arXiv subjects

Libo Guo

Publications and source records attributed to Libo Guo.

9 recordsLinked to original sources

arXiv2006

$B \to K K^{*}$ Decays in the Perturbative QCD Approach

We calculate the branching ratios and CP-violating asymmetries for $B^0 \to K^{0} \ov K^{*0}$, $\ov K^{0} K^{*0}$, $K^+ K^{*-}$, $K^- K^{*+}$, and $B^+\to K^+ \ov K^{*0}$ and $ \ov K^0 K^{*+} $ decays by employing the low energy effective Hamiltonian and the perturbative QCD (pQCD) factorization approach. The theoretical predictions for the branching ratios are $Br(B^0/\ov B^0 \to K^{\pm} K^{*\mp}) \approx 7.4 \times 10^{-8}$, $Br(B^0/\ov B^0 \to K^{0} \ov K^{*0}(\ov K^{0} K^{*0})) \approx 19.6 \times 10^{-7}$, $Br(B^+\to K^+ \ov K^{*0}) \approx 3 \times 10^{-7}$ and $Br(B^+\to K^{*+} \ov K^0) \approx 18.3 \times 10^{-7}$, which are consistent with currently available experimental upper limits. We also predict large CP-violating asymmetries in these decays: $A_{CP}^{dir}(K^\pm \ov K^{*0})\approx -20 %$, $A_{CP}^{dir}(K^{*\pm} \ov K^0)\approx -49%$, which can be tested by the forthcoming B meson experiments.

hep-ph↗

arXiv2006

Branching Ratio and CP Asymmetry of $B \to ρη^{(\prime)}$ Decays in the Perturbative QCD Approach

In this paper,we calculate the branching ratios and CP-violating asymmetries for $B^0 \to ρ^0 η^{(\prime)}$ and $B^+\to ρ^+ \etap$ decays in the perturbative QCD factorization approach. In this approach, we not only calculate the usual factorizable contributions, but also evaluate the non-factorizable and annihilation type contributions. Besides the current-current operators, the contributions from the QCD and electroweak penguin operators are also taken into account. The theoretical predictions for the branching ratios are $Br(B^+ \to ρ^+ η^{(\prime)}) \approx 9 \times 10^{-6}$ and $Br(B^0 \to ρ^0 η^{(\prime)}) \approx 5 \times 10^{-8}$, which agree well with the measured values and currently available experimental upper limits. We also predict large CP-violating asymmetries in these decays: $A_{CP}^{dir}(ρ^\pm η)\approx -13 %$, $A_{CP}^{dir}(ρ^\pm η^\prime)\approx -18 %$, $A_{CP}^{dir}(ρ^0 η)\approx -41%$, $A_{CP}^{dir}(ρ^0 η^\prime)\approx -27%$, $A_{CP}^{mix}(ρ^0 η)\approx +25%$, and $A_{CP}^{mix}(ρ^0 η^\prime) \approx +11%$, which can be tested by the current or future B factory experiments.

hep-ph↗

arXiv2005

Branching Ratio and CP Asymmetry of $B \to πη^{(\prime)}$ Decays in the Perturbative QCD Approach

We calculate the branching ratios and CP-violating asymmetries for $B^0 \to π^0 η^{(\prime)}$ and $B^+\to π^+ η^{(\prime)}$ decays in the perturbative QCD (pQCD) factorization approach here. We not only calculate the usual factorizable contributions, but also evaluate the non-factorizable and annihilation type contributions. Besides the current-current operators, the contributions from the QCD and electroweak penguin operators are also taken into account. The pQCD results for the CP-averaged branching ratios are $Br(B^+ \to π^+ η) \approx 4.1 \times 10^{-6}$, $Br(B^+ \to π^+ η^\prime) \approx 2.4 \times 10^{-6}$, and $Br(B^0 \to π^0 η^{(\prime)}) \approx 0.2 \times 10^{-6}$, which agree very well with the measured values or currently available experimental upper limits. We also predict large CP-violating asymmetries in these decays: $A_{CP}^{dir}(π^\pm \etap)\sim A_{CP}^{dir}(π^0 \etap)\sim -0.35 $, and $A_{CP}^{mix}(π^0 \etap)\sim 0.67$, but with large errors. The pQCD prediction for $A_{CP}^{dir}(π^\pm η)$ ($A_{CP}^{dir}(π^\pm η^\prime))$ has the same (opposite) sign with the primary measured values. Further improvements in both theory and experiments are needed to clarify this discrepancy.

