Observation of a charged charmonium-like state Z_C(3900)

Using data samples collected with the BESIII detector at an e⁺e^- centre-of-mass energy of 4.26 GeV and with the Belle detector on or near the (nS), n=1, …, 5, resonances, the e⁺e^--→ p⁺p^-J/y process was investigated through different approaches. Both detectors observed a charged charmonium-like state in the invariant mass distribution of p^±J/y . This new structure, called Z^C(3900),couples strongly to a charmonium and is charged, so it cannot be a conventional charmonium state, but can be interpreted as an exotic hadron with at least four quarks.