b1 resonance in coupled πω, πφ scattering from lattice QCD

We present the fast lattice QCD calculation of coupled pi omega and pi phi scattering, incorporating coupled S and D-wave pi omega in J(P) = 1(+). Finite-volume spectra in three volumes arc determined via a variational analysis of matrices of two-point correlation functions, computed using large bases of operators resembling single-meson, two-meson, and three-meson structures, with the light-quark mass corresponding to a pion mass of m(pi) approximate to 391 MeV. Utilizing the relationship between the discrete spectrum of finite-volume energies and infinite-volume scattering amplitudes, we find a narrow axial-vector resonance (J(PC) = 1(+-)), the analogue of the b(1) meson, with mass m(R) approximate to 1380 MeV and width Gamma(R) approximate to 91 MeV. The resonance is found to couple dominantly to S-wave pi omega, with a much-suppressed coupling to D-wave pi omega, and a negligible coupling to pi phi consistent with the Okubo-Zweig-lizuka rule. No resonant behavior is observed in pi phi, indicating the absence of a putative low-mass Z(s) analogue of the Z(c) seen in pi J/psi. In order to minimally present the contents of a unitary three-channel scattering matrix, we introduce an n-channel generalization of the traditional two-channel Stapp parametrization.