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 four-quark 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 $a_1(1420)\to f_0(980)\pi$, and kinematically allowed ones, namely $a_1\to K^{*\pm }{K}^{\mp }$, $a_1\to K^{*0}{\overline{K}}^0$ and $a_1\to {\overline{K}}^{*0}{K}^0$ channels are studied employing QCD sum rules on the light-cone. Our prediction for the mass of the $a_1(1420)$ state $m_{a_1}={1416}_{-79}^{+81}\mathrm{MeV}$ is in excellent agreement with the experimental result. Width of this state $\mathrm{\Gamma }=145.52\pm 20.79\mathrm{MeV}$ within theoretical and experimental errors is also in accord with the COMPASS data.

• Received 16 November 2017

DOI:https://doi.org/10.1103/PhysRevD.97.054001

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Published by the American Physical Society