arXiv subjects
Publications and source records attributed to Zhen-jun Xiao.
In this short review we elaborate the significance of resummation in $k_T$ factorization theorem, and summarize the recent progresses in the calculations of the next-to-leading order contributions to B meson decays from the perturbative QCD (PQCD) approach. We also comment on the current status of the PQCD approach and highlight some key issues to develop it in the near future for more phenomenological applications.
We revisit the proof of the perturbative QCD factorization for the exclusive processes $ργ^{\star} \to π(ρ)$ at the two-parton twist-3 level. It is pointed out that the residual collinear divergences observed in the literature, which break the factorization of the above processes at the considered accuracy, are attributed to the improper insertion of the Fierz identity for factorizing the fermion flow. We show that the factorization theorem indeed holds at the two-parton twist-3 level after the mishandling is corrected.
In this paper we firstly demonstrate step by step that the factorization hypothesis is valid at the next-to-leading order (NLO) for the exclusive process $ργ^{\star} \to ρ$ by employing the collinear factorization approach, and then extend this proof to the case of the $k_T$ factorization by taking into account the transversal momentum of the light external quark (anti-quark) lines in the $ρ$ meson. At the NLO level, we then show that the soft divergences from different sub-diagrams will be canceled each other in the quark level, while the remaining collinear divergences can be absorbed into the NLO meson wave functions. The full NLO amplitudes can therefore be factorized as the convolution of the NLO wave functions $ Φ^{(1)}_ρ$ and the infrared-finite leading order (LO) hard kernels $G^0_{X,IJ,kl}$ in the $k_T$ factorization. We also write down the polarized NLO $ρ$ meson wave functions in the form of nonlocal hadron matrix elements with the gauge factor integral path deviating from the light cone. These NLO $ρ$ meson wave functions can be used to calculate the NLO hard corrections to some relevant exclusive processes, such as $B \to ρ$ transition.
The lighter chargino three body decays $\tildeχ_1^\pm\to \tildeχ_1^0 f f^\prime$ via the $W^\pm$ boson and the charged Higgs boson $H^\pm$ are studied in the R-parity conserved Minimal Supersymmetric Standard Model (MSSM). We treat $\tilde χ_1^\pm$ decays as production and decay of $W^\pm$ and $H^\pm$: i.e., $\tildeχ_1^\pm \to \tildeχ_1^0 W^\pm (H^\pm) \to \tildeχ_1^0 f f^\prime$. Both higgsino-like and wino-like $\tilde χ_1^\pm$ decays are well investigated. These decays are calculated at 1-loop level and the loop corrections are found to be less than three percent.The signal of the charged Higgs $H^\pm$ production from $\tilde χ_1^\pm$ decays are discussed. It will offer important information about the chargino and neutralino sector, as well as the charged Higgs sector in the MSSM.
In this article, we calculate the branching ratios of $B \to K_0^*(1430) K$ decays by employing the perturbative QCD (pQCD) approach at leading order. We perform the evaluations in the two scenarios for the scalar meson spectrum. We find that (a) the leading order pQCD predictions for the branching ratio $Br(B^+ \to K^+ \bar{K_0^*}(1430)^0)$ which is in good agreement with the experimental upper limit in both scenarios, while the pQCD predictions for other considered $B \to K_0^*(1430) K$ decay modes are also presented and will be tested by the LHC experiments; (b) the annihilation contributions play an important role in these considered decays, for $B^0 \to {K_0^*}(1430)^\pm {K}^\mp$ decays, for example, which are found to be $(1-4) \times 10^{-6}$.
