Properties of the ηq leading-twist distribution amplitude and its effects to the B/D+→η(′)ℓ+νℓ decays.

The η (′) -mesons in the quark-flavor basis are mixtures of two mesonic states | η q ⟩ = | u ¯ u + d ¯ d ⟩ / 2 and | η s ⟩ = | s ¯ s ⟩. In previous work, we have made a detailed study on the η s leading-twist distribution amplitude by using the D s + meson semileptonic decays. As a sequential work, in the present paper, we fix the η q leading-twist distribution amplitude by using the light-cone harmonic oscillator model for its wave function and by using the QCD sum rules within the QCD background field to calculate its moments. The input parameters of η q leading-twist distribution amplitude ϕ 2 ; η q at the initial scale μ 0 ∼ 1 GeV are fixed by using those moments. The QCD sum rules for the 0 th -order moment can also be used to fix the magnitude of η q decay constant, giving f η q = 0.141 ± 0.005 GeV. As an application of ϕ 2 ; η q , we calculate the transition form factors B (D) + → η (′) by using the QCD light-cone sum rules up to twist-4 accuracy and by including the next-to-leading order QCD corrections to the leading-twist part, and then fix the related CKM matrix element and the decay width for the semi-leptonic decays B (D) + → η (′) ℓ + ν ℓ. [ABSTRACT FROM AUTHOR]