Probing the nature of the $\ddot{I}{‡}_{c1}(3872)$ state using radiative decays

Abstract

The radiative decays $\ddot{I}{‡}_{c1}(3872)\to \ddot{I}ˆ(2S){\hat{I}}^3$ and $\ddot{I}{‡}_{c1}(3872)\to J/\ddot{I}ˆ{\hat{I}}^3$ are used to probe the~nature of the~$\ddot{I}{‡}_{c1}(3872)$ state using proton-proton collision data collected with the LHCb detector, corresponding to an~integrated luminosity of~9fb${}^{-1}$. Using the~$B^{+}\to \ddot{I}{‡}_{c1}(3872)K^{+}$decay, the $\ddot{I}{‡}_{c1}(3872)\to \ddot{I}ˆ(2S){\hat{I}}^3$ process is observed for the first time and the ratio of its partial width to that of the $\ddot{I}{‡}_{c1}(3872)\to J/\ddot{I}ˆ{\hat{I}}^3$ decay is measured to be $$\frac{\hat{I}{“}_{\ddot{I}{‡}_{c1}(3872)\to \ddot{I}ˆ(2S){\hat{I}}^3}}{\hat{I}{“}_{\ddot{I}{‡}_{c1}(3872)\to J/\ddot{I}ˆ{\hat{I}}^3}}=1.67\pm 0.21\pm 0.12\pm 0.04,$$ where the first uncertainty is statistical, the second systematic and the third is due to the uncertainties on the branching fractions of the $\ddot{I}ˆ(2S)$ and $J/\ddot{I}ˆ$ mesons. The measured ratio makes the interpretation of the $\ddot{I}{‡}_{c1}(3872)$ state as a~pure $D^0{\bar{D}}^{\ast 0}+{\bar{D}}^0{D}^{\ast 0}$ molecule questionable and strongly indicates a sizeable compact charmonium or tetraquark component within the $\ddot{I}{‡}_{c1}(3872)$ state.

31 pages, 2 figures. All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2024-015.html (LHCb public pages)