arXiv subjects

Seungwon Baek

Publications and source records attributed to Seungwon Baek.

At least 73 records · Page 4Linked to original sources

arXiv2009

Diagnostic for new physics in $B \to πK$ decays

A recent analysis of $B \to πK$ decays concludes that present data do not clearly indicate whether (i) the standard model (or $ΔI=0$ new physics) is sufficient, or (ii) $ΔI=1$ new physics is needed. We show that these two possibilities can be distinguished by whether a sum rule relating the CP asymmetries of the four $B \to πK$ decays is valid. If case (i) is favored, the sum rule holds, and one predicts $A_{CP}(π^0 K^0) = -0.15$, while in case (ii) fits to new physics involving large values of a color-suppressed tree amplitude entail $A_{CP}(π^0 K^0) = -0.03$. The current experimental average $A_{CP}(π^0 K^0) = -0.01 \pm 0.10$ must be measured a factor of at least three times more precisely in order to distinguish between the two cases.

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arXiv2009

The B -> pi K Puzzle: 2009 Update

The measurements of B -> pi K decays have been in disagreement with the predictions of the Standard Model (SM) for some time. In this paper, we perform an update of this puzzle using the latest (2008) data. We find that the situation has become far less clear. A fit to the B -> pi K data alone suggests the presence of new physics (NP). Indeed, if one adds a constraint on the weak phase gamma coming from independent measurements -- the SM fit -- one finds that the fit is poor. On the other hand, it is not terrible. If one is willing to accept some deficiencies in the fit, it can be argued that the SM can explain the B -> pi K data. If one assumes NP, it is found to be present only in the electroweak penguin amplitude, as before. However, the fit is fair at best, and the improvement over the SM is not particularly strong. All and all, while the B -> pi K puzzle has not disappeared, it has become weaker.

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arXiv2008

B_s^0-\bar{B}_s^0 mixing and B -> πK decays in stringy leptophobic Z^\prime

We consider a leptophobic Z^\prime scenario in a flipped SU(5) grand unified theory obtained from heterotic string theory. We show that the allowed Z^\prime mass, flavor conserving and flavor changing couplings of the Z^\prime to the down-type quarks are strongly constrained by the mass difference in B_s-\bar{B}_s system and the four branching ratios of B -> πK decays. It is shown that even under these constraints large deviations in direct and/or indirect CP asymmetries of B \to πK decays from the SM expectations are allowed. Especially it is possible to accommodate the apparent puzzling data in B -> πK CP asymmetries.

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arXiv2008

The B-->pi K Puzzle and Supersymmetry

At present, there are discrepancies between the measurements of several observables in B-->pi K decays and the predictions of the standard model (the ``B-->pi K puzzle''). Although the effect is not yet statistically significant -- it is at the level of $\gsim 3σ$ -- it does hint at the presence of new physics. In this paper, we explore whether supersymmetry (SUSY) can explain the B-->pi K puzzle. In particular, we consider the SUSY model of Grossman, Neubert and Kagan (GNK). We find that it is extremely unlikely that GNK explains the B-->pi K data. We also find a similar conclusion in many other models of SUSY. And there are serious criticisms of the two SUSY models that do reproduce the B-->pi K data. If the B-->pi K puzzle remains, it could pose a problem for SUSY models.

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arXiv2007

$B_s-\bar{B}_s$ mixing and $B_s \to KK$ decays within supersymmetry

We consider the constraint of $B_s-\bar{B}_s$ mass difference, $Δm_s$, on an MSSM scenario with large flavor mixing. Even with this constraint, we show that a large deviation from the SM in CP asymmetries of $B_s \to KK$ decays is still possible, making this channel promising in search for supersymmetry.

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arXiv2007

A solution to B --> pi pi puzzle and B --> K K

The large ratio of color-suppressed tree amplitude to color-allowed one in $B \to ππ$ decays is difficult to understand within the Standard Model, which is known as the "$B \to ππ$ puzzle". The two tree diagrams contain the up- and charm-quark component of penguin amplitude, $P_{uc}$, which cannot be separated by measuring $B \to ππ$ decays alone. We show that the measurements of the branching ratio and direct CP asymmetry of $B^+ \to K^+ \bar{K^0}$ decay enable one to disentangle the $P_{uc}$ with two-fold ambiguity. One of the two degenerate solutions of the $P_{uc}$ can solve the $B \to ππ$ puzzle by giving $|C/T|\sim 0.3$ which is consistent with the expectation in the Standard Model. We also show that the two solutions can be discriminated by the measurement of the indirect CP-asymmetry of $B^0 \to K^0 \ol{K^0}$. We point out that if the $B \to ππ$ puzzle is solved in this way, the corresponding puzzle in $B \to πK$ decays should have a different origin.

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arXiv2007

Is There Still a B -> pi K Puzzle?

