An Investigation of D+--> tau+ nu

TL;DR

This paper investigates whether tau and mu leptons have identical couplings by measuring the decay rate ratio of D+ mesons to tau+ nu and mu+ nu, finding results consistent with lepton universality.

Contribution

First upper limit on the ratio of D+ decays to tau+ nu versus mu+ nu, testing lepton universality with experimental data.

Findings

The ratio R is less than 1.8 at 90% confidence level.

Measured branching fraction B(D+ -> tau+ nu) < 2.1 x 10^(-3).

Results are consistent with Standard Model predictions.

Abstract

We test whether or not the tau lepton manifests the same couplings as the mu lepton by investigating the relative decay rates in purely leptonic D+ meson decays. Specifically, we place the first upper limit on the ratio R=Gamma(D+ -> tau+ nu)/Gamma(D+ -> mu+ nu). We use 281 inverse pb of data accumulated at the psi(3770) resonance with the CLEO-c detector, to determine B(D+ -> tau+ nu) < 2.1 x 10^(-3) at 90% confidence level (C. L.). The ratio of R to the Standard Model expectation of 2.65 then is <1.8 at 90% C. L., consistent with the prediction of lepton universality.