Observation of the Resonant Character of theZ(4430)−State

Abstract

Resonant structures in B^{0}→ψ^{'}π^{-}K^{+} decays are analyzed by performing a four-dimensional fit of the decay amplitude, using pp collision data corresponding to 3 fb^{-1} collected with the LHCb detector. The data cannot be described with K^{+}π^{-} resonances alone, which is confirmed with a model-independent approach. A highly significant Z(4430)^{-}→ψ^{'}π^{-} component is required, thus confirming the existence of this state. The observed evolution of the Z(4430)^{-} amplitude with the ψ^{'}π^{-} 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^{+}.

The hidden-charm pentaquark and tetraquark states

“…[108], LHCb not only confirmed the existence of the Z + (4430), but also found a new structure the Z + (4240) in the π − ψ(3686) invariant mass distribution of B 0 → K + π − ψ(3686) decay with a statistical significance of 6σ, as shown in Fig. 16.…”

“…Besides these Belle experiments, the LHCb Collaboration also confirmed the existence of the Z + (4430), by performing a four-dimensional fit in the analysis of the π − ψ(3686) invariant mass distribution in the B 0 → K + π − ψ(3686) decay [108], as shown in Fig. 13.…”

“…LHCb LHCb LHCb Figure 13: (Color online) The four-dimensional fit to study the B 0 → K + π − ψ(3686) decays, performed by LHCb [108]. The red solid and brown dashed histograms represent the total amplitude with and without the Z + (4430), respectively.…”

Dalitz plot analysis ofB0→D¯0π+π−decays

“…The value for the radius of the resonance, r BW , is taken to be 1.6 GeV −1 × ℏc (¼ 0.3 fm) [78]. The function T L ðxÞ represents the angular distribution for the decay of a spin L resonance.…”

Results from b-physics

“…The LHCb Collaboration performed an amplitude fit to a large sample of B 0 → ψ ′ K + π − decays and provided the first independent confirmation of the existence of the Z(4430) resonance. Its spin-parity was determined to be 1 + [7]. The Argand diagram obtained for the Z(4430) amplitude is consistent with the resonant behavior.…”