may contain a sizeable ($O(10%)$ in terms of the probability weight factor) four-quark component with the up- and down- quarks and antiquarks in addition to the $c {\bar c}$ pair, which component in itself has a substantial part with the isospin I=1. Furthermore such four-quark part of the wave function should also affect the properties of the $ψ'$ charmonium resonance through the $ψ(3770) - ψ'$ mixing previously considered in the literature. It is argued that an admixture of extra light quark pairs can explain a possible discrepancy between the theoretical expectations and the recent data on the non-$D {\bar D}$ decay width of the $ψ(3770)$ and the ratio of the yield of charged and neutral $D$ meson pairs in its decays, as well as on the extra rate of the $ψ'$ direct decay into light hadrons and the rate of the decay $ψ' \to π^0 J/ψ$. It is further argued that the suggested four-quark component of the wave function of the $ψ(3770)$ should give rise to a measurable rate of the decays $ψ(3770) \to ηJ/ψ$ and $ψ(3770) \to π^0 J/ψ$.