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 − .

A tale of invisibility: constraints on new physics in b → sνν

The Belle II experiment will measure the rare decays B → Kνν and B → K∗νν with increased sensitivity which can hence be expected to serve as a very efficient probe of new physics. We calculate the relevant branching ratios in low-energy effective field theory (LEFT) including an arbitrary number of massive sterile neutrinos and discuss the expected sensitivity to the different operators. We also take into account the longitudinal polarisation fraction FL and the inclusive decay rate B → Xsνν. In our investigation we consider new physics dominantly contributing to one and two operators both for massless and massive (sterile) neutrinos. Our results show a powerful interplay of the exclusive decay rates B → Kνν and B → K∗νν, and a surprisingly large sensitivity of the inclusive decay mode to vector operators even under conservative assumptions about its uncertainty. Furthermore, the sensitivity of FL is competitive with the branching ratio of B → K∗νν in the search for new physics contributing to scalar operators and thus also complementary to B → Kνν and B → Xsνν.

Angular analysis of the decay B+ → K∗(892)+μ+μ− in proton-proton collisions at $$ \sqrt{\mathrm{s}} $$ = 8 TeV

Angular distributions of the decay B+→ K∗(892)+μ+μ− are studied using events collected with the CMS detector in $$ \sqrt{\mathrm{s}} $$ s = 8 TeV proton-proton collisions at the LHC, corresponding to an integrated luminosity of 20.0 fb−1. The forward-backward asymmetry of the muons and the longitudinal polarization of the K∗(892)+ meson are determined as a function of the square of the dimuon invariant mass. These are the first results from this exclusive decay mode and are in agreement with a standard model prediction.

Final state interaction effects in B+→Ds*+ ϕ decay

In this article the exclusive decay of [Formula: see text] is calculated using the QCD factorization (QCDF) method and final state interaction (FSI). First, the [Formula: see text] decay is calculated via the QCDF method and only the annihilation graphs exist in that method. The result found using the QCDF method is lower than the experimental result. FSI is considered to solve the [Formula: see text] decay. For this decay, D+K0, D0K+, and [Formula: see text] via the exchange of K0, K+, and [Formula: see text] are chosen for the intermediate states and we calculate B+ → D+K0 → [Formula: see text] decay. The amplitude of B+ → D+K0 decay is calculated using the QCDF method again. The experimental branching ratio of [Formula: see text] decay is less than 1.2 × 10−5 and our results calculated using the QCDF method and FSI are (0.4 ± 0.06) × 10−7 and (0.93 ± 0.08) × 10−5, respectively.

Final State Interaction Effects on theB+→J/ψρ+Decay

The exclusive decay ofB+→J/ψρ+is studied in the framework of the QCD factorization (QCDF) method and final state interaction (FSI). A directB+→J/ψρ+decay is only occurred via a tree and a penguin based on the quark diagram analysis. The result that is found by using the QCDF method is less than the experimental result, so, the role of FSI is considered. The intermediate statesD+D̅0,D+*D̅0*,D+*D̅0, andD+D̅0*via the exchange ofD-andD-*are contributed to theB+→J/ψρ+decay. The above intermediate states is calculated by using the QCDF method. In the FSI effects the results of our calculations depend on “η” as the phenomenological parameter. The range of this parameter are selected from 1 to 2. For the exchanged particlesD-andD-*, it is found that ifη=1.58~1.83is selected the numbers of the branching ratio are placed in the experimental range. The experimental branching ratio ofB+→J/ψρ+decay is(5±0.8)×10-5, and our prediction number is(1.42±0.36)×10-5in the absence of FSI effects, and it becomes(4.2~5.8)×10-5when FSI contributions are taken into account.