Direct pion emission in D*~+→D~+π decays

The QCD multipole expansion(QCDME) is based on quantum field theory and has been extensively applied to study transitions among Υ and ψ family members. As it refers to non-perturbative QCD, however, it has only a certain application range. Even though it successfully explains the transition data among members of the Υ(ψ) family, as Eichten indicates, beyond the production threshold of mediate states it fails to match data by several orders of magnitude. In this work, by studying a simple decay mode D*→D +π~0, where a pion may be emitted before D* transitions into D, we analyze the contribution of QCD multipole expansion. As the Dπ portal is open,the dominant contribution is an OZI-allowed process where a light quark-pair is excited out from vacuum, and its contribution can be evaluated by the ~3P_0 model. Since direct pion emission is OZI-suppressed and violates isospin conservation, its contribution must be much smaller than the dominant one. By a careful calculation, we estimate that the QCDME contribution should be 3–4 orders smaller than the dominant contribution and this result can offer a quantitative interpretation for Eichten's statement.

Direct pion emission in D*+→D+π decays

The QCD multipole expansion (QCDME) is based on quantum field theory and has been extensively applied to study transitions among Υ and ψ family members. As it refers to non-perturbative QCD, however, it has only a certain application range. Even though it successfully explains the transition data among members of the Υ (ψ) family, as Eichten indicates, beyond the production threshold of mediate states it fails to match data by several orders of magnitude. In this work, by studying a simple decay mode D^*→D+π⁰, where a pion may be emitted before D^* transitions into D, we analyze the contribution of QCD multipole expansion. As the Dπ portal is open, the dominant contribution is an OZI-allowed process where a light quark-pair is excited out from vacuum, and its contribution can be evaluated by the ³P₀ model. Since direct pion emission is OZI-suppressed and violates isospin conservation, its contribution must be much smaller than the dominant one. By a careful calculation, we estimate that the QCDME contribution should be 3-4 orders smaller than the dominant contribution and this result can offer a quantitative interpretation for Eichten's statement.