arXiv subjects

Zhenjun Xiao

Publications and source records attributed to Zhenjun Xiao.

36 records · Page 2Linked to original sources

arXiv2001

Branching ratios and CP-violating asymmetries of $B_s \to h_1 h_2 $ decays in the general two-Higgs doublet models

Based on the low-energy effective Hamiltonian with the generalized factorization, we calculate the new physics contributions to branching ratios and CP-violating asymmetries of the charmless hadronic decays $B_s \to h_1 h_2$ in the standard model and the general two-Higgs doublet models (models I, II, and III). Within the considered paramter space, we find the following. (a) In models I and II, the new physics corrections are always small in size and will be masked by other larger known theoretical uncertainties. (b) In model III, the new physics corrections to the branching ratios of those QCD penguin-dominated decays $\ov B_s \to K^0\etapp, K^+ K^{-*}, etc.$, are large in size and insensitive to the variations of $\mhp$ and $\nceff$. For tree- or electroweak penguin-dominated decay modes, however, the new physics corrections are very small in size. (c) For $\ov B_s \to K^+ K^{-*}$ and other seven decay modes, the branching ratios are at the level of $(1-3)\times 10^{-5}$ and will be measurable at the future hadron colliders with large $b$ production. (d) Among the studied thirty nine $B_s$ meson decay modes, seven of them can have a CP-violating asymmetry ${\cal A}_{CP}$ larger than 20% in magnitude. The new physics corrections are small or moderate in magnitude. (e) Because of its large and $\nceff$ stable branching ratio and CP violating asymmetry, the decay $\ov B_s \to K^+ K^{-*}$ seems to be the "best" channel to find CP violation of $B_s$ system through studies of two-body charmless decays of $B_s$ meson.

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arXiv2001

The $B -> X_s gamma gamma$ decay in the standard model and the general two-Higgs-doublet model

Based on the low-energy effective Hamiltonian, we calculate the new physics corrections to the branching ratio and the differential distributions of the rare decay $B \to X_s γγ$ induced by the new gluonic and electroweak charged-Higgs penguin diagrams in the general two-Higgs-doublet model with the restriction $λ_{ij}^{U,D}=0$ for $i\neq j$. Within the considered parameter space, we see the following: (a) the standard model predictions of ${\cal B}(B \to X_s γγ)$ and $A_{FB}$ have a moderate $m_s$ dependence; (b) in model III, the prediction of the branching ratio ${\cal B}(B \to X_s γγ)$ ranges from one third to three times of the standard model prediction, but is highly correlated with that of ${\cal}(B \to X_s γ)$; (c) the new physics enhancement to the branching ratio ${\cal B}(B \to X_s γγ)$ in model II can be as large as $(30-50)%$; (d) the contribution from 1PR diagrams is dominant and hence four normalized differential distributions are insensitive to the variation of scale $μ$ and possible new physics corrections; (e) due to the smallness of its decay rate and the long-distance background, the $B \to X_s γγ$ decay is not a better process in detecting new physics than the $B \to X_s γ$ decay.

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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.

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arXiv2000

Charmless hadronic decays $B \to PP, PV, VV$ and new physics effects in the general two-Higgs doublet models

