arXiv subjects
Publications and source records attributed to Xing-Gang Wu.
In this paper, we investigate the phenomenologies of models where the Higgs sector plays the role of messengers in gauge mediation. The minimal Higgs sector and its extension are considered respectively. We find that there exist viable models when an appropriate parity is imposed. Phenomenological features in these kind of models include three sum rules for scalar masses, light gluino as well as one-loop $μ$ and two-loop $Bμ$ terms.
In Ref.[7],we have dealt with the production of the two color-singlet $S$-wave $(c\bar{b})$-quarkonium states $B_c(|(c\bar{b})_{\bf 1}[^1S_0]>)$ and $B^*_c(|(c\bar{b})_{\bf 1}[^3S_1]>)$ through the $Z^0$ boson decays. As an important sequential work, we make a further discussion on the production of the more complicated $P$-wave excited $(c\bar{b})$-quarkonium states, i.e. $|(c\bar{b})_{\bf 1}[^1P_1]>$ and $|(c\bar{b})_{\bf 1}[^3P_J]>$ (with $J=(1,2,3)$). More over, we also calculate the channel with the two color-octet quarkonium states $|(c\bar{b})_{\bf 8}[^1S_0]g>$ and $|(c\bar{b})_{\bf 8}[^3S_1]g>$, whose contributions to the decay width maybe at the same order of magnitude as that of the color-singlet $P$-wave states according to the naive nonrelativistic quantum chromodynamics scaling rules. The $P$-wave states shall provide sizable contributions to the $B_c$ production, whose decay width is about 20% of the total decay width $Γ_{Z^0\to B_c}$. After summing up all the mentioned $(c\bar{b})$-quarkonium states' contributions, we obtain $Γ_{Z^0\to B_c} =235.9^{+352.8}_{-122.0}$ KeV, where the errors are caused by the main uncertainty sources.
We investigate the hadronic production of the doubly heavy baryon $Ξ_{bc}$ at the large hadron collider (LHC), where contributions from the four $(bc)$-diquark states $(bc)_{\bf\bar{3},6}[^1S_0]$ and $(bc)_{\bf\bar{3},6}[^3S_1]$ have been taken into consideration. Numerical results show that under the condition of $p_T>4$ GeV and $|y|<1.5$, sizable $Ξ_{bc}$ events about $ 1.7\times 10^7$ and $3.5\times10^9$ per year can be produced for the center-of-mass energy $\sqrt{S}=7$ TeV and $\sqrt{S}=14$ TeV respectively. For experimental usage, the total and the interested differential cross-sections are estimated under some typical $p_T$- and $y$- cuts for the LHC detectors CMS, ATLAS and LHCb. Main uncertainties are discussed and a comparative study on the hadronic production of $Ξ_{cc}$, $Ξ_{bc}$ and $Ξ_{bb}$ at LHC are also presented.
We present an improved calculation on the pionic twist-3 distribution amplitudes $ϕ^π_{p}$ and $ϕ^π_σ$, which are studied within the QCD sum rules. By adding all the uncertainties in quadrature, it is found that $<ξ^2_p>=0.248^{+0.076}_{-0.052}$, $<ξ^4_p>=0.262^{+0.080}_{-0.055}$, $<ξ^2_σ>=0.102^{+0.035}_{-0.025}$ and $<ξ^4_σ>=0.094^{+0.028}_{-0.020}$. Furthermore, with the help of these moments, we construct a model for the twist-3 wave functions $ψ^π_{p,σ}(x,\mathbf{k}_\bot)$, which have better end-point behavior and are helpful for perturbative QCD approach. The obtained twist-3 distribution amplitudes are adopted to calculate the $B\toπ$ transition form factor $f^+_{Bπ}$ within the QCD light-cone sum rules up to next-to-leading order. By suitable choice of the parameters, we obtain a consistent $f^+_{Bπ}$ with those obtained in the literature.
We calculate the cross section of the exclusive process $e^{+} +e^{-}\to J/ψ+η_c$ at the leading order approximation within the QCD light-cone sum rules (LCSR) approach. It is found that the form factor $F_{VP}(V=J/ψ,P=η_c)$ depends mainly on the behavior of the twist-2 distribution amplitude of the $η_c$-meson at the scale of this process. Thus in order to obtain a reliable estimation of the cross section, it is important to have a realistic distribution amplitude of the $η_c$ meson, and to deal with the evolution of the distribution amplitude to the effective energy scale of the process. Our results show that one can obtain a compatible prediction with the Belle and BarBar experimental data.
