By analyzing 2.93 fb-1 of data collected at √s = 3.773 GeV with the BESIII detector, we measure the absolute branching fraction B(D+ → K 0µ+νµ) = (8.72 ±0.07stat. ±0.18sys.) %, which is consistent with previous measurements within uncertainties but with significantly improved precision. Combining the Particle Data Group values of B(D0 → K-µ+νµ), B(D+ → K 0e+νe), and the lifetimes of the D0 and D+ mesons with the value of B(D+ → K 0µ+νµ) measured in this work, we determine the following ratios of partial widths: Γ(D0 → K-µ+νµ)/Γ(D+ → K 0µ+νµ) = 0.963 ± 0.044 and Γ(D+ → K 0µ+νµ)/Γ(D+ → K 0e+νe) = 0.988±0.033. mechanisms with better accuracy. In addition, the improved B(D+ → K 0µ+νµ) can also be used to precisely determine the form factor f K+ (0) and the quark mixing matrix element |Vcs| from D semileptonic decays . Previous measurements of B(D+ → K 0µ+νµ) come from MARKIII , FOCUS  and BESII . In this paper, by analyzing 2.93 fb-1 of data [7,8] collected at the centerof- mass energy of √s = 3.773 GeV by the BESIII detector , we determine the absolute branching fraction of D+ → K 0µ+νµ. Throughout the paper, charge conjugation is implied.
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