arXiv subjects

Yu-Feng Zhou

Publications and source records attributed to Yu-Feng Zhou.

90 records · Page 5Linked to original sources

arXiv2006

Implications of new data in charmless B decays

Based on the latest experimental data of $B \to ππ$ and $πK$ modes, a model-independent analytical analysis is presented. The CP-averaged branching ratio difference $ΔR = R_c - R_n$ in $B\to πK$ decays with $R_c = 2Br(π^0K^-)/Br(π^-\bar{K}^0)$ and $R_n =Br(π^+K^-)/2Br(π^0\bar{K}^0)$ is reduced though it remains larger than the prediction from the standard model(SM) as both measured $R_n$ and $R_c$ are enhanced, which indicates that a room for new physics becomes smaller. The present data of $ππ$ decay reduce the ratio $|C/T|$ from the previous value of $|C/T|\simeq 0.8 $ to $|C/T| \simeq 0.65$, which is still larger than the theoretical estimations based on QCD factorization and pQCD. Within SM and flavor SU(3) symmetry, the current $πK$ data also diminish the ratio $|C'/T'|$ from the previous value $|C'/T'| \simeq 2$ to $|C'/T'| \simeq 1.16$ with a large strong phase $δ_{C'} \simeq -2.65$, while its value remains much larger than the one extracted from the $ππ$ modes. The direct CP violation $A_{CP}(π^0\bar{K}^0)$ is predicted to be $A_{CP}(π^0\bar{K}^0) = -0.15\pm0.03$, which is consistent with the present data. Two kinds of new effects in both strong and weak phases of the electroweak penguin diagram are considered. It is found that both cases can reduce the ratio to $|C'/T'| = 0.40\sim 0.80$ and lead to roughly the same predictions for CP violation in $π^0 K^0$.

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arXiv2006

Signal of New Physics and Test of Isospin-SU(3) Relations and CP Violation in Charmless B Decays

A model-independent analytical analysis for charmless B decays is presented. It is demonstrated that the CP-averaging branching ratio difference $ΔR = R_c - R_n$ in $B\to πK$ decays with $R_c = 2Br(π^0K^-)/Br(π^-\bar{K}^0)$ and $R_n =Br(π^+K^-)/2Br(π^0\bar{K}^0)$ defines a sensitive quantity for probing new physics as $ΔR$ is dominated by the second order of electroweak penguin contributions. A large discrepancy between experimental data and standard model (SM) prediction $ΔR^{exp}/ΔR^{SM} > 9.0\pm 5.0$ strongly indicates a signal of new physics in the electroweak penguin sector. Within the SM, the current $πK$ data favor a very large color-suppressed tree amplitude $|C'/T'|\sim 2$, large CP violations ($A_{CP}(π^0\bar{K}^0)\sim 0.69$ and $A_{CP}(π^0\bar{K}^-)\sim 0.56$), which is connected to $ΔR$ and be solved simultaneously with extra electroweak penguin contributions. More accurate measurements on the ratio difference $ΔR$ and CP violation in $B\to ππ, πK$ decays may provide a window for probing new physics and testing the isospin and SU(3) symmetries.

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arXiv2006

Determining weak phase gamma and probing new physics in b->s transitions from B->eta(eta')K

We present a method of determining weak phase γin the Cabibbo-Kobayashi-Maskawa matrix from decays B->ηK, η' K$ alone. Given a large ratio between color-suppressed and color-allowed tree diagrams extracted from global ππ(K) fits, γis determined from the current data of η' K and the result is in agreement with the global Standard Model(SM) fits. However, a smaller ratio from factorization based calculations gives $γ\sim 90^\circ$. New physics beyond the SM can be singled out ifγobtained in η^{(')} K modes is significantly different than the ones from other modes or other approaches. The effective value of γfrom η' K is very sensitive to new physics contributions and can be used to extract new physics parameters for a class of models which do not give contributions to strong phases significantly.

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arXiv2005

Charmless decays B->pipi, piK and KK in broken SU(3)symmetry

Charmless B decay modes $B \to ππ, πK$ and $KK$ aresystematically investigated with and without flavor SU(3) symmetry. Independent analyses on $ππ$ and $πK$ modes both favor a large ratio between color-suppressed tree ($C$) and tree ($T)$ diagram, which suggests that they are more likely to originate from long distance effects. The sizes of QCD penguin diagrams extracted individually from $ππ$, $πK$ and $KK$ modes are found to follow a pattern of SU(3) breaking in agreement with the naive factorization estimates. Global fits to these modes are done under various scenarios of SU(3)relations. The results show good determinations of weak phase $γ$ in consistency with the Standard Model (SM), but a large electro-weak penguin $(P_{\tmop{EW}})$ relative to $T + C$ with a large relative strong phase are favored, which requires an big enhancement of color suppressed electro-weak penguin ($P_{\tmop{EW}}^C$) compatible in size but destructively interfering with $P_{\tmop{EW}}$ within the SM, or implies new physics. Possibility of sizable contributions from nonfactorizable diagrams such as $W$-exchange ($E$), annihilation($A$) and penguin-annihilation diagrams($P_A$) are investigated. The implications to the branching ratios and CP violations in $K K$modes are discussed.