The B-decay constant $f_B$ is an important component for studying $B$-meson decays, which can be studied through QCD sum rules. We make a detailed discussion on $f_B$ from two sum rules, i.e. sum rules I and II, which are derived from the conventional correlator and the correlator with chiral currents respectively. It is found that these two sum rules are consistent with each other. However, the sum rules II has less uncertainty sources than that of sum rules I, and then it can be more accurate if we know the dimension-four gluon condensate well. It is found that $f_B$ decreases with the increment of $m_b$, and to compare with the Belle experimental data on $f_B$, both sum rules prefer smaller pole $b$-quark mass, $m_b=4.68\pm0.07$ GeV. By varying all the input parameters in their reasonable region and adding all the uncertainties together in quadrature, we obtain $f_B=172^{+23}_{-25}$ MeV for sum rules I and $f_B=214_{-34}^{+26}$ MeV for sum rules II.
The programming new $e^{+}e^-$ collider with high luminosity shall provide another useful platform to study the properties of the doubly heavy $B_c$ meson in addition to the hadronic colliders as LHC and TEVATRON. Under the `New Trace Amplitude Approach', we calculate the production of the spin-singlet $B_c$ and the spin-triplet $B^*_c$ mesons through the $Z^0$ boson decays, where uncertainties for the production are also discussed. Our results show $Γ_{(^1S_0)}= 81.4^{+102.1}_{-40.5}$ KeV and $Γ_{(^3S_1)}=116.4^{+163.9}_{-62.8}$ KeV, where the errors are caused by varying $m_b$ and $m_c$ within their reasonable regions.
The new BABAR data on the pion-photon transition form factor arouses people's new interests on the determination of pion distribution amplitude. To explain the data, we take both the leading valence quark state's and the non-valence quark states' contributions into consideration, where the valence quark part up to next-to-leading order is presented and the non-valence quark part is estimated by a phenomenological model based on its limiting behavior at both $Q^2\to 0$ and $Q^2\to\infty$. Our results show that to be consistent with the new BABAR data at large $Q^2$ region, a broader other than the asymptotic-like pion distribution amplitude should be adopted. The broadness of the pion distribution amplitude is controlled by a parameter $B$. It has been found that the new BABAR data at low and high energy regions can be explained simultaneously by setting $B$ to be around 0.60, in which the pion distribution amplitude is closed to the Chernyak-Zhitnitsky form.
Considering the possibility to build an $e^+e^-$ collider at the energies around $Z$-boson resonance with a luminosity so high as ${\cal L} \propto 10^{34}cm^{-2}s^{-1}$ (even higher) and the abilities of a modern synthesis detector, we systematically calculate the exclusive two body processes: $e^+e^-$ annihilates into a heavy quarkonium and a photon (initiate state radiation i.e. ISR is involved), at the energies around the $Z$-boson resonance. Since the couplings of $Z$-boson to quarks contain axial vector as well as vector, so here the produced heavy quarkonium may stand for a charmonium such as ${J/ψ,η_c,h_c,χ_{cJ}}\cdots$ and a bottomonium such as ${Υ,η_b,h_b,χ_{bJ}}\cdots$ respectively. If we call such a collider with so high luminosity and running around the $Z$-boson resonance as a $Z$-factory, then our results obtained here indicate that experimental studies at a $Z$-factory about the various heavy quarkona (their ground and excited states) via the two-body processes, especially, the production of the bound states with quantum number $J^{PC}=1^{--}$ via ISR, have outstanding advantages.
An upgraded (second) version of the package GENXICC ({\bf A Generator for Hadronic Production of the Double Heavy Baryons $Ξ_{cc}$, $Ξ_{bc}$ and $Ξ_{bb}$ by C.H. Chang, J.X. Wang and X.G. Wu,} [its first version: in Comput. Phys. Commun. {\bf 177} (2007) 467-478]) is presented. Users, with this version being implemented in PYTHIA and a GNU C compiler, may simulate full events of the production in various experimental environments conveniently. In comparison with the previous version, in order to implement it in PYTHIA properly, a subprogram for the fragmentation of the produced double heavy diquark to the relevant baryon is complemented and the interphase of the generator to PYTHIA is changed accordingly. In the subprogram, with explanation, certain necessary assumptions (approximations) are made so as to conserve the momenta and the QCD `color' flow for the fragmentation.
