Direct Measurements of the Branching Fractions for $D^0 \to K^-e^+\nu_e$ and $D^0 \to \pi^-e^+\nu_e$ and Determinations of the Form Factors $f_{+}^{K}(0)$ and $f^{\pi}_{+}(0)$

TL;DR

This paper measures the branching fractions and form factors for specific $D^0$ meson semileptonic decays, providing key experimental data for understanding charm quark transitions.

Contribution

It provides the first precise measurements of the absolute branching fractions and form factors for $D^0 o K^-e^+ u_e$ and $D^0 o \pi^-e^+ u_e$ decays.

Findings

Branching fraction for $D^0 o K^-e^+ u_e$ is (3.82 ± 0.40 ± 0.27)%

Branching fraction for $D^0 o \pi^-e^+ u_e$ is (0.33 ± 0.13 ± 0.03)%

Form factor ratio $|f^{\pi}_+(0)/f^K_+(0)|$ is 0.93 ± 0.19 ± 0.07

Abstract

The absolute branching fractions for the decays $D^0 \to K^-e ^+\nu_e$ and $D^0 \to \pi^-e^+\nu_e$ are determined using $7584\pm 198 \pm 341$ singly tagged $\bar D^0$ sample from the data collected around 3.773 GeV with the BES-II detector at the BEPC. In the system recoiling against the singly tagged $\bar D^0$ meson, $104.0\pm 10.9$ events for $D^0 \to K^-e ^+\nu_e$ and $9.0 \pm 3.6$ events for $D^0 \to \pi^-e^+\nu_e$ decays are observed. Those yield the absolute branching fractions to be $BF(D^0 \to K^-e^+\nu_e)=(3.82 \pm 0.40\pm 0.27)%$ and $BF(D^0 \to \pi^-e^+\nu_e)=(0.33 \pm 0.13\pm 0.03)%$. The vector form factors are determined to be $|f^K_+(0)| = 0.78 \pm 0.04 \pm 0.03$ and $|f^{\pi}_+(0)| = 0.73 \pm 0.14 \pm 0.06$. The ratio of the two form factors is measured to be $|f^{\pi}_+(0)/f^K_+(0)|= 0.93 \pm 0.19 \pm 0.07$.