Reevaluating the $\psi (4160)$ Resonance Parameter Using $B^{+}\to K^{+}{\mu }^{+}{\mu }^{-}$ Data in the Context of Unquenched Charmonium Spectroscopy

A puzzling phenomenon, where the measured mass of the $\psi (4160)$ is pushed higher, presents a challenge to current theoretical models of hadron spectroscopy. This study suggests that the issue arises from analyses based on the outdated quenched charmonium spectrum. In the past two decades, the discovery of new hadronic states has emphasized the importance of the unquenched effect. Under the unquenched picture, six vector charmonium states-$\psi (4040)$, $\psi (4160)$, $\psi (4220)$, $\psi (4380)$, $\psi (4415)$, and $\psi (4500)$-are identified in the $4\sim 4.5$ GeV range, contrasting with the three states predicted in the quenched model. We reevaluate the resonance parameters of the $\psi (4160)$ using the di-muon invariant mass spectrum of $B^{+}\to K^{+}{\mu }^{+}{\mu }^{-}$ and unquenched charmonium spectroscopy. Our analysis finds the $\psi (4160)$ mass at $4145.76\pm 4.48$ MeV, indicating previous overestimations. This conclusion is supported by analyzing $e^{+}{e}^{-}\to D_s{\bar{D}}_s^{\ast }$. Our findings have significant implications for both hadron spectroscopy and search for new physics signals by $R_K$.