arXiv subjects

Ya-Dong Yang

Publications and source records attributed to Ya-Dong Yang.

At least 91 records · Page 5Linked to original sources

arXiv2010

$B \to K^{\ast} l^+ l^-$, $K l^+ l^-$ decays in a family non-universal $Z^{\prime}$ model

Motivated by the observed forward-backward asymmetry in $B\to K^{\ast} l^+ l^-$ decay, we perform a detailed analysis of this decay mode within a family non-universal $Z^{\prime}$ model. With the related coupling $Z^{\prime}-\bar{s}b$ constrained by $\bar{B}_s-B_s$ mixing, $B\to πK$, and $B\to X_s μ^{+}μ^{-}$ decays, we look for further constraint on the couplings $Z^{\prime}-μ^{+}μ^{-}$ from $A_{FB}(B\to K^{\ast} μ^{+}μ^{-})_{0 {\rm GeV}^2\leqslant q^2\leqslant 2 {\rm GeV}^2}$ and get numerically $B_{μμ}^{L,R}\sim{\cal O}(10^{-2})$. Moreover, we find that the relations, $B_{μμ}^{L}<B_{μμ}^{R}$ and $B_{μμ}^{L}+B_{μμ}^{R}<0$, with a small negative $ϕ_{s}^{L}$, are crucial to moderate the discrepancy for $A_{FB}(B\to K^{\ast} μ^{+}μ^{-})$ between the SM prediction and the experimental data. Numerically, comparing with the SM prediction, we find that $A_{FB}(B\to K^{\ast} μ^{+}μ^{-})_{0 {\rm GeV}^2\leqslant q^2\leqslant 2 {\rm GeV}^2}$ could be enhanced about 80% and 50% by $Z^{\prime}$ contribution at most in scenarios S1 and S2, corresponding to the two fitted results of $ϕ_{s}$ by UTfit collaboration, respectively. However, the results are still about $1.5σ$ lower than the experimental measurement.

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arXiv2010

Family Non-universal Z^\prime effects on \bar{B}_q-B_q$ mixing, B\to X_s μ^+μ^- and B_s\to μ^+μ^- Decays

Motivated by the large discrepancy of CP-violating phase in $\bar{B}_s-B_s$ mixing between the experimental data and the Standard Model prediction, we pursue possible solutions within a family non-universal $Z^{\prime}$ model. Within such a specific model, we find that both the $\bar{B}_s-B_s$ mixing anomaly and the well-known "$πK$ puzzle" could be moderated simultaneously with a nontrivial new weak phase, $ϕ^L_s\sim-72^{\circ}$ (S1) or $-82^{\circ}$ (S2). With the stringently constrained $Z^{\prime}$ coupling $B_{sb}^{L}$, we then study the $Z^{\prime}$ effects on the rare $B\to X_s μ^+μ^-$ and $B_s\to μ^+μ^-$ decays, which are also induced by the same $b\to s$ transition. The observables of $B\to X_s μ^+μ^-$, at both high and low $q^2$ regions, are found to be able to put strong constraints on the $μ-μ-Z^{\prime}$ coupling, $B_{μμ}^{L,R}\sim10^{-2}$. It is also shown that the combined constraints from $\bar{B}_s-B_s$ mixing, $B\to πK$ and $B\to X_s μ^+μ^-$ do not allow a large $Z^{\prime}$ contribution to the pure leptonic $B_s\toμ^+μ^-$ decay.

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arXiv2009

B_s\to K^{()-}K^{()+}, K^{()-}π^{+}, K^{()-}ρ^{+} decays in R-parity violating supersymmetry

With the first measurements of the branching ratios and the direct CP asymmetries of $B_s\to K^{-}K^{+}$, $K^{-}π^{+}$ decays by the CDF collaboration, we constrain the relevant parameter space of the Minimal Supersymmetric Standard Model with R-parity violation. Using the constrained R-parity violating couplings, we further examine their possible effects in $B_{s}\to K^{-*}π^{+}$, $K^{(*)-}ρ^{+}$ and $K^{(*)\pm}K^{(*)\mp}$ decays. We find that some branching ratios and CP asymmetries are very sensitive to the R-parity violating couplings. The direct longitudinal CP asymmetries of tree-dominated process $B_s\to K^{*-}ρ^{+}$ could be enlarged to $\sim 70%$ and the longitudinal polarizations of $B_s\to K^{*-}K^{*+}$, $K^{*-}ρ^{+}$ decays could be suppressed very much by the squark exchange couplings. Near future experiments at CERN LHC can test these predictions and shrink/reveal the parameter spaces of RPV SUSY.

