New a1(1420) state: Structure, mass, and width

The structure, spectroscopic parameters and width of the resonance with quantum numbers J(PC) = 1(++) discovered by the COMPASS Collaboration and classified as the a(1)(1420) meson are examined in the context of QCD sum rule method. In the calculations the axial-vector meson a(1)(1420) is treated as a fourquark state with the diquark-antidiquark structure. The mass and current coupling of a(1)(1420) are evaluated using QCD two-point sum rule approach. Its observed decay mode a(1)(1420) -> f (0)(980)pi, and kinematically allowed ones, namely a(1) -> K*(+/-) K--/+, a(1) -> K*(0)(K) over bar (0) and a(1) -> (K) over bar*K-0(0) channels are studied employing QCD sum rules on the light-cone. Our prediction for the mass of the a(1)(1420) state m(a1) = 1416(-79)(+81) MeV is in excellent agreement with the experimental result. Width of this state Gamma = 145.52 +/- 20.79 MeV within theoretical and experimental errors is also in accord with the COMPASS data.