Precision Measurement of B(D+ -> mu+ nu) and the Pseudoscalar Decay Constant fD+

TL;DR

This paper reports a precise measurement of the D+ meson leptonic decay rate, leading to an accurate determination of the decay constant fD+ and testing CP violation symmetry.

Contribution

It provides the most precise measurement to date of B(D+ -> mu+ nu) and derives a new value for fD+, improving constraints on theoretical models.

Findings

Measured B(D+ -> mu+ nu) with high precision

Derived fD+ value consistent with theoretical predictions

Set upper limits on B(D+ -> tau+ nu) and B(D+ -> e+ nu)

Abstract

We measure the branching ratio of the purely leptonic decay of the D+ meson with unprecedented precision as B(D+ -> mu+ nu) = (3.82 +/- 0.32 +/- 0.09)x10^(-4), using 818/pb of data taken on the psi(3770) resonance with the CLEO-c detector at the CESR collider. We use this determination to derive a value for the pseudoscalar decay constant fD+, combining with measurements of the D+ lifetime and assuming |Vcd| = |Vus|. We find fD+ = (205.8 +/- 8.5 +/- 2.5) MeV. The decay rate asymmetry [B(D+ -> mu+ nu)-B(D- -> mu- nu)]/[B(D+ -> mu+ nu)+B(D- -> mu- nu)] = 0.08 +/- 0.08, consistent with no CP violation. We also set 90% confidence level upper limits on B(D+ -> tau+ nu) < 1.2x10^(-3) and B(D+ -> e+ nu) < 8.8x10^(-6).