Dominant spin-flip effects for the direct and prompt $J/ψ$ polarizations at TEVATRON run II with collision energy 1.96 TeV and rapidity cut $|y^{J/ψ}|<0.6$, have been systematically studied, especially, the spin-flip effect for the transition of $(c\bar{c})_8[^3S_1]$ into $J/ψ$ has been carefully discussed. It is found that the spin-flip effect shall always dilute the $J/ψ$ polarization, and with a suitable choice of the parameters $a_{0,1}$ and $c_{0,1,2}$, the $J/ψ$ polarization puzzle can be solved to a certain degree. At large transverse momentum $p_t$, $α$ for the prompt $J/ψ$ is reduced by $\sim50%$ for $f_0 = v^2$ and by $\sim80%$ for $f_0=1$. We also study the indirect $J/ψ$ polarization from the $b$-decays, which however is slightly affected by the same spin-flip effect and then shall provide a better platform to determine the color-octet matrix elements.
We study the hadronic production of $B_s$ and $B_s^*$ mesons within the fixed-flavor-number scheme, in which the dominant gluon-gluon fusion mechanism is dealt with by using the complete $α_s^4$ approach. Main theoretical uncertainties for $B_s$ and $B_s^*$ production at TEVATRON and LHC are presented. It is found that when $m_s$ increases by steps of 0.1 GeV, the integrated cross section of $B^{(*)}_s$ decreases by $80%-100%$, when $m_b$ increases by steps of 0.1 GeV, it changes to be $\sim 10%$. While the uncertainties caused by the parton distribution function and the factorization scale varies within the region of 1/5 to 1/3. Considering possible kinematic cut on the transverse momentum and the rapidity cut for the detectors at TEVATRON and LHC, we also make estimations on the $B_s$ and $B_s^*$ production with various kinematic cuts.
Based on the approach of the vector form factor $F^{+}_{B\toπ, K}(q^2)$ in our previous papers, we extend the calculation of the radiative corrections to the $B\to P$ ($P$ stands $π$, $K$ and all light pseudoscalar mesons) scalar and tensor form factors $F^{0,T}_{B\to P}(q^2)$ with chiral current in the light-cone sum rules (LCSRs). The most uncertain twist-3 contributions to the $B\to P$ form factors can be naturally eliminated through a properly designed correlator. We present the next-leading-order formulae of $F^{+,0,T}_{B\to P}(q^2)$ with the $b$-quark pole mass that is universal. It has been shown that our results are simpler and less uncertain under the same parameter regions since we only need to calculate the next leading order on the twist-2 part from the obtained LCSR. Second, we obtain $f^{+,0}_{B\toπ}(0)=0.260^{+0.059}_{-0.040}$, $f^{T}_{B\toπ}(0)=0.276^{+0.052}_{-0.039}$, $f^{+,0}_{B\to K}(0)=0.334^{+0.094}_{-0.069}$ and $f^{T}_{B\to K}(0) =0.379^{+0.092}_{-0.077}$ at $q^2=0$ and the $SU_f(3)$-breaking effects are discussed too.
The properties of the B-meson light-cone wave function up to next-to-leading order Fock state expansion have been studied through a comparative study of the $B\to π$, $K$ transition form factors within the $k_T$ factorization approach and the light-cone sum rule analysis. The transition form factors $F^{B\toπ}_{+,0,T}$ and $F^{B\to K}_{+,0,T}$ are carefully re-calculated up to ${\cal O}(1/m_b^2)$ within the $k_T$ factorization approach in the large recoil region, in which the main theoretical uncertainties are discussed. The QCD light-cone sum rule is applicable in the large and intermediate energy regions, and the QCD light-cone sum rule results in Ref.\cite{sumrule} are adopted for such a comparative study. It is found that when the two phenomenological parameters $\barΛ\in [0.50,0.55]$ and $δ\in[0.25,0.30]$, the results of $F^{B\toπ}_{+,0,T}(Q^2)$ and $F^{B\to K}_{+,0,T}(Q^2)$ from these two approaches are consistent with each other in the large recoil energy region.
