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Y. -Y. Keum

Publications and source records attributed to Y. -Y. Keum.

At least 19 recordsLinked to original sources
arXiv2005

CP asymmetry, branching ratios and isospin breaking effects of B -> K* gamma with the perturbative QCD approach

The radiative B -> K* gamma mode is caused by a penguin operator which is a quantum correction. Thus this mode may be useful in the search for physics beyond the standard model. In this paper, we compute the branching ratio, direct CP asymmetry, and isospin breaking effects within the Standard Model in the framework perturbative QCD, and discuss how new physics might show up in this decay.

hep-ph↗
arXiv2004

Phenomenological Applications of $k_T$-Factorization (--Large Direct CP-Asymmetry in B-meson Decays--)

We discuss applications of the perturbative QCD approach in the exclusive non-leptonic two body B-meson decays. We briefly review its ingredients and some important theoretical issues on the factorization approaches. PQCD results are compatible with present experimantal data for the charmless B-meson decays. We predict the possibility of large direct CP asymmetry in $B^0 \to π^{+}π^{-}$ $(23\pm7 %)$ and $B^0\to K^{+}π^{-}$ $(-17\pm5%)$. We also investigate the Branching ratios, CP asymmetry and isopsin symmetry breaking in $B \to (K^*/ρ) γ$ decays and look for the possible new physics contribution via gluino mediation SUSY which can accomodate the large deviation of $S_{ϕK_s}$ from SM.}

hep-ph↗
arXiv2003

CP Violation and Nonleptonic B-meson Decays

We discuss the perturbative QCD approach for exclusive non-leptonic two body B-meson decays. We briefly review its ingredients and some important theoretical issues related to the factorization approach. PQCD results are compatible with present experimental data for the charmless B-meson decays. We predict the possibility of large direct CP violation effects in $B^0 \to π^{+}π^{-}$ $(23\pm7 %)$ and $B^0\to K^{+}π^{-}$ $(-17\pm5%)$. For charmed decay $B \to D^{(*)}π$, we get large non-factorizable contributions for Color-suppressed decays and obtain $|a_2/a_1|\sim 0.4-0.5$ and $Arg(a_2/a_1)\sim -42^{o}$. In the last section we investigate the method to extract the weak phases $ϕ_2$ from $B \to ππ$ decay and $ϕ_3$ from $Kπ$ modes. From BaBar measurement of CP asymmetry for the $π^{+}π^{-}$ decay, the prefered CKM weak phases are: $ϕ_1=(24\pm2)^{o}$, $ϕ_2=(78\pm 22)^{o}$ and $ϕ_3=(78\pm 22)^{o}$.

hep-ph↗
arXiv2002

Dynamically enhanced $B\to K^*π$ decays in perturbative QCD

We investigate the $B \to K^{*}π$ decays, one of hardly understandable processes among charmless B-meson decays, within the perturbative QCD method. Owing to the dynamically enhanced mechanism in PQCD, we obtain large branching ratios and large direct CP asymmetries, for instance, $Br(B^0 \to K^{*\pm}π^{\mp})=(9.1^{+4.9+0.3}_{-3.9-0.2})\times 10^{-6}$, $Br(B^{\pm} \to K^{*0}π^{\pm})=(10.0^{+5.3}_{-3.5}\pm 0.0)\times 10^{-6}$; $Acp(B^0 \to K^{*\pm}π^{\mp})=(-19.2^{+0.5}_{-1.7})%$, and $Acp(B^{\pm} \to K^{*\pm}π^{0})=(-43.7^{+4.0}_{-4.2})%$. The branching ratios are consistent with experimental data and large direct CP violation effects will be tested by near future experimental measurements in Asymmetric B-factory.

hep-ph↗
arXiv2002

A Novel PQCD Approach in Charmless B-meson Decays

We discuss a novel pertubative QCD approach on the exclusive non-leptonic two body B-meson decays. We briefly review its ingredients and some important theoretical issues on the factorization approaches. We show numerical results which is compatible with recent experimantal data for the charmless B-meson decays.

hep-ph↗
arXiv2001

One-loop Neutron Electric Dipole Moment from Supersymmetry without R-parity

We present a detailed analysis together with exact numerical calculations on one-loop contributions to neutron electric dipole moment from supersymmetry without R-parity, focusing on the gluino, chargino, and neutralino contributions. Apart from the neglected family mixing among quarks, complete formulae are given for the various contributions, through the quark dipole operators, to which the present study is restricted. We discuss the structure and main features of the R-parity violating contributions and the interplay between the R-parity conserving and violating parameters. In particular, the parameter combination $μ_i^*λ^{\prime}_{i11}$, under the optimal parametrization adopted, is shown to be solely responsible for the R-parity violating contributions in the supersymmetric loop diagrams. While $μ_i^*λ^{\prime}_{i11}$ could bear a complex phase, the latter is not necessary to have a R-parity violating contribution.