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arXiv2009

Rare decay $π^{0}\to e^+ e^-$ constraints on the light CP-odd Higgs in NMSSM

We constrain the light CP-odd Higgs $A_{1}^{0}$ in NMSSM via the rare decay $π^{0}\to e^{+}e^{-}$. It is shown that the possible $3σ$ discrepancy between theoretical predictions and the recent KTeV measurement of ${\cal B}(π^{0}\to e^+ e^-)$ cannot be resolved when the constraints from $Υ\toγA_1^0$, $a_μ$ and $π^{0}\to γγ$ are combined. Furthermore, the combined constraints also exclude the scenario involving $m_{A_1^0}=214.3$ MeV, which is invoked to explain the anomaly in the $Σ^{+}\to p μ^{+}μ^{-}$ decay found by the HyperCP Collaboration.

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arXiv2009

Constraints on the nonuniversal Z^\prime couplings from B\toπK, πK^{\ast} and ρK Decays

Motivated by the large difference between the direct CP asymmetries $A_{CP}(B^-\to π^0 K^-)$ and $A_{CP}(\bar{B}^{0}\to π^{+} K^{-})$, we combine the up-to-date experimental information on $B\toπK$, $πK^{\ast}$ and $ρK$ decays to pursue possible solutions with the nonuniversal $Z^{\prime}$ model. Detailed analyses of the relative impacts of different types of couplings are presented in four specific cases. Numerically, we find that the new coupling parameters, $ξ^{LL}$ and $ξ^{LR}$ with a common nontrivial new weak phase $ϕ_L\sim-86^{\circ}$, which are relevant to the $Z^{\prime}$ contributions to the electroweak penguin sector $\triangle C_9$ and $\triangle C_7$, are crucial to the observed "$πK$ puzzle". Furthermore, they are found to be definitely unequal and opposite in sign. We also find that $A_{CP}(B^-\to ρ^0 K^-)$ can put a strong constraint on the new $Z^{\prime}$ couplings, which implies the $Z^{\prime}$ contributions to the coefficient of QCD penguins operator $O_3$ involving the parameter $ζ^{LL}$ required.

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arXiv2009

Studying Double Charm Decays of B_{u,d} and B_{s} Mesons in the MSSM with R-parity Violation

Motivated by the possible large direct CP asymmetry of \bar{B}^0_d \to D^+ D^- decay measured by Belle collaboration, we investigate double charm B_{u,d} and B_s decays in the minimal supersymmetric standard model with R-parity violation. We derive the bounds on relevant R-parity violating couplings from the current experimental data, which show quite consistent measurements among relative collaborations. Using the constrained parameter spaces, we explore R-parity violating effects on other observables in these decays, which have not been measured or have not been well measured yet. We find that the R-parity violating effects on the mixing-induced CP asymmetries of \bar{B}^0_d \to D^{(*)+} D^{(*)-} and \bar{B}^0_s \to D^{(*)+}_s D^{(*)-}_s decays could be very large, nevertheless the R-parity violating effects on the direct CP asymmetries could not be large enough to explain the large direct CP violation of \bar{B}^0_d \to D^{+} D^{-} from Belle. Our results could be used to probe R-parity violating effects and will correlate with searches for direct R-parity violating signals in future experiments.

