The $\bar{c}c$ purity of $\psi (3770)$ and ${\psi }^{\mathrm{\prime }}$ challenged

It is suggested that the resonance $\psi (3770)$ 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 ${\psi }^{\mathrm{\prime }}$ charmonium resonance through the $\psi (3770)-{\psi }^{\mathrm{\prime }}$ 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 $\psi (3770)$ 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 ${\psi }^{\mathrm{\prime }}$ direct decay into light hadrons and the rate of the decay ${\psi }^{\mathrm{\prime }}\to {\pi }^{0}J\mathrm{/}\psi$. It is further argued that the suggested four-quark component of the wave function of the $\psi (3770)$ should give rise to a measurable rate of the decays $\psi (3770)\to \eta J\mathrm{/}\psi$ and $\psi (3770)\to {\pi }^{0}J\mathrm{/}\psi$.