Seungwon Baek

Is there still a B→πK puzzle?

Abstract We perform a fit to the 2006 B → π K data and show that, when one includes (reasonable) theoretical input, there is a disagreement with the Standard Model. That is, the B → π K puzzle is still present. In fact, it has gotten worse than in earlier years. Assuming that one new-physics (NP) operator dominates, we show that a good fit is obtained only when one type of NP is added (this includes a modification of the electroweak penguin amplitude). The NP amplitude must be sizeable, with a large weak phase.

Bs−B̄s mixing in the MSSM scenario with large flavor mixing in the LL/RR sector

We show that the recent measurements of Bs−s mass difference, Δms, by DO and CDF collaborations give very strong constraints on MSSM scenario with large flavor mixing in the LL and/or RR sector of down-type squark mass squared matrix. In particular, the region with large mixing angle and large mass difference between scalar strange and scalar bottom is ruled out by giving too large Δms. The allowed region is sensitive to the CP violating phases δL(R). The Δms constraint is most stringent on the scenario with both LL and RR mixing. We also predict the time-dependent CP asymmetry in Bs→ψ decay and semileptonic asymmetry in Bs→lX decay.

Bs0–B¯s0 mixing in leptophobic Z′ model

Leptophobic Z^prime gauge boson appears naturally in many grand unified theories, such as flipped SU(5) or string-inspired E_6 models. This elusive particle easily escapes the direct/indirect detections because it does not couple to charged leptons. However, it can generate flavor changing neutral current at tree level. In this letter, we show that the recently measured mass difference, Delta m_s, in the B_s^0 -bar{B}_s^0 system improves the previous bound of flavor changing effective coupling by about one order of magnitude, i.e irrespective of its phase, |U_{sb}^{Z^prime}| leq 0.036 for M_{Z^prime} = 700 GeV, and |U_{sb}^{Z^prime}| leq 0.051 for M_{Z^prime} = 1 TeV.

New physics in B→ππ and B→πK decays

We perform a combined analysis of B→ππ and B→πK decays with the current experimental data. Assuming SU(3) flavor symmetry and no new physics contributions to the topological amplitudes, we demonstrate that the conventional parametrization in the Standard Model (SM) does not describe the data very well, in contrast with a similar analysis based on the earlier data. It is also shown that the introduction of smaller amplitudes and reasonable SU(3) breaking parameters does not improve the fits much. Interpreting these puzzling behaviors in the SM as a new physics (NP) signal, we study various NP scenarios. We find that when a single NP amplitude dominates, the NP in the electroweak penguin sector is the most favorable. However, other NP solutions, such as NP residing in the QCD-penguin sector and color-suppressed electroweak penguin sector simultaneously, can also solve the puzzle.We perform a combined analysis of

Supersymmetric contributions to B0s → K+K-

B to pi pi

B_s^0 - \bar{B}_s^0 Mixing in Leptophobic Z^\prime Model

and

Bs-->K+K- and Bs-->K0 anti-K0 Decays within Supersymmetry

B to pi K

Bs0–B¯s0 mixing in leptophobic Z′Z′ model

decays with the current experimental data. Assuming SU(3) flavor symmetry and no new physics contributions to the topological amplitudes, we demonstrate that the conventional parametrization in the Standard Model (SM) does not describe the data very well, in contrast with a similar analysis based on the earlier data. It is also shown that the introduction of smaller amplitudes and reasonable SU(3) breaking parameters does not improve the fits much. Interpreting these puzzling behaviors in the SM as a new physics (NP) signal, we study various NP scenarios. We find that when a single NP amplitude dominates, the NP in the electroweak penguin sector is the most favorable. However, other NP solutions, such as NP residing in the QCD-penguin sector and color-suppressed electroweak penguin sector simultaneously, can also solve the puzzle.

New physics in B ! and B ! K decays

Inspired by the existing calculation of B->piK decays in supersymmetry (SUSY), we evaluate the dominant SUSY contributions to Bs->K+K-. We show that the observables of this process can be significantly modified in the presence of SUSY. In particular, the branching ratio can be increased considerably compared to the prediction of the standard model (SM). The effect is even more dramatic for the CP-violating asymmetries A_dir and A_mix. These asymmetries, expected to be small in the SM (A_dir is predicted to take only positive values), change drastically with SUSY contributions. The measurement of these observables can therefore be used to detect the presence of physics beyond the SM, and put constraints on its parameters.

Bs0→K+K− and Bs0→K0K̄0 decays within supersymmetry

Leptophobic Z^prime gauge boson appears naturally in many grand unified theories, such as flipped SU(5) or string-inspired E_6 models. This elusive particle easily escapes the direct/indirect detections because it does not couple to charged leptons. However, it can generate flavor changing neutral current at tree level. In this letter, we show that the recently measured mass difference, Delta m_s, in the B_s^0 -bar{B}_s^0 system improves the previous bound of flavor changing effective coupling by about one order of magnitude, i.e irrespective of its phase, |U_{sb}^{Z^prime}| leq 0.036 for M_{Z^prime} = 700 GeV, and |U_{sb}^{Z^prime}| leq 0.051 for M_{Z^prime} = 1 TeV.