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arXiv2008

Revisiting B\toπK, πK^{\ast} and ρK decays: CP violations and implication for New Physics

Combining the up-to-date experimental information on $B\toπK, πK^{\ast}$ and $ρK$ decays, we revisit the decay rates and CP asymmetries of these decays within the framework of QCD factorization. Using an infrared finite gluon propagator of Cornwall prescription, we find that the time-like annihilation amplitude could contribute a large strong phase, while the space-like hard spectator scattering amplitude is real. Numerically, we find that all the branching ratios and most of the direct CP violations, except $A_{CP}(B^{\pm}\to K^{\pm}π^{0})$, agree with the current experimental data with an effective gluon mass $m_g\simeq0.5 {\rm GeV}$. Taking the unmatched difference in direct CP violations between $B\toπ^{0} K^{\pm}$ and $π^{\mp}K^{\pm}$ decays as a hint of new physics, we perform a model-independent analysis of new physics contributions with a set of $\bar{s}(1+γ_{5})b\otimes\bar{q}(1+γ_{5})q$ (q=u,d) operators. Detail analyses of the relative impacts of the operators are presented in five cases. Fitting the twelve decay modes, parameter spaces are found generally with nontrivial weak phases. Our results may indicate that both strong phase from annihilation amplitude and new weak phase from new physics are needed to resolve the $πK$ puzzle. To further test the new physics hypothesis, the mixing-induced CP violations in $B\toπ^{0}K_{S}$ and $ρ^{0}K_{S}$ are discussed and good agreements with the recent experimental data are found.

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arXiv2007

QCD Approach to B->D πDecays and CP Violation

The branching ratios and CP violations of the $B\to Dπ$ decays, including both the color-allowed and the color-suppressed modes, are investigated in detail within QCD framework by considering all diagrams which lead to three effective currents of two quarks. An intrinsic mass scale as a dynamical gluon mass is introduced to treat the infrared divergence caused by the soft collinear approximation in the endpoint regions, and the Cutkosky rule is adopted to deal with a physical-region singularity of the on mass-shell quark propagators. When the dynamical gluon mass $μ_g$ is regarded as a universal scale, it is extracted to be around $μ_g = 440$ MeV from one of the well-measured $B\to Dπ$ decay modes. The resulting predictions for all branching ratios are in agreement with the current experimental measurements. As these decays have no penguin contributions, there are no direct $CP$ asymmetries. Due to interference between the Cabibbo-suppressed and the Cabibbo-favored amplitudes, mixing-induced CP violations are predicted in the $B\to D^{\pm}π^{\mp}$ decays to be consistent with the experimental data at 1-$σ$ level. More precise measurements will be helpful to extract weak angle $2β+γ$.

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arXiv2007

The rare decays $B^+_u\toπ^+\ell^+\ell^-$, $ρ^+\ell^+\ell^-$ and $B^0_d\to \ell^+\ell^-$ in the R-parity violating supersymmetry

We study the rare decays $B^{+}_u\to π^{+}\ell^{+}\ell^{-}$, $ρ^{+}\ell^{+}\ell^{-}$ and $B^{0}_d \to \ell^{+} \ell^{-}(\ell=e,μ)$ in the R-parity violating supersymmetric standard model. From the latest upper limits of $\mathcal{B}(B^+_u\toπ^+\ell^+\ell^-)$ and $\mathcal{B}(B^0_d\to\ell^+\ell^-)$, we have derived new upper bounds on the relevant R-parity violating couplings products, which are stronger than the existing ones. Using the constrained parameter space, we present the R-parity violating effects on the branching ratios and the forward-backward asymmetries of these decays. We find that $\mathcal{B}(B^0_d\to \ell^+\ell^-)$ and $\mathcal{B}(B^+_u \toρ^+\ell^+\ell^-)$ could be enhanced several orders by the R-parity violating sneutrino and squark exchanges, respectively. The R-parity violating effects on the dilepton invariant mass spectra of $B^+_u\to π^+\ell^+\ell^-$, $ρ^+\ell^+\ell^-$ and the normalized forward-backward asymmetry $\mathcal{A}_{FB}(B^+_u\toπ^+\ell^+\ell^-)$ and $\mathcal{A}_{FB}(B^+_u \toρ^+\ell^+\ell^-)$ are studied in detail. Our results could be used to probe the R-parity violating effects and will correlate with searches for the direct R-parity violating signals at the future experiments.

