Lepton-Flavor-Dependent Angular Analysis of B→K^{*}ℓ^{+}ℓ^{-}

Area of Science:

• High-energy particle physics
• Experimental particle physics

Background:

• The Standard Model (SM) of particle physics successfully describes fundamental particles and forces.
• Lepton flavor universality (LFU) is a key principle of the SM, stating that leptons of different flavors (electron, muon, tau) interact similarly.
• Deviations from LFU in B meson decays could indicate new physics beyond the SM.

Purpose of the Study:

• To measure angular observables in the B→K^{*}ℓ^{+}ℓ^{-} decay.
• To test lepton flavor universality by comparing the decay rates and distributions for electrons and muons.
• To search for potential signs of new physics beyond the Standard Model.

Main Methods:

• Analysis of a large dataset of 772×10^{6} BB[over ¯] pairs collected by the Belle detector at the KEKB collider.
• Measurement of angular distributions of the decay products in B→K^{*}ℓ^{+}ℓ^{-} decays.
• Comparison of branching ratios and angular observables between electron and muon decay modes.

Main Results:

• Measurements of angular observables in the B→K^{*}ℓ^{+}ℓ^{-} decay are presented.
• The test of lepton flavor universality shows consistency with SM expectations.
• A local discrepancy of 2.6σ from SM predictions is observed in the muon decay modes.

Conclusions:

• The study provides precise measurements of B→K^{*}ℓ^{+}ℓ^{-} decay observables.
• Current data are consistent with lepton flavor universality, though a mild tension persists in muon channels.
• Further data collection and analysis are needed to clarify the observed discrepancy and its implications for new physics.