Evidence for an excess of B→D*τ(-)ν(τ) decays

Area of Science:

• Particle Physics
• High Energy Physics
• Standard Model Physics

Background:

• The Standard Model (SM) of particle physics provides a successful framework for understanding fundamental particles and forces.
• Deviations from SM predictions in B meson decays can indicate the presence of new physics.
• The ratios R(D) and R(D*) probe lepton flavor universality in B meson decays.

Purpose of the Study:

• To report improved measurements of the ratios R(D) and R(D*).
• To test for new physics contributions, specifically those from a charged Higgs boson.
• To compare experimental results with Standard Model expectations.

Main Methods:

• Analysis of the full BABAR data sample.
• Measurement of branching fractions for B -> D(*) tau(-)nu and B -> D(*) l(-)nu (l=e, mu).
• Calculation of the ratios R(D) and R(D*).

Main Results:

• Measured R(D) = 0.440 ± 0.058 ± 0.042.
• Measured R(D*) = 0.332 ± 0.024 ± 0.018.
• Results exceed Standard Model predictions by 2.0σ for R(D) and 2.7σ for R(D*), with a combined 3.4σ disagreement.

Conclusions:

• The measured ratios R(D) and R(D*) show a significant deviation from Standard Model predictions.
• This deviation suggests the presence of new physics beyond the Standard Model.
• The observed excess cannot be explained by a charged Higgs boson within the type II two-Higgs-doublet model.