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

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 $\mathrm{X}(3842)\to {D}^0{\overline{D}}^0$ and X(3842) → D⁺D⁻. The mass and the natural width of this state are measured to be

$$ \begin{array}{l}{m}_{X(3842)}=3842.71\pm 0.16\pm 0.12\ MeV/{c}^2,\hfill \\ {}{\varGamma}_{X(3842)}=2.79\pm 0.51\pm 0.35\ MeV,\hfill \end{array} $$

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-3 ψ₃ 1³D₃) charmonium state.

In addition, prompt hadroproduction of the ψ(3770) and χ₂(3930) states is observed for the first time, and the parameters of these states are measured to be

$$ \begin{array}{l}{m}_{\psi (3770)}=3778.1\pm 0.7\pm 0.6\ MeV/{c}^2,\hfill \\ {}{m}_{\chi_2(3930)}=3921.9\pm 0.6\pm 0.2\ MeV/{c}^2,\hfill \\ {}{\varGamma}_{\chi_2(3930)}=36.6 \pm 1.9 \pm 0.9\ MeV,\hfill \end{array} $$

where the first uncertainty is statistical and the second is systematic.