Measurements of the absolute branching fractions for D->Kbar pi e+ nu_e, D-> K*bar e+nu_e and determination of Gamma(D+ -> K*0bar e+ nu_e)/Gamma(D+ -> K0bar e+nu_e)

Using the data of about 33 pb$^{-1}$ collected at and around 3.773 GeV with the BES-II detector at the BEPC collider, we have studied the exclusive semileptonic decays $D^+ \to K^-π^+ e^+ν_e$, $D^0 \to \bar K^0π^-e^+ν_e$, $D^+ \to \bar K^{*0}e^+ν_e$ and $D^0 \to K^{*-}e^+ν_e$. The absolute branching fractions for the decays are measured to be ${BF}(D^+ \to K^-π^+e^+ν_e)=(3.50\pm0.75\pm0.27)$, ${BF}(D^0 \to \bar K^0π^-e^+ν_e)=(2.61\pm1.04\pm0.28)$, ${BF}(D^+ \to \bar K^{*0}e^+ν_e)=(5.06\pm1.21\pm0.40)$ and ${BF}(D^0 \to K^{*-}e^+ν_e)=(2.87\pm 1.48\pm 0.39)$. The ratio of the vector to pseudoscalar semileptonic decay rates $Γ(D^+\to\bar K^{*0}e^+ν_e)/Γ(D^+\to\bar K^0e^+ν_e)$ is determined to be $0.57\pm0.17\pm0.02$.

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