hep-ph↗
arXiv2001

Direct CP Asymmetry of B -> X_d γin the effective SUSY model

We investigate the effect of supersymmetric CP violating phases on the inclusive decay B\to X_dγ. Although such a decay contains a large background from B\to X_sγ, if isolated it may exhibit sizeable CP violation, both in the Standard Model (SM) and in the context of models beyond the SM. With unconstrained supersymmetric CP violating phases we show that the direct CP asymmetry (A_CP) lies in the region -40% \le A_CP \le 40%, where a positive asymmetry would constitute a clear signal of physics beyond the SM. Even if a direct measurement of B\to X_dγproves too dif ficult experimentally, its asymmetry contributes non-negligibly to the measurements of A_CP for B\to X_sγ, and thus should be included in future analyses. We show t hat there may be both constructive and destructive interference between A^dγ_CP and A^sγ_CP.

hep-ph↗
arXiv2001

Effect of Supersymmetric phases on the Direct CP Asymmetry of B -> X_d γ

We investigate the effect of supersymmetric CP violating phases on the inclusive decay B\to X_dγ. Although such a decay contains a large background from B\to X_sγ, if isolated it may exhibit sizeable CP violation, both in the Standard Model (SM) and in the context of models beyond the SM. With unconstrained supersymmetric CP violating phases we show that the direct CP asymmetry (A_CP) lies in the region -40% \le A_CP \le 40%, where a positive asymmetry would constitute a clear signal of physics beyond the SM. Even if a direct measurement of B\to X_dγproves too dif ficult experimentally, its asymmetry contributes non-negligibly to the measurements of A_CP for B\to X_sγ, and thus should be included in future analyses. We show t hat there may be both constructive and destructive interference between A^dγ_CP and A^sγ_CP.

hep-ph↗
arXiv2001

R-parity Violating Contribution to Neutron EDM at One-loop Order

We present the full result for the down squark mass-squared matrix in the complete theory of supersymmetry without R-parity where all kind of R-parity violating terms are admitted without bias. An optimal parametrization, the single-VEV parametrization, is used. The major result is a new contribution to $LR$ squark mixing, involving both bilinear and trilinear R-parity violating couplings. Among other things, the latter leads to neutron electric dipole moment at one-loop level. Similiar mechanism leading to electron electric dipole moment at the same level. We present here a short report on major features of neutron electric dipole moment from supersymmetry without R-parity and give the interesting constraints obtained.

hep-ph↗
arXiv2000

Penguin Enhancement and $B\to Kπ$ decays in perturbative QCD

We compute branching ratios of $B\to Kπ$ decays in the framework of perturbative QCD factorization theorem. Decay amplitudes are classified into the topologies of tree, penguin and annihilation, all of which contain both factorizable and nonfactorizable contributions. These contributions are expressed as the convolutions of hard $b$ quark decay amplitudes with universal meson wave functions. It is shown that (1) matrix elements of penguin operators are dynamically enhanced compared to those employed in the factorization assumption; (2) annihilation diagrams are not negligible, contrary to common belief; (3) annihilation diagrams contribute large strong phases; (4) the uncertainty of current data of the ratio $R={\cal B}(B_d^0\to K^\pmπ^\mp)/{\cal B}(B^\pm\to K^0π^\pm)$ and of CP asymmetries is too large to give a constraint of $ϕ_3$. Assuming $ϕ_3=90^o$ which is extracted from the best fit to the data of $R$, predictions for the branching ratios of the four $B\to Kπ$ modes are consistent with data.

hep-ph↗
arXiv2000

New Physics Search in B Meson Decays

We discuss new physics search within the minimal supergravity model by using a possible large direct CP asymmetry in $B^{\pm} \to K^{\pm}ϕ, K^{0}π^{\pm}$ decays and B meson rare decays.

hep-ph↗
arXiv1999

The non-perturbative corrections to the $\bar B \to X_sγ$ photon spectrum in a parton-like model

We derive a new parton-like formula, which establishes a simple connection between the electroweak decay rate $Γ(\bar B \to X_sγ$) and the rate of a free b-quark decay. The main features of our approach are the treatment of the b-quark as an on-mass-shell particle and the inclusion of the effects arising from the b-quark transverse motion in the $\bar B$-meson. Using various b-quark light-front (LF) distribution functions, both phenomenological one and the ones derived from current constituent quark models, and neglecting perturbative corrections we compute the photon energy spectra and the moments of the shape function. It is shown that the parton-like approach is fully consistent with the Heavy Quark Effective Theory (HQET) provided the b-quark constituent mass is redefined in the way similar to that used in HQET to define the pole mass of the b quark. In this way the correction to first order in $1/m_b$ can be eliminated from the total width in agreement with the general statement of HQET. We have also found that the photon energy spectra calculated in the LF approach agree well with the ones obtained in the ACM model, provided the same distribution function is used as input in both cases. In spite of the simplicity of the model our results show a fair good agreement both with the HQET predictions and available experimental data.

