Direct Measurement of the Pseudoscalar Decay Constant fD+

TL;DR

This paper reports a direct measurement of the branching fraction for the decay D+ to mu+ nu and determines the pseudoscalar decay constant fD+ using data from BES-II at BEPC, providing key insights into charm meson decay properties.

Contribution

It presents the first direct measurement of the D+ meson decay constant fD+ from experimental data, improving understanding of charm quark dynamics.

Findings

Branching fraction BF(D+ to mu+ nu) = (0.122^{+0.111}_{-0.053} ext{(stat)} ext{+} 0.010 ext{(sys)})%

Pseudoscalar decay constant fD+ = (371^{+129}_{-119} ext{(stat)} ext{+} 25 ext{(sys)}) MeV

Observation of leptonic decay events consistent with theoretical expectations.

Abstract

The absolute branching fraction of $D^+ \to \mu^+ \nu$ has been directly measured by an analysis of a data sample of about 33 ${\rm pb^{-1}}$ collected around $\sqrt{s}=3.773$ GeV with the BES-II at the BEPC. At these energies, $D^-$ meson is produced in pair as $e^+e^-\to D^{+} D^{-}$. A total of $5321 \pm 149 \pm 160$ $D^-$ mesons are reconstructed from this data set. In the recoil side of the tagged $D^-$ mesons, $2.67\pm1.74$ purely leptonic decay events of $D^+ \to \mu^+ \nu$ are observed. This yields a branching fraction of $BF(D^+ \to \mu^+ \nu_{\mu}) = (0.122^{+0.111}_{-0.053}\pm 0.010)%$, and a corresponding pseudoscalar decay constant $f_{D^+}=(371^{+129}_{-119}\pm 25)$ MeV.