Hadronic Charmed Meson Decays Involving Axial Vector Mesons

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Cabibbo-allowed charmed meson decays into a pseudoscalar meson and an axial-vector meson are studied. The charm to axial-vector meson transition form factors are evaluated in the Isgur-Scora-Grinstein-Wise quark model. The dipole momentum dependence of the D→ K transition form factor and the presence of a sizable long-distance W-exchange are the two key ingredients for understanding the data of D→ Ka₁. The K₁ₐ-K₁B mixing angle of the strange axial-vector mesons is found to be ≈ ±37∘ or ±58∘ from τ→ K₁ντ decays. The study of D→ K₁(1270)π, K₁(1400)π decays excludes the positive mixing-angle solutions. It is pointed out that an observation of the decay D⁰→ K₁-(1400)π+ at the level of 5× 10⁻⁴ will rule out θ≈ -37∘ and favor the solution θ≈ -58∘. Though the decays D⁰→ K₁⁰π⁰ are color suppressed, they are comparable to and even larger than the color-allowed counterparts: K₁⁰(1270)π⁰ K₁-(1270)π+ and K₁⁰(1400)π⁰> K₁-(1400)π+. The finite width effect of the axial-vector resonance is examined. It becomes important for a₁(1260) in particular when its width is near 600 MeV.