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

## TL;DR

This paper reports the discovery of a new narrow charmonium state, X(3842), and measures properties of known states, providing insights into charmonium spectroscopy near the Dar{D} threshold using LHCb proton-proton collision data.

## Contribution

First observation of the X(3842) state as a potential spin-3 charmonium, with precise measurements of its mass and width, and first-time measurements of prompt production of ψ(3770) and χ_{c2}(3930).

## Key findings

- Discovery of X(3842) with mass 3842.71 MeV/c^2 and width 2.79 MeV.
- First observation of prompt production of ψ(3770) and χ_{c2}(3930).
- Measured parameters of ψ(3770) and χ_{c2}(3930).

## Abstract

Using proton-proton collision data, corresponding to an integrated luminosity of 9$fb^{-1}$, collected with the~LHCb detector between 2011 and 2018, a new narrow charmonium state, the $X(3842)$ resonance, is observed in the decay modes $X(3842)\rightarrow D^0\bar{D}^0$ and $X(3842)\rightarrow D^+D^-$. 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 $\psi_3\mathrm{\left(1^3D_3\right)}$ 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.