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arXiv2007

Constraints on the anomalous tensor operators from B\toϕK^{\ast}, ηK^{\ast}$ and ηK decays

We investigate whether the anomalous tensor operators with the Lorentz structure $σ_{μν} (1+γ_{5})\otimes σ^{μν}(1+γ_{5})$, which could provide a simple resolution to the polarization anomaly observed in $B\to ϕK^{\ast}$ decays, could also provide a coherent resolution to the large ${\cal B}(B\to ηK^{\ast})$ and survive bounds from $B\toηK$ decays. Parameter spaces satisfying all these experimental data are obtained, and found to be dominated by the color-octet tensor operator contribution. Constraints for the equivalent solution with $(1+γ_{5})\otimes(1+γ_{5})$ operators are also derived and found to be dominated by the color-singlet one. With the constrained parameter spaces, we finally give predictions for $B_{s}\to ϕϕ$ decay, which could be tested at the Fermilab Tevatron and the LHC-b experiments.

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arXiv2006

Probe the R-parity Violating Supersymmetry Effects in the $B^0_s-\bar{B}^0_s$ Mixing

The recent measurements of the $B_s$ mass difference $ΔM_s$ by the CDF and DØ collaborations are roughly consistent with the Standard Model predictions, therefore, these measurements will afford an opportunity to constrain new physics scenarios beyond the Standard Model. We consider the impact of the R-parity violating supersymmetry in the $B^0_s-\bar{B}^0_s$ mixing, and use the latest experimental results of $ΔM_s$ to constrain the size of the R-parity violating tree level couplings in the $B^0_s-\bar{B}^0_s$ mixing. Then, using the constrained R-parity violating parameter space from $ΔM_s$, we show the R-parity violating effects on the $B_s$ width difference $ΔΓ_{s}$.

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arXiv2006

Probe R-parity Violating Supersymmetry Effects in $B\to K^{(*)}\ell^+\ell^-$ and $B_s\to \ell^+\ell^-$ Decays

We study the decays $B\to K^{(*)}\ell^+\ell^-$ and $B_s\to \ell^+\ell^- (\ell=e,μ)$ in the minimal supersymmetric standard model with R-parity violation (RPV). From the recent measurements of their branching ratios, we have derived new upper bounds on the relevant RPV coupling products, which are stronger than the existing ones. Using the constrained parameter space, we predict the RPV effects on the forward-backward asymmetries ${\mathcal A}_{FB}(B\to K^{(*)}\ell^+\ell^-)$ and the branching ratios $ {\mathcal B}(B_s\to \ell^{+}\ell^{-}) $. Our results of the forward-backward asymmetries agree with the recent experiment data. It is also found that $\mathcal{B}(B_s\to \ell^+\ell^-)$ could be enhanced several orders by the RPV sneutrino exchange. The RPV effects on the dilepton invariant mass spectra of $B\to K^{(*)}\ell^+\ell^-$ and the normalized ${\mathcal A}_{FB}(B\to K^{(*)}\ell^+\ell^-)$ are studied in detail. Our results could be used to probe RPV effects and will correlate with searches for direct RPV signals at LHC.

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arXiv2006

Large Strong Phases and CP Violation in the Annihilation Processes $\bar{B}^0\to K^+K^-$, $K^{\pm}K^\mp$, $K^{+}K^{*-}$

The strong phases and CP violation in the rare $\bar{B}^0\to K^+K^-$, $K^{*\pm}K^\mp$, $K^{*+}K^{*-}$ decays are investigated. As these decays proceed only via annihilation type diagrams in the standard model (SM), a dynamical gluon mass is introduced to avoid the infrared divergence in the soft endpoint regions. The Cutkosky rule is adopted to deal with a physical-region singularity of the on mass-shell quark propagators, which leads to a big imaginary part and hence a large strong phase. As a consequence, large CP asymmetries are predicted in those decay modes due to a big interference between the annihilation amplitudes from penguin and tree operators, which may be tested in future more precise experiments.

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arXiv2006

The rare decays B --> K() anti-K() and R-parity violating supersymmetry

We study the branching ratios, the direct CP asymmetries in $B\to K^{(*)}\bar{K}^{(*)}$ decays and the polarization fractions of $B\to K^{*}\bar{K}^{*}$ decays by employing the QCD factorization in the minimal supersymmetric standard model with R-parity violation. We derive the new upper bounds on the relevant R-parity violating couplings from the latest experimental data of $B\to K^{(*)}\bar{K}^{(*)}$, and some of these constraints are stronger than the existing bounds. Using the constrained parameter spaces, we predict the R-parity violating effects on the other quantities in $B\to K^{(*)}\bar{K}^{(*)}$ decays which have not been measured yet. We find that the R-parity violating effects on the branching ratios and the direct $CP$ asymmetries could be large, nevertheless their effects on the longitudinal polarizations of $B\to K^{*}\bar{K}^{*}$ decays are small. Near future experiments can test these predictions and shrink the parameter spaces.