hep-ph↗

arXiv2003

B^0-\bar{B}^0 mixing and B \to X_s γdecay in the third type 2HDM: effects of NLO QCD contributions

In this paper, we calculated the next-to-leading order (NLO) new physics contributions to the mass splitting $\dmd$ and the branching ratio $\brbxsga$ induced by the charged Higgs loop diagrams in the third type of two-Higgs-doublet models (model III) and draw the constraints on the free parameters of model III. For the model III under consideration, we found that (a) an upper limit $|\ltt|\leq 1.7$ is obtained from the precision data of $\dmd=0.502 \pm 0.007 ps^{-1}$, while $|\ltt| \approx 0.5$ is favored phenomenologicaly; (b) for $B \to X_s γ$ decay, the NLO QCD contributions tend to cancel the LO new physics contributions; (c) a light charged Higgs boson with a mass around or even less than 200 GeV is still allowed at NLO level by the measured branching ratio $\brbxsga$: numerically, $188 \leq \mh \leq 215$ GeV for $(|\ltt|,|\lbb|)=(0.5,18)$; (d) the NLO QCD contributions tend to cancel the LO contributions effectively, the lower limit on $\mh$ is consequently decreased by about 200 GeV; (e) the allowed region of $\mh$ will be shifted toward heavy mass end for a non-zero relative phase $θ$ between the Yukawa couplings $\ltt$ and $\lbb$. The numerical results for the conventional model II are also presented for the sake of a comparison.

hep-ph↗

arXiv2003

Charmless hadronic decays $B \to VV$ in the Topcolor-assisted Technicolor model

Based on the effective Hamiltonian with the generalized factorization approach, we calculate the branching ratios and CP asymmetries of $B \to VV$ decays in the Topcolor-assisted Technicolor (TC2) model. Within the considered parameter space we find that: (a) for the penguin-dominated $B \to K^{*+}ϕ$ and $K^{*0}ϕ$ decays, the new physics enhancements to the branching ratios are around 40%; (b) the measured branching ratios of $B \to K^{*+} ϕ$ and $ K^{*0} ϕ$ decays prefer the range of $3 \lesssim \nceff \lesssim 5$; (c) the SM and TC2 model predictions for the branching ratio ${\cal B}(B^+ \to ρ^+ ρ^0)$ are only about half of the Belle's measurement; and (d) for most $B \to VV$ decays, the new physics corrections on their CP asymmetries are generally small or moderate in magnitude and insensitive to the variation of $\mpcc$ and $\nceff$.

hep-ph↗

arXiv2003

Constraints on the CKM angle $α$ from the measured CP asymmetries and branching ratios of $B \to π^+ π^-, π^+ π^0$ and $K^0π^+$ decays

In this paper, we draw constraints on the Cabibbo-Kobayashi-Maskawa (CKM) angle $α$ and the strong phase $δ$ from the experimental measurements of $\ssb$, the CP-violating asymmetries and branching ratios of $B \to π^+ π^-, π^+ π^0$ and $K^0 π^+$ decays. In the SM, the measured $\ssb$ leads to an upper limit on $α$: $α\leq 180^\circ-β$. Taking the weighted-average of the newest BaBar and Belle measurements of $\spp$ and $\app$ in $B^0 \to π^+π^-$ decay as the experimental input, we find the allowed range of angle $α$, $76^\circ \leq α\leq 135^\circ$ for $r=|P/T| =0.3 \pm 0.1 $. From the measured CP-averaged branching ratios of $B \to π^+ π^-, π^+ π^0$ and $K^0 π^+$ decays, we found an inequality, $\cosα \cosδ \geq 0.45$. The region of $70^\circ \leq α\leq 110^\circ$ is thus excluded by applying this inequality. The combined constraints on $α$ and $δ$ are $117^\circ \leq α\leq 135^\circ$ and $-160^\circ \leq δ\leq -132^\circ$ if we take $\spp=0.49 \pm 0.27$ and $\app=0.51 \pm 0.19$ as the experimental input. The new lower limit on the angle $α$ is dominated by the measured branching ratios considered in this paper, and is much stronger than those obtained before.

