Study of the $D^0\to K^-\mu^+\nu_\mu$ dynamics and test of lepton flavor universality with $D^0\to K^-\ell^+\nu_\ell$ decays

TL;DR

This study precisely measures the decay rate of D0 to K mu nu and tests lepton flavor universality, finding results consistent with the Standard Model and providing improved determinations of key parameters like form factors and CKM matrix elements.

Contribution

The paper provides the most precise measurement of the D0 to K mu nu branching fraction and tests lepton flavor universality with no observed violation, also extracting form factors and CKM parameters.

Findings

Branching fraction of D0 to K mu nu measured as 3.413% with improved precision.

The ratio of muon to electron decay modes is 0.974, consistent with lepton flavor universality.

Determined form factor f_+^K(0) and CKM element |V_cs| with reduced uncertainties.

Abstract

Using $e^+e^-$ annihilation data of $2.93~\mathrm{fb}^{-1}$ collected at center-of-mass energy $\sqrt{s}=3.773$ GeV with the BESIII detector, we measure the absolute branching fraction of $D^{0}\to K^{-}\mu^{+}\nu_{\mu}$ with significantly improved precision: ${\mathcal B}_{D^{0}\to K^{-}\mu^{+}\nu_{\mu}}=(3.413\pm0.019_{\rm stat.}\pm0.035_{\rm syst.})\%$. Combining with our previous measurement of ${\mathcal B}_{D^0\to K^-e^+\nu_e}$, the ratio of the two branching fractions is determined to be ${\mathcal B}_{D^0\to K^-\mu^+\nu_\mu}/{\mathcal B}_{D^0\to K^-e^+\nu_e}=0.974\pm0.007_{\rm stat.}\pm0.012_{\rm syst.}$, which agrees with the theoretical expectation of lepton flavor universality within the uncertainty. A study of the ratio of the two branching fractions in different four-momentum transfer regions is also performed, and no evidence for lepton flavor universality violation is found with current statistics. Taking inputs from global fit in the standard model and lattice quantum chromodynamics separately, we determine $f_{+}^{K}(0)=0.7327\pm0.0039_{\rm stat.}\pm0.0030_{\rm syst.}$ and $|V_{cs}| = 0.955\pm0.005_{\rm stat.}\pm0.004_{\rm syst.}\pm0.024_{\rm LQCD}$.