Main theoretical uncertainties in estimating the indirect production of $(b\bar{c})$-quarkonium ($B^-_c$ meson and its excited states) via top quark decays, $t\to (b\bar{c})+c+W^{+}$, are studied within the non-relativistic QCD framework. It is found that the dimensionless reduced decay width for a particular $(b\bar{c})$-quarkonium state, $\barΓ_{n}=Γ_{n} /Γ_{t\to W^{+}+b}$, is very sensitive to the $c$-quark mass, while the uncertainties from the $b$-quark and $t$-quark masses are small, where $n$ stands for the eight $(b\bar{c})$-quarkonium states up to ${\cal O}(v^4)$: $|(b\bar{c})(^1S_0)_1>$, $|(b\bar{c})(^3S_1)_1>$, $|(b\bar{c})(^1P_1)_1>$, $|(b\bar{c})(^3P_J)_1>$ (with $J=(1,2,3)$), $|(b\bar{c})(^1S_0)_{8}g>$ and $|(b\bar{c})(^3S_1)_{8}g>$ respectively. About $10^8$ $t\bar{t}$-pairs shall be produced per year at CERN LHC, if adopting the assumption that all the higher Fock states decay to the ground state with 100% probability, then we shall have $(1.038^{+1.353}_{-0.782})\times 10^5$ $B^-_c $ events per year. So the indirect production provides another important way to study the properties of $B^-_c$ meson in comparison to that of the direct hadronic production at CERN LHC.
CERN LHC provides a good experimental platform to perturbatively probe the fundamental gravity scale up to several TeV, with the precise value depending on the number of extra dimensions. The leading experimental signal of graviton at LHC is from the process $pp\to jet+{E\slash}_T$, where ${E\slash}_T$ stands for the transverse missing energy. A detailed discussion on the hadronic production of real graviton through hard subprocesses: $q\bar{q}\to G+g$, $g+q\to G+q$ and $g+g\to G+g$ have been studied within the quantum gravity theory with large extra dimensions. The main theoretical uncertainties together with the dominant standard model background to these processes, e.g. $q\bar{q}\to Z^0+g$ and $g+q\to Z^0+q$ with $Z^0$ further decaying into neutrinos, have also been discussed. It is found that only in certain jet energy region and with certain number of extra dimensions can the quantum gravity signal be distinguished from the background, which inversely lead to the effective scale $M_D$ to be probed up to $(8.8\pm 0.9)$ TeV for two extra dimensions, and $(5.9\pm 0.5)$ TeV for four extra dimensions with sufficient integrated luminosity, e.g. $100fb^{-1}$, at CERN LHC.
We present an improved analysis of the constraints on the first two Gegenbauer moments, $a^π_2$ and $a^π_4$, of the pion's leading-twist distribution amplitude from a QCD light-cone sum rule analysis of $B\toπ$ weak transition form factor $f_{+}(q^2)$. Proper chiral current is adopted in QCD light-cone sum rule so as to eliminate the most uncertain twist-3 contributions to $f_{+}(q^2)$, and then we concentrate our attention on the properties of the leading-twist pion DA. A nearly model-independent $f_+(q^2)$ as shown in Ref.\cite{pball0} that is based on the spectrum of $B\toπlν$ decays from BaBar, together with their uncertainties, are adopted as the standard shape for $f_+(q^2)$ to do our discussion. From a minimum $χ^2$-fit and by taking the theoretical uncertainties into account, we obtain $a^π_2(1GeV)=0.17^{+0.15}_{-0.17}$ and $a^π_4(1GeV)=-0.06^{+0.20}_{-0.22}$ at the $1σ$ confidence level for $m^*_b\in[4.7,4,8] GeV$.
We present a systematical study on the kaon electromagnetic form factors $F_{K^{\pm},K^0,\bar{K}^0}(Q^2)$ within the $k_T$ factorization formalism, where the transverse momentum effects, the contributions from the different helicity components and different twist structures of the kaon light-cone (LC) wave function are carefully analyzed for giving a well understanding of the hard contributions at the energy region where pQCD is applicable. The right power behavior of the hard contribution from the higher helicity components and from the higher twist structures can be obtained by keeping the $k_T$ dependence in the hard amplitude. Our results show that the $k_T$ dependence in LC wave function affects the hard and soft contributions substantially and the power-suppressed terms (twist-3 and higher helicity components) make an important contribution below $Q^2\sim several GeV^2$ although they drop fast as $Q^2$ increasing. The parameters of the proposed model wave function can be fixed by the first two moments of its distribution amplitude and other conditions. By varying the first two moments $a^K_1(1GeV)$ and $a^K_2(1GeV)$ with the region of $0.05\pm0.02$ and $0.10\pm 0.05$ respectively, we find that the uncertainty of the kaon electromagnetic form factor is rather small.