Observation of the resonant character of the Z (4430)^- state

Resonant structures in B0 -K+ decays are analyzed by performing a four-dimensional fit of the decay amplitude, using pp collision data corresponding to 3fb-1 collected with the LHCb detector. The data cannot be described with K+Ï€- resonances alone, which is confirmed with a model-independent approach. A highly significant Z(4430)- φπ- component is required, thus confirming the existence of this state. The observed evolution of the Z(4430)- amplitude with the Ïâ€Ï€- mass establishes the resonant nature of this particle. The mass and width measurements are substantially improved. The spin parity is determined unambiguously to be 1+.