In the topcolor-assistant technicolor (TC2) model, the typical physical particles, top-pions and top-Higgs, are predicted and the existence of these particles could be regarded as the robust evidence of the model. These particles are accessible at the Tevatron and LHC, and furthermore the flavor-changing(FC) feature of the TC2 model can provide us a unique chance to probe them. In this paper, we study some interesting FC production processes of top-pions and top-Higgs at the Tevatron and LHC, i.e., $cΠ_{t}^{-}$ and $cΠ_{t}^{0}(h_{t}^{0})$ productions. We find that the light charged top-pions are not favorable by the Tevatron experiments and the Tevatron has a little capability to probe neutral top-pion and top-Higgs via these FC production processes. At the LHC, however, the cross section can reach the level of $10\sim 100$ pb for $cΠ_t^-$ production and $ 10\sim 100$ fb for $cΠ_t^0(h_t^0)$ production. So one can expect that enough signals could be produced at the LHC experiments. Furthermore, the SM background should be clean due to the FC feature of the processes and the FC decay modes $Π_t^-\to b\bar{c}, Π_t^0(h_t^0)\to t\bar{c}$ can provide us the typical signal to detect the top-pions and top-Higgs. Therefore, it is hopeful to find the signal of top-pions and top-Higgs with the running of the LHC via these FC processes.
In this paper, we calculate the branching ratios and CP-violating asymmetries for $B_{s} \to (ρ^0,ω, ϕ) η^{(\prime)}$ decays in the perturbative QCD (pQCD) factorization approach. Numerically we found that (a) the pQCD predictions for the CP-averaged branching ratios are $Br(B_{s}\toρ^0 η)\approx 0.07 \times 10^{-6}$, $Br(B_{s}\toρ^{0}η^\prime) \approx 0.10 \times 10^{-6}$, $Br(B_{s} \toωη) \approx 0.02 \times 10^{-6}$, $Br(B_{s} \toωη^\prime) \approx 0.13 \times 10^{-6}$, $Br(B_{s} \toϕη) \approx 2.7 \times 10^{-5}$ and $Br(B_{s} \toϕη^\prime) \approx 2.0 \times 10^{-5}$; (b) the gluonic contributions are small in size: less than 3% for $B \to (ρ, ω, ϕ) η$ decays, and about 10% for $B \to (ρ, ω, ϕ) η^\prime$ decays; and (c) the pQCD predictions for the CP-violating asymmetries of the considered decays are generally not large in magnitude. The above predictions can be tested in the forthcoming LHC-b experiments at CERN.
We calculate the CP averaged branching ratios and CP-violating asymmetries for $B^0 \to ηη, ηη^\prime$ and $η^\prime η^\prime$ decays by employing the perturbative QCD (pQCD) factorization approach. The pQCD predictions for the CP-averaged branching ratios are $Br(B^0 \to ηη) \approx 0.67 \times 10^{-7}$, $Br(B^0 \to ηη^\prime) \approx 0.18 \times 10^{-7}$, and $Br(B^0 \to η^{\prime} η^{\prime}) \approx 0.11 \times 10^{-7}$, which are consistent with currently available experimental upper limits. We also predict large CP-violating asymmetries for the considered three decay modes, which can be tested by the future B meson experiments.
In this paper, we present the exact calculations for the vertex $\bar{s}γb$ and $\bar{s} Z b$ in the unitary gauge. We found that (a) the divergent- and $μ$-dependent terms are left in the effective vertex function $Γ^γ_μ(p,k)$ for $b \to s γ$ transition even after we sum up the contributions from four related Feynman diagrams; (b) for an on-shell photon, such terms do not contribute et al; (c) for off-shell photon, these terms will be canceled when the contributions from both vertex $\bar{s}γb$ and $\bar{s} Z b$ are taken into account simultaneously, and therefore the finite and gauge independent function $Z_0(x_t)=C_0(x_t)+ D_0(x_t)/4$, which governs the semi-leptonic decay $b \to s l^- l^+$, is derived in the unitary gauge.
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.
We calculate the new physics contributions to the branching ratios of the rare decays $B \to X_s l^+ l^-$ $(l=e, μ)$ induced by neutral Higgs bosons loop diagrams in the top quark two-Higgs-doublet model (T2HDM). From the numerical calculations, we find that (a) the neutral Higgs boson's correction to $B \to X_s l^+ l^-$ decays interferes constructively with its standard model counterpart, but small in magnitude; (b) the neutral Higgs contributions to the branching ratio of $B \to X_s l^+ l^-$ decay can be neglected safely if their masses are larger than 100 GeV and $\tanβ\leq 40$.