hep-ph↗

arXiv2001

$\etap K$ puzzle of B meson decays and new physics effects in the TC2 model

Using the low energy effective Hamiltonian with the generalized factorization, we calculate the new physics contributions to $B \to π^+ π^-, K π$ and $K \etap$ in the Topcolor-assisted-Technicolor(TC2) model, and compare the results with the available data. By using $F_0^{\rm Bπ}(0)=0.20\pm 0.04$ preferred by the CLEO data of $B \to π^+ π^-$ decay, we find that the new physics enhancements to $B \to K \etap$ decays are significant in size, $\sim 50%$ with respect to the standard model predictions, insensitive to the variations of input parameters and hence provide a simple and plausible new physics interpretation for the observed unexpectedly large $B\to K \etap$ decay rates.

hep-ph↗

arXiv2000

Charmless decays B -> PP, PV, and effects of new strong and electroweak penguins in Topcolor-assisted Technicolor model

Based on the low energy effective Hamiltonian with generalized factorization, we calculate the new physics contributions to the branching ratios and CP-violating asymmetries of the two-body charmless hadronic decays $B \to PP, PV$ from the new strong and electroweak penguin diagrams in the TC2 model. The top-pion penguins dominate the new physics corrections, and both new gluonic and electroweak penguins contribute effectively to most decay modes. For tree-dominated decay modes $B \to ππ, ρπ, etc,$ the new physics corrections are less than 10%. For decays $B \to K^{(*)} π$, $K^{(*)} η$, $etc$, the new physics enhancements can be rather large (from $- 70%$ to $\sim 200%$) and are insensitive to the variations of $N_c^{eff}$, $k^2$, $η$ and $m_{\tildeπ}$ within the reasonable ranges. For decays $B^0 \to ϕπ$, $ϕη^{(')}$, $K^* \bar{K}^0$ and $ρ^+ K^0$, $δ{\cal B}$ is strongly $N_c^{eff}-$dependent: varying from -90% to $\sim 1680%$ in the range of $N_c^{eff}=2-\infty$. The new physics corrections to the CP-violating asymmetries ${\cal A}_{CP}$ vary greatly for different B decay channels. For five measured CP asymmetries of $B \to K π, K η', ωπ$ decays, $δ{\cal A}_{CP}$ is only about 20% and will be masked by large theoretical uncertainties. The new physics enhancements to interesting $B \to K η'$ decays are significant in size ($\sim 50%$), insensitive to the variations of input parameters and hence lead to a plausible interpretation for the unexpectedly large $B \to K η'$ decay rates. The TC2 model predictions for branching ratios and CP-violating asymmteries of all fifty seven $B \to PP, PV$ decay modes are consistent with the available data within one or two standard deviations.

hep-ph↗

arXiv1995

Electroweak Penguin Contributions in $B^-(\overline {B_d^0}) \to PP$ and $PV$ decays Beyond Leading Logarithms

Using the next-to-leading order low energy effective Hamiltonian for $|ΔB|=1$, $ΔC=ΔU=0$ transitions, the contributions of electroweak penguin operators in $ B^-(\overline {B_d^0})\rightarrow PP$ and $PV$ decays are estimated in the standard model. We find that, for some channels, the electroweak penguin effects can enhance or reduce the QCD penguin and/or tree level contributions by at least $30\%$, and can even play dominant role.

hep-ph↗