A state with minimal quark content ccu~d~ has been observed in the full dataset collected by the LHCb experiment in Run1&2. This is the first observation of a new class of exotic hadrons, containing two same-sign heavy quarks. This exotic state manifests itself as a narrow peak in the mass spectrum of D0D0π+ mesons just below the D∗+D0 mass threshold. Study of the DD and Dpi mass distributions suggest the interpretation of the state as an isoscalar ground Tcc+ tetraquark with spin-parity numbers JP=1+. Fundamental resonance parameters including the pole position, scattering length, effective range and compositeness are measured to reveal important information about the nature of this new state. In addition, an unexpected dependence of the production rate as a function of track multiplicity is observed.
Michelangelo Mangano, Monica Pepe-Altarelli and Pedro Silva.