Based on the low-energy effective Hamiltonian with the generalized factorization, we calculate the new physics contributions to the branching ratios of the two-body charmless hadronic decays of $B_u$ and $B_d$ mesons induced by the new gluonic and electroweak charged-Higgs penguin diagrams in the general two-Higgs doublet models (models I, II and III). Within the considered parameter space, we find that: (a) the new physics effects from new gluonic penguin diagrams strongly dominate over those from the new $γ$- and $Z^0$- penguin diagrams; (b) in models I and II, new physics contributions to most studied B meson decay channels are rather small in size: from -15% to 20%; (c) in model III, however, the new physics enhancements to the penguin-dominated decay modes can be significant, $\sim (30 -200)%$, and therefore are measurable in forthcoming high precision B experiments; (d) the new physics enhancements to ratios ${\cal B}(B \to K \etap)$ are significant in model III, $\sim (35 -70)%$, and hence provide a simple and plausible new physics interpretation for the observed unexpectedly large $B \to K \etap $ decay rates; (e) the theoretical predictions for ${\cal B}(B \to K^+ π)$ and ${\cal B}(B \to K^0 π^+)$ in model III are still consistent with the data within $2σ$ errors; (f) the significant new physics enhancements to the branching ratios of $B \to K^0 π^0, K^* η, K^{*+} π^-, K^+ ϕ, K^{*0} ω, K^{*+} ϕ$ and $K^{*0} ϕ$ decays are helpful to improve the agreement between the data and the theoretical predictions; (g) the theoretical predictions of ${\cal B}(B \to PP, PV, VV)$ in the 2HDM's are generally consistent with experimental measurements and upper limits ($90% C.L.$)

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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.

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arXiv2000

Charm multiplicity and the branching ratios of inclusive charmless b quark decays in the general two-Higgs-doublet models

In the framework of general two-Higgs-doublet models, we calculate the branching ratios of various inclusive charmless b decays by using the low energy effective Hamiltonian including next-to-leading order QCD corrections, and examine the current status and the new physics effects on the determination of the charm multiplicity $n_c$ and semileptonic branching ratio $B_{SL}$. Within the considered parameter space, the enhancement to the ratio $BR(b \to s g)$ due to the charged-Higgs penguins can be as large as a factor of 8 (3) in the model III (II), while the ratio $BR(b \to no charm)$ can be increased from the standard model prediction of 2.49% to 4.91% (2.99%) in the model III (II). Consequently, the value of $B_{SL}$ and $n_c$ can be decreased simultaneously in the model III. The central value of $B_{SL}$ will be lowered slightly by about 0.003, but the ratio $n_c$ can be reduced significantly from the theoretical prediction of $n_c= 1.28 \pm 0.05$ in the SM to $n_c= 1.23 \pm 0.05$, $1.18 \pm 0.05$ for $m_{H^+}=200, 100$ GeV, respectively. We find that the predicted $n_c$ and the measured $n_c$ now agree within roughly one standard deviation after taking into account the effects of gluonic charged Higgs penguins in the model III with a relatively light charged Higgs boson.

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arXiv1999

Gluon penguin enhancements to inclusive charmless decays of b quark in the 2HDM with flavor changing couplings

We calculate the enhancements to the inclusive charmless decays of b quark, $b \to s g, s q\bar{q}, sgg$, from gluon penguin diagrams induced by the charged and neutral Higgs bosons $(H^{\pm}, h^0, H^0$, and A^0) in the Two-Higgs-Doublet Model with flavor-changing couplings. Within the considered parameter space, the new contributions from charged Higgs boson are dominant. After including the new contributions, the branching ratio $BR(b \to sg)$ (q^2 =0) can be increased form $\sim 0.2%$ in the standard model to 4.4% and 2.6% in the two-Higgs-doublet model for $m_{H^+}=100$ and 200 GeV, respectively. The new contribution to the decay mode $b \to s q \bar{q}$ with q=(u,d,s) is, however, numerically small and peaked at the lower q^2 region. The new contribution to $b \to s gg$ can also be neglected.

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arXiv1999

Inclusive $η'$ production in B decays and the Enhancement due to charged technipions

The new contributions to the charmless B decay $B \to X_{s}η^{\prime}$ from the unit-charged technipions $P^{\pm}$ and $P^{\pm}_{8}$ are estimated. The technipions can provide a large enhancement to the inclusive branching ratio: $Br(B \to X_{s}η^{\prime}) \sim 7\times 10^{-4}$ for $m_{p1}=100GeV$ and $m_{p8}=250 \sim 350 GeV$ when the effect of QCD gluon anomaly is also taken into account. The new physics effect is essential to interpret the CLEO data.