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arXiv2005

Exploring Final State Hadron Structure and SU(3) Flavor Symmetry Breaking Effects in D->PP and D->PV Decays

The nonleptonic two body decays $D\to PP$ and $D\to PV$ are investigated based on the diagrammatic decomposition in a generalized factorization formalism. It is shown that to fit the experimental data, the SU(3) flavor symmetry breaking effects of the coefficients $a_i$s should be considered in $D\to PP$ decay modes. In $D\to PV$ decays, the final state hadron structure due to the pseudoscalar and vector mesons has more important effects on the coefficients $a_i$s than the SU(3) symmetry breaking effects. It is found that the nonfactorizable contributions as well as that of the exchange and annihilation diagrams are significant in these decays.

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arXiv2005

Higgs physics and CP violation

The CP violation in $K$ and B decays are discussed with the emphasize on the precise prediction for $ε'/ε$ and the new physics effects from a class of models with additional Higgs doublets and fermions. The contributions from standard model with two-Higgs-doublet (S2HDM) to $K$, $B$ mixing and decays are briefly reviewed. The possible large effects on CP violation in $B\to ϕK$ is discussed in an extended standard model with both an additional Higgs doublet and fourth generation quarks (S2HDM4). We show that although the S2HDM and the Standard model with fourth generation quarks alone are not likely to largely change the effective $\sin 2β$ from the decay of $B \to ϕK_S $, the S2HDM4 model can easily account for the possible large deviation of $\sin 2 β$ without conflicting with other experimental constraints.

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arXiv2005

Implications of Charmless B Decays with Large Direct CP Violation

Based on the most recent data in charmless B decays including the very recently reported large direct CP violations, it is shown that the weak phase gamma can well be extracted without two-fold ambiguity even only from two decay modes pi^+pi^- and pi^+K^-, and its value is remarkably consistent with the global standard model fit at a compatible accuracy. A fit to all the pi pi, pi K data favor both large electroweak penguin and color-suppressed tree amplitude with large strong phases. It is demonstrated that the inclusion of small SU(3)symmetry breaking effects of strong phases and the inelastic rescattering effects can well improve the consistency of the data, while both effects may not be sufficient to arrive at a small electroweak penguin amplitude in the standard model. It is of interest to notice that large or small electroweak penguin amplitude becomes a testable prediction as they lead to significantly different predictions for the direct CP violations for pi^0 pi^0, pi^0 K^0 modes. Clearly, precise measurements on charmless B decays will provide a window for probing new physics.

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arXiv2004

Vector Meson Contributions in epsilon'/epsilon

The CP violating parameter epsilon'/epsilon is computed using the low-energy dynamics of a chiral theory supplemented by vector resonances. The divergent contributions coming from strong pi-pi scattering are tamed by vector-meson exchange terms. This amounts to softening the fast growing high-energy behaviour of pi-pi scattering. The final result for epsilon'/epsilon shows a smooth dependence on the cut-off where low energy dynamics is matched with that of QCD.

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arXiv2004

CP asymmetry in $B \to ϕK_S$ in a general two-Higgs-doublet model with fourth-generation quarks

We discuss the time-dependent CP asymmetry of decay $B \to ϕK_S$ in an extension of the Standard Model with both two Higgs doublets and additional fourth-generation quarks. We show that although the Standard Model with two-Higgs-doublet and the Standard model with fourth generation quarks alone are not likely to largely change the effective $\sin 2 β$ from the decay of $B \to ϕK_S $, the model with both additional Higgs doublet and fourth-generation quarks can easily account for the possible large negative value of $\sin 2 β$ without conflicting with other experimental constraints. In this model, additional large CP violating effects may arise from the flavor changing Yukawa interactions between neutral Higgs bosons and the heavy fourth generation down type quark, which can modify the QCD penguin contributions. With the constraints obtained from $b \to s \bar{s} s$ processes such as $B \to X_s γ$ and $Δm_{B_s^0}$, this model can lead to the effective $\sin 2 β$ to be as large as $- 0.4$ in the CP asymmetry of $B \to ϕK_S$.

