$a_1(1260), a_1(1420)$ and the production in heavy meson decays

Abstract

The $a_1(1420)$ with $I^G(J^{PC})= 1^-(1^{++})$ observed in the $π^+ f_0(980)$ final state in the $π^-p\to π^+π^-π^- p$ process by the COMPASS collaboration seems unlikely to be an ordinary $\bar qq$ mesonic state. Available theoretical explanations include tetraquark or rescattering effects due to $a_1(1260)$ decays. If the $a_1(1420)$ were induced by the rescattering, its production rates are completely determined by those of the $a_1(1260)$. In this work, we propose to explore the ratios of branching fractions of heavy meson weak decays into the $a_1(1420)$ and $a_1(1260)$, and testing the universality of these ratios would be a straightforward way to validate/invalidate the rescattering explanation. The decay modes include in the charm sector the $D^0\to a_1^-\ell^+ν$ and $D^0\to π^\pm a_1^\mp$, and in the bottom sector $\overline B^0\to a_1^+ \ell^- \barν$, $B\to D a_1, π^\pm a_1^\mp$, $B_c\to J/ψa_1$ and $Λ_b\to Λ_c a_1$. We calculate the branching ratios for various decay modes into the $a_1(1260)$. The numerical results indicate that there is a promising prospect to study these decays on experiments including BES-III, LHCb, Babar, Belle and CLEO-c, the forthcoming Super-KEKB factory and the under-design Circular Electron-Positron Collider. Experimental analyses in future will lead to a deeper understanding of the nature of the $a_1(1420)$.