${\chi }_{c0}(3915)$ as the lightest $c\overline{c}s\overline{s}$ state

The state ${\chi }_{c0}(3915)$ has recently been demoted by the Particle Data Group from its previous status as the conventional $c\overline{c}$ $2^3{P}_0$ state, largely due to the absence of expected $D\overline{D}$ decays. We propose that ${\chi }_{c0}(3915)$ is actually the lightest $c\overline{c}s\overline{s}$ state, and calculate the spectrum of such states using the diquark model, identifying many of the observed charmoniumlike states that lack open-charm decay modes as $c\overline{c}s\overline{s}$. Among other results, we argue that $Y(4140)$ is a $J^{PC}=1^{++}$ $c\overline{c}s\overline{s}$ state that has been not been seen in two-photon fusion largely as a consequence of the Landau-Yang theorem.