The nature of light scalar mesons remains an unsolved puzzle in hadron physics, complicated by their large widths and controversial partonic structure. We propose to resolve this problem in a comprehensive study of isoscalar two-pion state (ππ ₒ), the signal channel of f₀ (980), through its light-cone distribution amplitudes (2πDAs). A key finding is that charge parity forces the twist-3 2πDAs to be asymmetric in the momentum fractions of the quark and antiquark. This property stands in stark contrast to the symmetric twist-3 distribution amplitudes of a conventional f₀ (980) meson, as derived from QCD sum rules in the narrow-width approximation. We calculate the Dₛ ππ ₒ transition form factors and discover a significant cancellation between the twist-2 and twist-3 contributions. This leads to a QCD prediction for the Dₛ^+ ππ ₒ e^+ νₑ decay width that is significantly smaller than the experimental measurement. Our results indicate that the lowest Fock state is not the dominant configuration of the isoscalar two-pion state produced in charm decays, in contrast to the case in B decays. Future precision measurements can constrain the high-twist 2πDAs associated with multi-particle Fock states, offering a new path to elucidate the structure of the light scalar mesons.
Cheng et al. (Fri,) studied this question.
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