# Measurement of the Decay Constant $f_D{_S^+}$ using $D_S^+ --> ell^+ nu

## TL;DR

This paper reports a measurement of the decay constant fDs using the Ds -> l+ nu channel, providing an experimental value and ratio with previous data, and comparing results with theoretical predictions.

## Contribution

The study presents a new measurement of the decay constant fDs and its ratio to fD+, combining different decay channels and previous data.

## Key findings

- Measured fDs = 274 ± 13 ± 7 MeV.
- Calculated ratio fDs/fD+ = 1.23 ± 0.11 ± 0.04.
- Results are compared with theoretical estimates.

## Abstract

We measure the decay constant fDs using the Ds -> l+ nu channel, where the l+ designates either a mu+ or a tau+, when the tau+ -> pi+ nu. Using both measurements we find fDs = 274 +-13 +- 7 MeV. Combining with our previous determination of fD+, we compute the ratio fDs/fD+ = 1.23 +- 0.11 +- 0.04. We compare with theoretical estimates.