Measurement of the Branching Fraction Ratios R(D^{+}) and R(D^{*+}) Using Muonic τ Decays

Area of Science:

• High Energy Physics
• Particle Physics
• Hadron Spectroscopy

Background:

• The Standard Model (SM) of particle physics predicts specific ratios for B meson decays.
• Deviations from SM predictions could indicate new physics beyond the Standard Model.
• Previous measurements of B meson decays involving tau leptons have shown some tension with SM predictions.

Purpose of the Study:

• To precisely measure the branching fraction ratios R(D+) and R(D*+) for B0 decays.
• To compare these ratios with their muonic counterparts.
• To test the predictions of the Standard Model in B meson decays involving heavy quarks and leptons.

Main Methods:

• Utilized a data sample of 2.0 fb^-1 from proton-proton collisions at 13 TeV collected by the LHCb experiment.
• Reconstructed final states by combining D+ mesons with tau- -> mu- nu_tau candidates.
• Reconstructed the D+ meson via the D+ -> K- pi+ pi+ decay channel.

Main Results:

• Measured R(D+) = 0.249 ± 0.043 (stat) ± 0.047 (syst).
• Measured R(D*+) = 0.402 ± 0.081 (stat) ± 0.085 (syst).
• The measurements show compatibility with the Standard Model predictions, with a correlation coefficient of -0.39.

Conclusions:

• The measured branching fraction ratios are consistent with the Standard Model.
• This study contributes precise measurements to the field of B meson decays.
• Further studies with larger datasets may refine these measurements and probe for potential new physics.