B→πll Form Factors for New Physics Searches from Lattice QCD.

Area of Science:

• High Energy Physics
• Quantum Chromodynamics (QCD)
• Particle Physics

Background:

• The rare B→πℓ^{+}ℓ^{-} decay is a key process for probing flavor-changing neutral currents.
• This decay is sensitive to potential new physics beyond the Standard Model.
• Previous studies lacked a complete set of form factors for precise theoretical predictions.

Purpose of the Study:

• To perform the first ab initio QCD calculation of the B→π tensor form factor, f_{T}.
• To provide a complete set of hadronic form factors (f_{T}, f_{+}, f_{0}) for B→π semileptonic decays.
• To obtain the most precise theoretical prediction for the B→πℓ^{+}ℓ^{-} decay branching ratio within the Standard Model.

Main Methods:

• Utilized ab initio Quantum Chromodynamics (QCD) calculations to determine the B→π tensor form factor.
• Combined the calculated tensor form factor with previously computed vector and scalar form factors.
• Parametrized the hadronic contributions to B→π semileptonic decays for Standard Model extensions.

Main Results:

• Successfully computed the B→π tensor form factor f_{T} from first principles.
• Calculated the total branching ratio for B^{+}→π^{+}μ^{+}μ^{-} within the Standard Model as 20.4(2.1)×10^{-9}.
• Achieved the most precise theoretical determination of this branching ratio to date.

Conclusions:

• The theoretical branching ratio for B^{+}→π^{+}μ^{+}μ^{-} is in excellent agreement with recent LHCb experimental measurements.
• The calculated form factors provide crucial inputs for testing the Standard Model and searching for new physics.
• This work establishes a robust theoretical framework for analyzing rare B meson decays.