Observation of the Leptonic Decay D^{+}→τ^{+}ν_{τ}

Area of Science:

• Particle Physics
• High Energy Physics
• Quantum Chromodynamics

Background:

• The Standard Model of particle physics predicts lepton flavor universality.
• Previous experimental efforts have not yet observed the decay of D+ mesons into tau neutrinos.
• Understanding D+ meson decays is crucial for testing fundamental symmetries in nature.

Purpose of the Study:

• To report the first observation of the D+→τ+ντ decay.
• To measure the branching fraction of D+→τ+ντ and the ratio Rτ/μ.
• To test lepton flavor universality in D+ meson decays.

Main Methods:

• Analysis of experimental data from particle collisions.
• Statistical analysis to determine the significance of the observed signal.
• Comparison of measured branching fractions with theoretical predictions.

Main Results:

• The first observation of D+→τ+ντ decay with a significance of 5.1σ.
• Measurement of B(D+→τ+ντ) = (1.20±0.24stat±0.12syst)×10−3.
• Determination of Rτ/μ = Γ(D+→τ+ντ)/Γ(D+→μ+νμ) = 3.21±0.64stat±0.43syst, consistent with the Standard Model.

Conclusions:

• The results provide the first direct evidence for D+→τ+ντ decay.
• The measured ratio Rτ/μ supports the principle of lepton flavor universality.
• The study contributes to precise measurements of fundamental parameters like the D+ decay constant and |Vcd|.