Study of electroweak penguin B decays at Belle II experiment

The electroweak b → sll (l = e, µ) transition is a flavor-changing neutral current process that mediates through a one-loop penguin diagram. The decay is considered to be a good probe for the New Physics as particles predicted in the beyond Standard Model theories can enter into the loop. The exclusive decay B → K (*) l + l − was first observed by the Belle experiment and it provides many observables such as the branching fraction, CP asymmetry, forward-backward asymmetry, and other angular observables. Recently, the LHCb experiment has reported some clue of a lepton flavor universality violation from the branching fraction ratio of the B → Kµ + µ − and B → Ke + e − decays. In this presentation, we report the status of the B → Kl + l − decay analysis at the Belle II experiment which started the data taking in 2019. We also, present an activity at the Belle II Chulalongkorn University group where we study the B → KJ/ψ decay which has the same topology as the B → Kl + l − .

RECENT RESULTS ON B DECAYS: Rare B Decay Highlights + Belle $b \to s\bar{q}q$ Time-dependent CPV

Highlights on recent experimental results on rare decays from asymmetric B-factories are reported. Also, the results on time-dependent CP violation measurements for decay modes where [Formula: see text] penguin diagram dominate from Belle are reported.

DIRECT CP VIOLATION AND NEW PHYSICS EFFECTS IN THE DECAY MODE B+→ϕK+

We study the direct CP violation effect in the decay mode B+→ϕK+. This decay mode is dominated by the loop induced [Formula: see text] penguin diagram with a tiny contribution from the annihilation diagram. Therefore, the standard model expectation of direct CP violation is negligibly small. Using QCD factorization approach we find the CP asymmetry in the standard model to be at percent level. We consider then two scenarios beyond the standard model, the model with an extra vector-like down quark (VLDQ) and the R-parity violating supersymmetric model (RPV) and show that the direct CP violating asymmetry in B+→ϕK+ could be as large as ~ 85% (70%) in VLDQ (RPV) model.

A MEASUREMENT OF THE BRANCHING FRACTION OF THE EXCLUSIVELY DECAY B0→ K*0γ

The exclusive decay B0→ K*0γ proceeds via the b → sγ electroweak penguin diagram. This process can be used to probe the electroweak couplings of the top quark as well as any new physics that could also mediate the process. Using (8.6± 0.3) × 106 decays, we obtain a preliminary branching fraction measurement of the decay B0 → K*0γ of ℬ(B0 → K*0γ)= (5.42 ± 0.82 ± 0.47) × 10-5.