The new $a_1(1420)$ state: structure, mass and width

Abstract

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 $a_1\to K^{\ast \pm }{K}^{\mp }$, $a_1\to K^{\ast 0}{\bar{K}}^0$ and $a_1\to {\bar{K}}^{\ast 0}{K}^0$ 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 $\Gamma =145.52\pm 20.79\mathrm{MeV}$ within theoretical and experimental errors is also in accord with the COMPASS data.

11 Pages and 3 Figures, To be published in Phys. Rev. D

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• Role of the triangle mechanism in the ${\Lambda }_b\to {\Lambda }_c{\pi }^{-}{f}_0(980)$ reaction
• Probing an axial-vector tetraquark $Z_s$ via its semileptonic decay $Z_s\to X(4274)\overline{l}{\nu }_l$
• Spectroscopy of $a_1$ mesons from lattice QCD with the truncated overlap fermions
• Rare Radiative Decays of Vector and Axial-Vector $B_c$ Mesons to $(D_s,D_s^{\ast },D_{s1})$ Final States
• The scalar and pseudoscalar hidden-charm tetraquark states with QCD sum rules