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arXiv1999

The rare K-decays in the Multiscale Walking Technicolor Model

We calculate the one-loop $Z^0$-penguin contributions to the rare K-decays, $K^+ \to π^+ ν\bar ν$, $K_L \to π^0 ν\bar ν$ and $K_L \to μ^+ μ^-$, from the unit-charged technipions $π_1$ and $π_8$ in the framework of the Multiscale Walking Technicolor Model. We find that: (a) the $π_1$ and $π_8$ can provide one to two orders enhancements to the branching ratios of the rare K-decays; (b) by comparing the experimental data of $Br(K^+ \to π^+ ν\bar ν)$ with the theoretical prediction one finds the lower mass bounds, $m_{p8} \geq 249 GeV$ for $F_Q=40GeV$ and $m_{p1}=100 GeV$; (c) by comparing the experimental data of $Br(K_L \to μ^+ μ^-)$ with the theoretical predictions one finds the lower bounds on $m_{p1}$ and $m_{p8}$, $m_{p1} \geq 210 GeV$ if only the contribution from $π_1$ is taken into account, and $m_{p8} \geq 580 GeV$ for $m_{p1}=210 GeV$, assuming $F_Q=40GeV$; (d) the assumed ranges of the masses $m_{p1}$ and $m_{p8}$ in the Multiscale Walking Technicolor Model are excluded by the rare K-decay data.

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arXiv1999

The rare K-decays and $Z^0$-penguin contributions in the Topcolor-assisted technicolor models

We calculate the new contributions to the rare decays $K^+ \to π^+ ν\bar ν$, $K_L \to π^0 ν\bar ν$ and $K_L \to μ^+ μ^-$ from new $Z^0$-penguin and box diagrams induced by the unit-charged scalars $(\tildeπ^\pm, \tilde{H}^\pm, π_1^\pm, π_8^\pm)$ appeared in the Topcolor-assisted technicolor (TC2) models. We find that: (a) the unit-charged top-pion $\tildeπ^\pm$ and b-pion $\tilde{H}^\pm$ can provide large contributions to the rare K-decays if they are relatively light; (b) the size of mixing elements $D_{L,R}^{ij}$ ($i \neq j$) is strongly constrained by the data of $B^0$ meson mixing: $|a_R^{ts}|, |a_R^{td}| < 0.01$ for $a_L^{td}=a_L^{ts}=1/2$ and $m_{\tilde{H}^0}\leq 600GeV$; (c) the enhancements to the branching ratios of rare K-decays from new scalars can be as large as one order of magnitude; (d) there is a strong cancellation between the short- and long-distance dispersive part of the decay $K_L \to μ^+ μ^-$, the constraint on the new short-distance part from this decay mode is thus not strong; (e) the typical TC2 model under study is generally consistent with the available rare K-decay data.

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arXiv1997

Technicolor leptoquarks and the excess of NC and CC events with high-$Q^2$ at HERA

In this paper we pursue a consistent leptoquark interpretation for HERA anomalies in the framework of Technicolor. We find that: (a) one F=0 scalar Technicolor leptoquark $P_3^{'}$ with a mass of 200 GeV can provide the required contributions to account for the excess of both neutral and charged current events with high-$Q^2$ at HERA; (b) the current data still allow the coexistence of $ P_3^{'}$ with m(P_3^{'})= 200 GeV$ and $P_3^0$ with $m(P_3^0)=225 GeV$, they could contribute effectively to $e^+p$ collision process and may be responsible for the apparent splitting of average mass of H1 and ZEUS NC events with high-$Q^2$.

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arXiv1997

TC corrections to the single-top-quark production at the Fermilab Tevatron

We calculate one-loop corrections to the single-top-quark production via $q\overline{q}' \to t\overline b$ at the Fermilab Tevatron from the Pseudo-Goldstone bosons ( PGBs ) in the framework of one generation technicolor model. The maximum correction to the total cross section for the single-top-quark production is found to reach -2.4% relative to the tree-level cross section, which may be observable at a high-luminosity Tevatron.

