Study of the doubly charmed tetraquark $T_{cc}^{+}$

Abstract

An exotic narrow state in the $D^0{D}^0\ddot{I}{€}^{+}$ mass spectrum just below the $D^{\ast +}{D}^0$ mass threshold is studied using a data set corresponding to an integrated luminosity of 9 fb${}^{-1}$ acquired with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The state is consistent with the ground isoscalar $T_{cc}^{+}$ tetraquark with a quark content of $cc\bar{u}\bar{d}$ and spin-parity quantum numbers ${\mathrm{J}}^{\mathrm{P}}=1^{+}$. Study of the $DD$ mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell $D^{\ast +}$ mesons is confirmed by the $D^0\ddot{I}{€}^{+}$ mass distribution. The mass of the resonance and its coupling to the $D^{\ast }D$ system are analysed. Resonance parameters including the pole position, scattering length, effective range and compositeness are measured to reveal important information about the nature of the $T_{cc}^{+}$ state. In addition, an unexpected dependence of the production rate on track multiplicity is observed.

All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2021-032.html