We calculate the new physics contributions to the neutral $B_d^0$ and $B_s^0$ meson mass splitting $ΔM_d$ and $ΔM_s$ induced by the box diagrams involving the charged-Higgs bosons in the top quark two-Higgs doublet model (T2HDM). Using the precision data, we obtain the bounds on the parameter space of the T2HDM: (a) for fixed $M_H=400$ GeV and $δ=[0^\circ,60^\circ]$, the upper bound on $\tanβ$ is $\tan β\leq 30$ after the inclusion of major theoretical uncertainties; (b) for the case of $\tanβ \leq 20$, a light charged Higgs boson with a mass around 300 GeV is allowed; and (c) the bounds on $\tanβ$ and $M_H$ are strongly correlated: a smaller (larger) $\tanβ$ means a lighter (heavier) charged Higgs boson.
We calculate the new physics contributions to the rare semileptonic decay $B \to X_s l^+ l^-$ $(l=e,μ)$ induced by the charged-Higgs loop diagrams appeared in the top quark two-Higgs doublet model (T2HDM). Within the considered parameter space, we found that (a) the effective Wilson coefficients $\widetilde{C}_{i}^{eff}(m_b)$ ($i =7γ, 9V$ and $10A$) in the T2HDM are always standard model like; (b) the new physics contributions to $\widetilde{C}_{7γ}^{eff}$ and $\widetilde{C}_{9V}^{eff}$ can be significant, but they tend to cancel each other; and (c) the T2HDM predictions for $Br(B \to X_s l^+ l^-)$ agree well with the measured value within one standard deviation.
In this paper, we calculate the branching ratios and CP-violating asymmetries for $B_{s}\to ρ^\pm K^\mp$, $B_{s}\toρ^{0}\bar{K}^0 $ and $B_{s}\toω\bar{K}^0$ decays in the perturbative QCD (pQCD) factorization approach. The theoretical predictions for the CP averaged branching ratios of the considered decays are: $Br(B_{s}\toρ^\pm K^\mp)\approx 24.7 \times 10^{-6}$, $Br(B_{s}\toρ^{0}\bar{K}^0) \approx 1.2 \times 10^{-7}$ and $Br(B_{s} \toω\bar{K}^0) \approx 1.7 \times 10^{-7}$; and we also predict very large direct CP-violating asymmetries for the latter two decay modes: $A_{CP}^{dir}(ρ^{\pm} K^{\mp})\approx -12 %$, $A_{CP}^{dir}(ρ^0\bar{K}^0)\approx -92%$, $A_{CP}^{dir}(ω^0\bar{K}^0)\approx 81%$, $A_{CP}^{mix}(ρ^0\bar{K}^0)\approx -36%$, and $A_{CP}^{mix}(ω^0\bar{K}^0) \approx -40%$, which can be tested in the forthcoming LHC-b experiments.
We calculate the branching ratios and CP-violating asymmetries for $B_s^0 \to π^0 η^{(\prime)}$ 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. The pQCD predictions for the CP-averaged branching ratios are $BR(B_s^0 \to π^0 η) \approx 0.86 \times 10^{-7}$ and $BR(B_s^0 \to π^0 η') \approx 1.86 \times 10^{-7}$. The pQCD predictions for the CP-violating asymmetries are $A_{CP}^{dir}(π^0 η)\sim -4.5 % $, $A_{CP}^{dir}(π^0 η')\sim -9.1% $, $A_{CP}^{mix}(π^0 η)\sim -0.2%$, and $A_{CP}^{mix}(π^0 η')\sim 27.0%$ but with large errors. The above pQCD predictions can be tested in the near future LHC-b experiments at CERN and the BTeV experiments at Fermilab.