Near-threshold $D\bar{D}$ spectroscopy and observation of a new charmonium state

Using proton-proton collision data, corresponding to an integrated luminosity of 9$f{b}^{-1}$, collected with the~LHCb detector between 2011 and 2018, a new narrow charmonium state, the $X(3842)$ resonance, is observed in the decay modes $X(3842)\to D^0{\bar{D}}^0$ and $X(3842)\to D^{+}{D}^{-}$. The mass and the natural width of this state are measured to be \begin{eqnarray*} m_{X(3842)} & = & 3842.71 \pm 0.16 \pm 0.12 MeV/c^2,, \Gamma_{X(3842)} & = & 2.79 \pm 0.51 \pm 0.35 MeV,, \end{eqnarray*} where the first uncertainty is statistical and the~second is systematic. The observed mass and narrow natural width suggest the~interpretation of the new state as the~unobserved spin\nobreakdash-3 ${\psi }_3\left(1^3{\mathrm{D}}_3\right)$ charmonium state. In addition, prompt hadroproduction of the $\psi (3770)$~and ${\chi }_{c2}(3930)$ states is observed for the first time, and the parameters of these~states are measured to be \begin{eqnarray*} m_{\psi(3770)} & = & 3778.1 \pm 0.7 \pm 0.6 MeV/c^2,, m_{\chi_{c2}(3930)} & = & 3921.9 \pm 0.6 \pm 0.2 MeV/c^2,, \Gamma_{\chi_{c2}(3930)} & = &36.6 \pm 1.9 \pm 0.9 MeV,, \end{eqnarray*} where the first uncertainty is statistical and the~second is systematic.