Review and Report on Results of Leptonic Decays of $D^+$ and $D^+_s$ Mesons

TL;DR

This paper reviews experimental results on leptonic decays of $D^+$ and $D_s^+$ mesons, highlighting precise measurements of decay constants and CKM matrix elements that test QCD predictions and probe for new physics beyond the Standard Model.

Contribution

It provides a comprehensive summary of over 25 years of experimental data on leptonic $D$ meson decays, including new unpublished results and their implications for theory and new physics.

Findings

Decay constants measured with 1.6-2.4% accuracy

CKM matrix elements $|V_{cd}|$ and $|V_{cs}|$ determined from leptonic decays

Results used to test QCD calculations and search for new physics

Abstract

In the last 25 years, many $e^+e^-$ experiments and fixed-target experiments performed to search for and study the leptonic decays of the $D^+$ and $D^+_s$ mesons. By 2012, more than 530 signal events of the $D^+$ leptonic decays and about $4\times10^3$ signal events of the $D^+_s$ leptonic decays have been accumulated at these experiments. With these leptonic decay signal events, both decay constants $f_{D^+}$ and $f_{D_s^+}$ are, respectively, measured at an accuracy level of 2.4% and 1.6%, which can be used to more precisely test the LQCD calculations of the decay constants. Comparing these precisely measured $f_{D^+}$ and $f_{D_s^+}$ with those predicted with theories based on QCD provides some information about New Physics beyond the Standard Model. In addition to these, with the measured branching fractions for $D^+\rightarrow l^+\nu$ and $D_s^+\rightarrow l^+\nu$ decays, the CKM matrix elements $|V_{\rm cd}|$ and $|V_{\rm cs}|$ can be determined. Comparing these $|V_{\rm cd}|$ and $|V_{\rm cs}|$ to those determined from the CKMfitter or extracted from $D$ meson semileptonic decays can also provide some information about the New Physics. In this article, we review and report the results on the leptonic decays of $D^+$ and $D^+_s$ mesons measured at different experiments. For the results which have already been published, we review these in shorter summaries, while for the results which have not been published or have not been reported yet before we report these with more detailed discussion.