Improved measurements of $D^0 \to K^-\ell^+\nu_\ell$ and $D^+ \to \bar K^0\ell^+\nu_\ell$

TL;DR

This paper presents precise measurements of branching fractions for specific D meson semileptonic decays and extracts the hadronic form factor and CKM matrix element using BESIII data, improving understanding of charm quark transitions.

Contribution

The study provides the most precise measurements to date of D meson semileptonic decay branching fractions and determines the product of the form factor and CKM element, refining parameters critical for testing the Standard Model.

Findings

Branching fractions for D0 and D+ semileptonic decays measured with high precision.

Determination of the product f_+^K(0)|V_cs| with improved accuracy.

Extraction of f_+^K(0) and |V_cs| values consistent with theoretical predictions.

Abstract

Using 7.93 fb$^{-1}$ of $e^+e^-$ collision data collected at the center-of-mass energy of 3.773 GeV with the BESIII detector, we measure the absolute branching fractions of $D^0\to K^-e^+\nu_e$, $D^0\to K^-\mu^+\nu_\mu$, $D^+\to \bar K^0e^+\nu_e$, and $D^+\to \bar K^0\mu^+\nu_\mu$ to be $(3.521\pm0.009_{\rm stat.}\pm0.016_{\rm syst.}) \%$, $(3.419\pm0.011_{\rm stat.}\pm0.016_{\rm syst.}) \%$, $(8.864\pm0.039_{\rm stat.}\pm0.082_{\rm syst.}) \%$, and $(8.665\pm0.046_{\rm stat.}\pm0.084_{\rm syst.}) \%$, respectively. By performing a simultaneous fit to the partial decay rates of these four decays, the product of the hadronic form factor $f^K_+(0)$ and the modulus of the $c\to s$ CKM matrix element $|V_{cs}|$ is determined to be $f^K_+(0)|V_{cs}|=0.7171\pm0.0011_{\rm stat.}\pm0.0013_{\rm syst.}$. Taking the value of $|V_{cs}|=0.97349\pm0.00016$ from the standard model global fit or that of $f^K_+(0)=0.7452\pm0.0031$ from the LQCD calculation as input, we derive the results $f^K_+(0)=0.7366\pm0.0011_{\rm stat.}\pm0.0013_{\rm syst.}$ and $|V_{cs}|=0.9623\pm0.0015_{\rm stat.}\pm0.0017_{\rm syst.}\pm0.0040_{\rm LQCD}$.