We perform a fit to the 2006 B -> pi K data and show that there is a disagreement with the standard model. That is, the B -> pi 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 the electroweak penguin amplitude is modified. The NP amplitude must be sizeable, with a large weak phase.

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arXiv2006

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

We compute the supersymmetric (SUSY) contributions to the observables in Bs-->K+K- and Bs-->K0 anti-K0 decays. The hadronic parameters in the standard-model (SM) amplitudes are obtained from the Bd-->K0 anti-K0 decay using a recent approach that combines flavor SU(3) symmetry and a controlled input from QCD factorization. The latest experimental data for BR(Bs-->K+K-) is in agreement with the SM prediction. We study how the branching ratios and the direct and mixing-induced CP asymmetries of both Bs-->KK decay modes are affected with the inclusion of SUSY, after imposing constraints from BR(B--> Xs gamma), B--> pi K and Delta Ms over the parameter space. While the branching ratios remain unaffected by SUSY, we identify the CP asymmetries of the Bs-->KK decays as the most promising observables to look for large deviations from the SM.

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arXiv2006

B_s^0 - \bar{B}_s^0 Mixing in Leptophobic Z^\prime 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, Δm_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.

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arXiv2006

B_s - \bar{B}_s mixing in the MSSM scenario with large flavor mixing in the LL/RR sector

We show that the recent measurements of $B_s-\bar{B}_s$ mass difference, $Δm_s$, by DØ 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 $Δm_s$. The allowed region is sensitive to the CP violating phases $δ_{L(R)}$. The $Δm_s$ constraint is most stringent on the scenario with both LL and RR mixing. We also predict the time-dependent CP asymmetry in $B_s \to ψϕ$ decay and semileptonic asymmetry in $B_s\to \ell X$ decay.

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arXiv2006

New physics in $B \to ππ$ and $B \to πK$ decays

We perform a combined analysis of $B \to ππ$ and $B \to πK$ 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.

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arXiv2006

Supersymmetric Contributions to Bs->K+K-

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.

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arXiv2005

Polarization States in B -> rho K* and New Physics

The standard-model explanations of the anomalously-large transverse polarization fraction fT in B -> phi K* can be tested by measuring the polarizations of the two decays B+ -> rho+ K*0 and B+ -> rho0 K*+. For the scenario in which the transverse polarizations of both B -> rho K* decays are predicted to be large, we derive a simple relation between the fT's of these decays. If this relation is not confirmed experimentally, this would yield an unambiguous signal for new physics. The new-physics operators which can account for the discrepancy in B -> pi K decays will also contribute to the polarization states of B -> rho K*. We compute these contributions and show that there are only two operators which can simultaneously account for the present B -> pi K and B -> rho K* data. If the new physics obeys an approximate U-spin symmetry, the B -> phi K* measurements can also be explained.

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arXiv2005

Measurements of New Physics in B -> pi pi Decays

If new physics (NP) is present in B -> pi pi decays, it can affect the isospin I=2 or I=0 channels. In this paper, we discuss various methods for detecting and measuring this NP. The techniques have increasing amounts of theoretical hadronic input. If NP is eventually detected in B -> pi pi -- there is no evidence for it at present -- one will be able to distinguish I=2 and I=0, and measure its parameters, using these methods.

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arXiv2005

$B_s \to μ^+ μ^-$ and the upward-going muon flux from the WIMP annihilation in the sun or the earth

We consider the upward-going muon flux due to the WIMP annihilations in the cores of the sun and the earth, including the upper bound on the branching ratio for $B_s \to μ^+ μ^-$ decay. We find that the constraint from $B_s \to μ^+ μ^-$ is very strong in most parameter space, and exclude the supergravity parameter space regions where the expected upward-going muon fluxes are within the expected reach of AMANDA II.

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arXiv2005

Can one detect new physics in I=0 and/or I=2 contributions to the decays B --> pi pi?

We study the effects of new-physics contributions to B --> pi pi decays, which can be parametrized as four new complex quantities. A simple analysis is provided by utilizing the reparametrization invariance of the decay amplitudes. We find that six quantities can be reabsorbed into the definitions of Standard Model-like parameters. As a result, the usual isospin analysis provides only two constraints on new physics which are independent of estimates for the Standard Model contributions. In particular, we show that one is not sensitive to new physics affecting the I=0 amplitudes. On the other hand, I=2 new physics can be detected, and its parameters can be measured by using independent determinations of the weak phases. We obtain constraints on these new-physics parameters through a fit to the current experimental data.

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arXiv2005

New-Physics Signals in B -> pi pi Decays

This paper has been withdrawn by the authors, due to a mistake which invalidates the analysis. One can never detect the presence of I=0 new physics in B -> pi pi.

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arXiv2005

B -> pi pi Decays and New Physics

This paper has been withdrawn by the authors, due to a mistake which invalidates the analysis. One can never detect the presence of I=0 new physics in B -> pi pi.

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