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arXiv2004

More Precise Determination of V_{cb} & V_{ub} and Direct CP Violation in Charmless B Decays

More precise extractions on the two important CKM matrix elements $|V_{cb}|$ and $|V_{ub}|$ are presented up to $1/m_Q^2$ corrections based on the complete heavy quark effective field theory (HQEFT) of QCD. The HQEFT as a large component QCD provides us a complete theoretical framework for correctly and systematically evaluating the subleading and higher order contributions in $1/m_Q$ expansion of heavy quarks. A global analysis on charmless B decays is made based on the isospin and SU(3) flavor symmetry. An isospin relation is found to be very useful for studying SU(3) symmetry breaking effects of strong phases and exploring new type of electroweak penguin effects. The direct CP violation in charmless B decays is predicted and its precise measurement is helpful either for testing SU(3) symmetry breaking effects of strong phases or for probing new physics beyond standard model.

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arXiv2003

Textures and hierarchies in quark mass matrices with four texture-zeros

A systematic analysis on the phenomenologically allowed textures in Hermitian quark mass matrices with four texture-zeros is presented. The current data allow a full determination of the mass matrix elements, provided that the actual number of the parameters in the matrices is less than or equal to ten. Besides the standard texture with zeros located in (1,1) and (1,3) positions, we find four new type of parallel mass matrices. All of them are found to have similar hierarchical structures: three of the nonzero matrix elements are at the same order of magnitude with a small geometric hierarchy, while the remaining one is relatively much smaller. These textures show a possibility that a realistic quark mass matrix may have an approximate flavor $S(2)_{L}\otimes S(2)_{R}$ symmetry, i.e. a partial flavor democracy. The absolute values of the CP violating phases in the matrix elements are found to be either close to their maximum ($\approx 90^\circ$) or very small ($\leq 10^{\circ}$). We also find twenty-six quasi-parallel and seventeen non-parallel textures allowed by the experimental data.

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arXiv2003

Isospin relation and SU(3) breaking effects of strong phases in Charmless B decays

Isospin and flavor SU(3) relations in charmless hadronic B decays $B\to ππ, πK$ are investigated in detail with paying attention to the SU(3) symmetry breaking effects in both amplitudes and strong phases. In general, the isospin and the flavor SU(3) structure of the effective Hamiltonian provide several relations among the amplitudes and strong phases. Whereas a global fit to the latest data shows that some relation seems not to be favorable for a consistent explanation to the current data within the standard model (SM). By considering several patterns of SU(3) breaking, the amplitudes and the corresponding strong phases are extracted and compared with the theoretical estimations. It is found that in the case of SU(3) limits and also the case with SU(3) breaking only in amplitudes, the fitting results lead to an unexpected large ratio between two isospin amplitudes $a^{c}_{3/2}/a^{u}_{3/2}$, which is about an order of magnitude larger than the SM prediction. The results are found to be insensitive to the weak phase $γ$. By including SU(3) breaking effects on the strong phases, one is able to obtain a consistent fit to the current data within the SM, which implies that the SU(3) breaking effect on strong phases may play an important role in understanding the observed charmless hadronic B decay modes $B\to ππ$ and $πK$. It is possible to test those breaking effects in the near future from more precise measurements of direct CP violation in B factories.

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arXiv2003

Texture of Yukawa coupling matrices in general two-Higgs-doublet model

We discuss possible parallel textures of the Yukawa coupling matrices in the generaltwo-Higgs-doublet model (2HDM). In those textures the flavor changing neutral currentsare naturally suppressed. Motivated by a phenomenologically successful texturewith four texture zeros in the standard model, we propose a predictive ansatz for the Yukawa coupling matrices with the same texture in the general 2HDM. Compared with the six texture-zero based ansatz proposed by Cheng and Sher, it is in a better agreement with the data of quark mixings and CP violation. The four texture-zero based ansatz predicts a different hierarchy in the Yukawa coupling matrix elements. As a consequence, in the lepton sector, the related Yukawa couplings are less constrained by the experimental upper bound of $μ\to eγ$, which allows significantly larger predictions for other processes. The contributions from neutral scalar interactions to the lepton number violation decay modes $\ell\to \ell_{1}\ell_{2}\ell_{3}$ are calculated in both ansatz. It is shown that the predictions from the four texture-zero based ansatz could be two order of magnitude greater than that from the six texture-zero based one. The branching ratio of $μ\to 3e$ and $τ\to 3μ$ can reach $7.5 \times 10^{-17}$ and $1.3\tiems 10^{-10}$ respectively. The predicted ratio of $Br(μ\to 3e)/Br(τ\to 3e)$ is also larger and almost parameter independent. Those differences make the two ansatz to be easily distinguished by the future experiments.

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arXiv2003

The gluonic B and J/psi decays into the eta' meson

The inclusive and exclusive B decays into the eta' meson plus others are investigated in a model based on the QCD anomaly. The invariant mass distribution is discussed. The constraint of the effective coupling is obtained from the data of the exclusive decay modes. The branching ratio of J/psi -> eta'eta gamma is predicted to be as large as 5.4*10^{-5}, which can be tested in the forthcoming CLEO-c experiments.