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arXiv1996

Multiscale Technicolor and $b \to s γ$

Correction to the $b\rightarrow sγ$ branching ratio in the multiscale walking technicolor model (MWTCM) is examined. For the original MWTCM, the correction is too large to explain the recent CLEO data. We show that if topcolor is further introduced, the branching ratio in the topcolor assisted MWTCM can be in agreement with the CLEO data for a certain range of the parameters.

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arXiv1996

Precision Data and Implications on the Parameters of TC theory

Assuming that the actual values of $m_t$ and the data set ($Γ_b$, $Γ_h$, $Γ_Z$, $R_b$, $R_c$, $R_l$) are within their $1-σ$ errors as reported by CDF, D0 and by LEP Collaborations, the parameter $Δ^{new}_b$ which measures the nonoblique corrections on the $Zb\overline{b}$ vertex from new physics can be determined experimentally. According to the precision data one can obtain updated constraints on the parameters $ξ$ and the masses of the charged PGBs.

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arXiv1996

A study on the rare radiative decay $B_c \to D_s^*γ$ in technicolor with scalars

Applying the perturbative QCD (PQCD), we study the process $B_c\rightarrow D_s^*γ$ in the technicolor with a massless scalar doublet model (TCMLSM) recently presented by C. D. Carone and H. Georgi; and compare the results with that estimated in the standard model (SM). There are two mechanisms which contribute to the $B_c\rightarrow D_s^* γ$ process. One proceeds through the short distance $b\rightarrow s γ$ transition, the other through weak annihilation accompanied by a photon emission. In the SM, these two processes are found to contribute with the same order of magnitude. In the TCMLSM, the modification of $B_c\rightarrow D_s^*γ$ from $π_p$ (the physical pions in this model) is small for the allowed mass of $π_p$.

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arXiv1996

Study on the rare radiative decay $B_c \to D_s^*γ$ in the standard model and multiscale walking technicolor model

Applying the perturbative QCD ( PQCD ) method, we study the decay $B_c\rightarrow D_s^*γ$ in the standard model and multiscale walking technicolor model. In the SM, we find that the contribution of weak annihilation is more important than that of the electromagnetic penguin. The presence of Pseudo-Goldstone-Bosons in the MWTCM leads to a large enhancement in the rate of $B_c\rightarrow D_s^*γ$, but this model is in conflict with the branching ratio of $Z\rightarrow b\overline b$ ( $R_b$ ) and the CLEO data on the branching ratio BR ( $b\rightarrow sγ$ ). If topcolor is further introduced, the calculated results in the topcolor assisted MWTCM can be suppressed and be in agreement with the CLEO data for a certain range of the parameters.

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arXiv1995

Constraints on Masses of Charged PGBs in Technicolor Model from Decay $ b \to s γ$

In this paper we calculate the contributions to the branching ratio of $B\to X_s γ$ from the charged Pseudo-Goldstone bosons appeared in one generation Technicolor model. The current $CLEO$ experimental results can eliminate large part of the parameter space in the $m(P^\pm) - m(P_8^\pm)$ plane, and specifically, one can put a strong lower bound on the masses of color octet charged PGBs $P_8^\pm$: $m(P^{\pm}_8) > 400\;GeV$ at $90\%C.L$ for free $m(P^{\pm})$.

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arXiv1995

Pseudo-Goldstone Bosons in Technicolor Models and the Phenomenology

In this report we present a review of recent developments in the TC/ETC theories, concentrating on the theoretical estimations and the phenomenological analysis about the Non-Oblique corrections on the $Zb\overline{b}$ vertex from ETC dynamics and Pseudo-Goldstone Bosons. The relevant studies about the vertex corrections on other processes from the PGBs were also considered.

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