Abstract
We revisit QCD calculations of radiative heavy meson decay form factors by including the subleading power corrections from the twist-two photon distribution amplitude at next-to-leading-order in αs with the method of the light-cone sum rules (LCSR). The desired hard-collinear factorization formula for the vacuum-to-photon correlation function with the interpolating currents for two heavy mesons is constructed with the operator- product-expansion technique in the presence of evanescent operators. Applying the back- ground field approach, the higher twist corrections from both the two-particle and three- particle photon distribution amplitudes are further computed in the LCSR framework at leading-order in QCD, up to the twist-four accuracy. Combining the leading power “point- like” photon contribution at tree level and the subleading power resolved photon corrections from the newly derived LCSR, we update theory predictions for the nonperturbative couplings describing the electromagnetic decay processes of the heavy mesons H∗±→ H±γ, H∗0→ H0γ, {H_s^{ast}}^{pm } → {H}_s^{pm } γ (with H = D, B). Furthermore, we perform an exploratory comparisons of our sum rule computations of the heavy-meson magnetic couplings with the previous determinations based upon different QCD approaches and phenomenological models.
Highlights
Employing the method of the two-point QCD sum rules (QCDSR), the electromagnetic D∗(p + q) → D(q) γ(p) decay form factors were estimated at leading-order (LO) in αs [14] by taking into account the subleading power corrections at the dimension-5 quark-gluon condensate accuracy
In an attempt to eliminate the substantial contamination from the non-diagonal transitions of constructing the traditional QCDSR for hadronic matrix elements at small momentum transfer, the technically improved sum rules based upon the light-cone operator-product-expansion (OPE) for the corresponding QCD correlation functions have been constructed [21] for computing the radiative heavy meson decay form factors with the subleading power corrections from the photon light-cone distribution amplitudes (LCDA) at the-twist-four accuracy
The resummation improved hard-collinear factorization formula for the vacuumto-photon correlation function defined with the two interpolating currents for the vector and pseudoscalar heavy mesons was established by applying the evanescent operator approach and the two-loop RG equation of the twist-two photon distribution amplitude
Summary
The purpose of this section is to present the tree-level LCSR for the “point-like” photon contribution to the M ∗M γ coupling including the SU(3)-flavour symmetry breaking effect due to the light-quark mass correction. Since the SU(3)-flavour symmetry breaking effect for the obtained light-cone matrix element γ(p, η∗)|q(z) γμ⊥ γ5 q(0)|0 from the infrared subtraction program (see [47, 48] for discussions in the context of the vector meson distribution amplitudes) has not been investigated systematically at present, we will not take into account the light quark mass correction to the perturbative contribution shown in figure 1(b) further, which is apparently suppressed by one power of ΛQCD/mQ in the heavy quark expansion. Matching the perturbative QCD factorization formula (2.19) of the “point-like” photon contribution with the corresponding hadronic representation (2.22) and performing the double Borel transformation with respect to the variables (p + q)2 → M12 and q2 → M22, we derive the sum rules for the coupling constant gM∗Mγ of our interest including the light quark mass correction fP fV μP mV gM(pe∗rM) γ exp −. It remains interesting to investigate whether the higherorder QCD corrections to the “point-like” photon contributions (see [51] for discussions in the context of J/ψ → ηc γ) could alleviate such numerical cancellation
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