hep-ph↗
arXiv1999

Factorization and Decay Constants $f_{D_s^*}$ and $f_{D_s}$

We calculate the decay constants of $D_s$ and $D_s^{*}$ with $\bar{B}^0 \ra D^{+}\ell^{-}ν$ and $\bar{B}^0 \ra D^{+}D_s^{-(*)}$ decays. In our analysis we take the factorization method including non-factorizable term contributions and used two different form factor behaviours (constant and monopole-type) for $F_0(q^2)$. We also consider the QCD-penguin and Electroweak-penguin contributions in hadronic decays within the NDR renormalization scheme at NLO calculation. We estimate the decay constant of the $D_s$ meson to be $233\pm49$ ${\rm MeV}$ for (pole/pole)-type form factor and $255\pm54$ ${\rm MeV}$ for (pole/constant)-type form factor. For $D_s^{*}$ meson, we get $f_{D_s^{*}} = 346 \pm 82$ ${\rm MeV}$, and $f_{D_s^{*}}/f_{D_s} = 1.43 \pm 0.45$ for (pole/constant)-type form factor.

hep-ph↗
arXiv1999

A short look at epsilon'/epsilon

We analyze the theoretical implications of the new KTeV measurement of direct CP-violation in K->pi pi decays. The result is found consistent with the Standard Model for low values of the strange quark mass m_s. If the hadronic parameters B_6^{(1/2)} and B_8^{(3/2)} satisfy 2 B_6^{(1/2)} - B_8^{(3/2)} < 2, as suggested by lattice and 1/N_c calculations, we find an upper bound of 110 MeV for m_s (2 GeV)$. We parametrize potential new physics contributions to ε'/εand illustrate their correlation with upper bounds on m_s. Finally we discuss a non-perturbative mechanism, which is not contained in the existing calculations of B_6^{(1/2)}. This mechanism enhances B_6^{(1/2)} and thereby leads to a better understanding of the Delta I=1/2 rule and the high measured value of Re (ε^\prime/ε)

hep-ph↗
arXiv1998

Effect of supersymmetric CP phases on the $B \to X_s γ$ and $B \to X_s l^+ l^-$ decays in the minimal supergravity model

We investigate the effect of supersymmetric CP violating phases on the $B\to X_s γ$ and $B\to X_s l^+l^-$ decays in the minimal supergravity model. We show that the phase of the trilinear scalar coupling constant for top squarks is strongly suppressed and aligned to that of the gaugino mass due to a renormalization effect from the Planck scale to the electroweak scale. As a result, the effect of supersymmetric CP violating phases on the $B \to X_s γ$ and $B \to X_s l^+ l^-$ decays are small taking into account the neutron and the electron electric dipole moment constraints. For the $B \to X_sγ$ decay, the amplitude has almost no new CP violating phase and the direct CP asymmetry is less than 2 %. For the $B \to X_s l^+ l^-$ decay, the branching ratio can be sizably different from that in the standard model only when the sign of the $B \to X_s γ$ amplitude is opposite to that in the standard model.

hep-ph↗
arXiv1998

Decay Constants $f_{D_s^*}$ and $f_{D_s}$ from ${\bar{B}}^0\to D^+ l^- {\barν}$ and ${\bar{B}}^0\to D^+ D_s^{-(*)}$ Decays

We calculate the decay constant of $D_s$ and $D_s^{*}$ with $\bar{B}^0 \ra D^{+}\ell^{-}ν$ and $\bar{B}^0 \ra D^{+}D_s^{-(*)}$ decays. In our analysis we assume that factorization ansatz works and used two different form factor behaviours (constant and monopole-type) for $F_0(q^2)$. We also consider the QCD-penguin contributions in hadronic decays within the NDR renormalization scheme at NLO calculation. We estimate the decay constant of the $D_s$ meson to be $219\pm46 MeV$ for (pole/pole)-type form factor and $239\pm50$ $MeV$ for (pole/constant)-type form factor. For $D_s^{*}$ meson, we predict $f_{D_s^{*}} = 336 \pm 79 MeV$, and $f_{D_s^{*}}/f_{D_s} = 1.41 \pm 0.41$ for (pole/constant)-type form factor.

hep-ph↗
arXiv1998

Factorization in Color-Suppressed B Meson Decays

We summerize the status of factorization hypothesis in the color-suppressed B meson decays : $B \to J/ψK^{(*)}$. We present the general formalism for decay rates and polarization fractions with considering all possible non-factorizable contributions which also include the color-octet contributions, and a new factorization scheme comes appear when the universality is exist : $χ_{F1} = χ_{A1} = χ_{A2} = χ_{V} = χ$. We consider various phenomenological models to compare their theoretical predictions with the recent CLEO II experimental measurements.

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