A dispersive estimate of the a0(980) contribution to hadronic light-by-light scattering in (𝑔 − 2)µ

Abstract

A dispersive implementation of the a0(980) resonance to (𝑔 − 2)µ requires the knowledge of the double-virtual S-wave γ * γ * → πη / KK¯I = 1 am plitudes. To obtain these amplitudes we used a modified coupled-channel Muskhelishvili-Omnès formalism, with the input from the left-hand cuts and the hadronic Omnès function. The latter were obtained using a data-driven N/D method in which the fits were performed to the different sets of experimental data on two-photon fusion processes with πη and KK¯ final states. This yields the preliminary dispersive estimate aμHLbL[a0(980)]resc. = -0.46(2) × 10-11.