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arXiv2006

MSSM Anatomy of the Polarization Puzzle in B --> phi K* Decays

We analyze the $B \to ϕK^{*}$ polarization puzzle in the Minimal Supersymmetric Standard Model (MSSM) including the neutral Higgs boson (NHB) contributions. To calculate the non-factorizable contributions to hadronic matrix elements of operators, we have used the QCD factorization framework to the $α_s $ order. It is shown that the recent experimental results of the polarization fractions in $B\to ϕK^{*}$ decays, which are difficult to be explained in SM, could be explained in MSSM if there are flavor non-diagonal squark mass matrix elements of 2nd and 3rd generations, which also satisfy all relevant constraints from known experiments ($B\to X_sγ, B_s\to μ^+μ^-, B\to X_s μ^+μ^-, B\to X_s g, ΔM_s$, etc.). We have shown in details that the experimental results can be accommodated with the flavor non-diagonal mass insertion of chirality RL, RL+LR, RR, or LL+ RR when the NHB contributions as well as $\mathcal{O}(α_s)$ corrections of hadronic matrix elements of operators are included. However the branching ratios for the decay are smaller than the experimental measurements.

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arXiv2005

The puzzles in $B\to ππ$ and $ πK$ decays: possible implications for R-parity violating supersymmetry

Recent experiments suggest that certain data of $B \to ππ,πK$ decays are inconsistent with the standard model expectations. We try to explain the discrepancies with R-parity violating suppersymmetry. By employing the QCD factorization approach, we study these decays in the minimal supersymmetric standard model with R-parity violation. We show that R-parity violation can resolve the discrepancies in both $B \to ππ$ and $B \to πK$ decays, and find that in some regions of parameter spaces all these requirements, including the CP averaged branching ratios and the direct CP asymmetries, can be satisfied. Furthermore, we have derived stringent bounds on relevant R-parity violating couplings from the latest experimental data, and some of these constraints are stronger than the existing bounds.

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arXiv2005

Reexamining $ B\to ππ,πK$ Decays in QCD Factorization Approach

Motivated by the recent experimental data, we have revisited the $B\to πK,ππ$ decays in the framework of QCD factorization, with inclusion of the important strong penguin corrections of order $α_s^2$ induced by $b\to D g^\ast g^\ast$ ($D=d$ or $s$ and $g^\ast$ denotes an off-shell gluon) transitions. We find that these higher order strong penguin contributions can provide $\sim 30%$ enhancement to the penguin-dominated $B\to πK$ decay rates, and such an enhancement can improve the consistency between the theoretical predictions and the experimental data significantly, while for the tree-dominated $B\to ππ$ decays, these higher order contributions play only a minor role. When these strong penguin contributions are summed, only a small strong phase remains and the direct CP asymmetries get small corrections. We also find patterns of the ratios between the CP-averaged branching fractions remain nearly unaffected even after including these higher order corrections and the $πK$ puzzle still persists. Our results may indicate that to resolve the puzzle one would have to resort to new physics contributions in the electroweak penguin sector as found by Buras {\it et al}.

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arXiv2005

Revisiting the annihilation decay $\bar{B}_{s}\toπ^{+}π^{-}$

It is very important to know the strength of annihilation contribution in B charmless nonleptonic decays. $\bar{B}_{s}\to π^{+}π^{-}$ process could serve a good probe of the strength. We have studied the process in QCD factorization framework. Using a gluon mass scale indicted by the studies of infrared behavior of gluon propagators to avoid enhancements in the soft end point regions, we find that the CP averaged branching ratio is about $1.24\times 10^{-7}$, the direct CP asymmetry $C_{ππ}$ is about -0.05, while the mixing-induced CP asymmetry quite large with the value $S_{ππ}$=0.18. The process could be measured at LHC-b experiments in the near future and would deepen our understanding of dynamics of B charmless decays.

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