A combined amplitude analysis is performed for the decays $B^0 \rightarrow \overline{ D}^0 D^+_s\pi^-$ and $B^+\rightarrow D^- D^+_s\pi^+$, which are related by isospin symmetry. The analysis is based on data collected by the LHCb detector in proton-proton collisions at center-of-mass energies of 7, 8 and 13$\,\rm{ TeV}$. The full data sample corresponds to an integrated luminosity of 9$\,\rm{ fb^{ -1}}$. Two new resonant states with masses of $2.908\pm0.011\pm0.020\,\rm{ GeV}$ and widths of $0.136\pm0.023\pm0.011\,\rm{ GeV}$ are observed, which decay to $D^+_s\pi^+$ and $D^+_s\pi^-$ respectively. The former state indicates the first observation of a doubly charged open-charm tetraquark state with minimal quark content $[c\bar{ s}u\bar{ d}]$, and the latter state is a neutral tetraquark composed of $[c\bar{ s}\bar{ u}d]$ quarks. Both states are found to have spin-parity $0^+$, and their resonant parameters are consistent with each other, which suggests that they belong to an isospin triplet.
Categories: hep-ex