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arXiv2001

Muon anomalous magnetic moment in the standard model with two Higgs doublets

The muon anomalous magnetic moment is investigated in the standard model with two Higgs doublets (S2HDM) motivated from spontaneous CP violation. Thus all the effective Yukawa couplings become complex. As a consequence of the non-zero phase in the couplings, the one loop contribution from the neutral scalar bosons could be positive and negative relying on the CP phases. The interference between one and two loop diagrams can be constructive in a large parameter space of CP-phases. This will result in a significant contribution to muon anomalous magnetic moment even in the flavor conserving process with a heavy neutral scalar boson ($m_h \sim$ 200 GeV) once the effective muon Yukawa coupling is large ($|ξ_μ|\sim 50$). In general, the one loop contributions from lepton flavor changing scalar interactions become more important. In particular, when all contributions are positive in a reasonable parameter space of CP phases, the recently reported 2.6 sigma experiment vs. theory deviation can be easily explained even for a heavy scalar boson with a relative small Yukawa coupling in the S2HDM.

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arXiv2001

Implications from recent measurements on sin 2βand muon g-2

The recent data on CP asymmetry in $B->J/ΨK_S$ and muon g-2 are discussed in the framework of standard model and beyond. Possible new phase effects besides the CKM phase are discussed in the processes concerning CP violation in B decays and muon anomalous magnetic moment (muon g-2). It is found that the new phases will result in difference between angles $beta$ measured from $B->J/ΨK_S$ and the one from global fit. The ration between them serves as a probe of not only new physics but also new phase besides the CKM phase In the case of muon g-2, the new phase may change the interferences between various contributions. By including the new phases, some cancelations in the real coupling cases can be avoided and the large value of muon g-2 observed in the recent measurements can be understood.

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arXiv2001

Implication of $\sin 2β$ from global fit and $B\to J/ψK_S$

The measurement of $\sin 2 β$ is discussed within and beyond the standard model. In the presence of new physics, the angle $β$ extracted from the global fit(denoted by $β^{SM}_{fit}$) and the one extracted from $B\to J/ψK_S$ (denoted by $β_{J/ψ}$) are in general all different from the 'true' angle $β$ which is the weak phase of CKM matrix element $V^*_{td}$. Possible new physics effects on the ratio $R_β=\sin2β_{J/ψ}/\sin 2β^{SM}_{fit}$ is studied and parameterized in a most general form. It is shown that the ratio $R_β$ may provide a useful tool in probing new physics. The experimental value of $R_β$ is obtained through an update of the global fit of the unitarity triangle with the latest data and found to be less than unity at 1$σ$ level. The new physics effects on $R_β$ from the models with minimum flavor violation (MFV) and the standard model with two-Higgs-doublet (S2HDM) are studied in detail. It is found that the MFV models seem to give a relative large value $R_β\geq 1$. With the current data, this may indicate that this kind of new physics may be disfavored and alternative new physics with additional phases appears more relevant. As an illustration for models with additional phase beyond CKM phase, the S2HDM effects on $R_β$ are studied and found to be easily coincide with the data due to the flavor changing neutral Higgs interaction.

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arXiv2000

Weak Phase $γ$ and Strong Phase $δ$ from CP Averaged $B\to ππ$ and $πK$ Decays

Assuming SU(3) symmetry for the strong phases in the four decay modes $B\rarrow π^-π^+, π^0 π^+, π^- K^+, π^- \bar{K}^0$ and ignoring the relative small electroweak penguin effects in those decays, the weak phase $γ$ and the strong phase $δ$ can be determined in a model independent way by the CP-averaged branching ratios of the four decay modes. It appears that the current experimental data for $B\to ππ$ and $πK$ decays prefer a negative value of $\cosγ\cosδ$. By combining with the other constraints from $V_{ub}$, $B^{0}_{d,s}-\bar{B}^{0}_{d,s}$ mixings and indirect CP-violating parameter $ε_K$ within the standard model, two favorable solutions for the phases $γ$ and $δ$ are found to lie in the region: $35^{\circ}\altγ\alt 62^{\circ}$ and $106^{\circ}\alt δ\alt 180^{\circ}$ or $86^{\circ}\altγ\alt 151^{\circ}$ and $0^{\circ}\altδ\alt 75^{\circ} $ within 1$σ$ standard deviation. It is noted that if allowing the standard deviation of the data to be more than 1$σ$, the two solutions could approach to one solution with a much larger region for the phases $γ$ and $δ$. Direct CP asymme try $a_{ε''}^{(π^- K^+)}$ in $B\rarrow π^-K^+$ decay can be as large as the present experimental upper bound. Direct CP asymmetry $a_{ε''}^{(π^+π^-)}$ in $B\rarrow π^-π^+$ decay can reach up to about 40% at 1$σ$ level.

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