An investigation of $D^{+} \to τ^{+} ν$

We test whether or not the

τ

lepton manifests the same couplings as the

μ

lepton by investigating the relative decay rates in purely leptonic

D^{+}

meson decays. We use

281 {pb}^{- 1}

of data accumulated at the

ψ (3770)

resonance with the CLEO-c detector, to limit

B (D^{+} \to τ^{+} ν) < 2.1 \times 10^{- 3}

at 90% confidence level (C.L.), thus allowing us to place the first upper limit on the ratio

R = Γ (D^{+} \to τ^{+} ν) / Γ (D^{+} \to μ^{+} ν)

. 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.

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An investigation ofD+→τ+ν