Searches for New Physics at Belle II Experiment

Measurement of the branching fraction R(D*) ≡ Br(anti-B0 → D*+ τ- anti-ντ ) over Br(anti-B0 → D*+ ℓ− anti-νℓ), where the lepton ℓ− denotes an electron or a muon. The tau lepton is reconstructed in the decay of purely leptonic τ− → e− anti- νe ντ and τ− → μ− anti-νμ ντ. In the Standard Model, the semileptonic decays of anti-B0 → D*+ ℓ− anti-νℓ proceed via first-order electroweak interaction and are mediated by W boson. The W boson couples equally to the three lepton generations: e, μ, and τ as known as the Lepton Flavor Universality symmetry. Decays involving the high mass τ lepton in the semitauonic decays of anti- B0 → D*+ τ− anti-ντ provide a sensitive probe to additional amplitudes such as those involving an intermediate Higgs boson or a leptoquark being mediated in the b → c τ ν transition. The precise measurement of these ratios, R(D*), is sensitive to new physics contributions in the form of a charged Higgs boson.