R(J/ψ) and B_{c}^{-}→J/ψℓ^{-}ν[over ¯]_{l} Lepton Flavor Universality Violating Observables from Lattice QCD.

Area of Science:

• High Energy Physics
• Quantum Chromodynamics
• Particle Physics

Background:

• The Bc meson is a key probe for studying fundamental particle interactions.
• Semileptonic decays of heavy mesons offer insights into the Standard Model and potential new physics.
• Lepton flavor universality is a cornerstone of the Standard Model, and deviations are actively sought.

Purpose of the Study:

• To compute the differential decay rate for the semitauonic decay channel of the Bc meson.
• To determine the ratio of branching fractions R(J/ψ) for Bc- → J/ψτ-ντ / Bc- → J/ψμ-νμ.
• To extend angular observables to Bc → J/ψℓν decays for probing new physics scenarios.

Main Methods:

• Utilizing lattice Quantum Chromodynamics (QCD) computations for B_c → J/ψ form factors.
• Calculating the differential decay rate for the semitauonic decay channel.
• Constructing the ratio of branching fractions R(J/ψ).

Main Results:

• The ratio of branching fractions was determined to be R(J/ψ) = 0.2582(38).
• A detailed error budget for the result was provided.
• Predictions for angular observables in Bc → J/ψℓν decays under various new physics scenarios were made.

Conclusions:

• The computed R(J/ψ) value provides a precise prediction within the Standard Model.
• The extended angular observables offer new tools to search for lepton flavor universality violating effects.
• These results contribute to the ongoing search for physics beyond the Standard Model.