arXiv subjects

Xing-Gang Wu

Publications and source records attributed to Xing-Gang Wu.

240 records · Page 14Linked to original sources

arXiv2005

B-Meson Wavefunction in the Wandzura-Wilczek Approximation

The B-meson wavefunction has been studied with the help of the vacuum-to-meson matrix element of the nonlocal operators in the heavy quark effective theory. In order to obtain the Wandzura-Wilczek-type B-meson wavefunction, we solve the equations which are derived from the equation of motion of the light spectator quark in the B meson by using two different assumptions. Under the condition that $ω_0=2\barΛ$, the solutions for the B-meson wavefunction in this paper agree well with the one obtained by directly taking the heavy quark limit $m_b\to\infty$. Our results show that the equation of motion of the light spectator quark in the B meson can impose a strong constraint on the B-meson wavefunctions $Ψ_\pm(ω,z^2)$. Based on the obtained results, we claim that both its distribution amplitudes $ϕ_B(ω)$ and $\barϕ_B(ω)$ are important for calculating the B meson decays.

hep-ph↗

arXiv2004

A Model for the Twist-3 Wave Function of the Pion and Its Contribution to the Pion Form Factor

A model for the twist-3 wave function $ψ_p(x,\mathbf{k_\perp})$ of the pion has been constructed based on the moment calculation by applying the QCD sum rules, whose distribution amplitude has a better end-point behavior than that of the asymptotic one. With this model wave function, the twist-3 contributions including both the usual helicity components ($λ_1+λ_2=0$) and the higher helicity components ($λ_1+λ_2=\pm 1$) to the pion form factor have been studied within the modified pQCD approach. Our results show that the twist-3 contribution drops fast and it becomes less than the twist-2 contribution at $Q^2\sim 10GeV^2$. The higher helicity components in the twist-3 wave function will give an extra suppression to the pion form factor. The model dependence of the twist-3 contribution to the pion form factor has been studied by comparing three different models. When all the power contributions, which include higher order in $α_s$, higher helicities, higher twists in DA and etc., have been taken into account, it is expected that the hard contributions will fit the present experimental data well at the energy region where pQCD is applicable.

hep-ph↗

arXiv2004

Hadronic production of the $P$-wave excited $B_c$-states ($B_{cJ,L=1}^*$)

Adopting the complete $α_s^4$ approach of the perturbative QCD (pQCD) and updated parton distribution functions, we have estimated the hadronic production of $P$-wave excited $B_c$-states ($B_{cJ,L=1}^*$). In the estimate, special care on the relation of the production amplitude to the derivative of wave function at origin of the potential model is payed. For experimental references, main uncertainties are discussed, and the total cross sections and the distributions of the production with reasonable cuts at the energies of Tevatron and LHC are computed and presented. The results show that $P$-wave production may contribute to the $B_c$-meson production indirectly by a factor about 0.5 of the direct production, and with such a big cross section, it is worth further to study the possibility to observe the $P$-wave production itself experimentally.

hep-ph↗

arXiv2004

Uncertainties in Estimating Hadronic Production of the Meson B_c and Comparisons between TEVATRON and LHC

The uncertainties in estimating the hadronic production of the $B_c$ meson are studied under the framework of the complete $α_s^4$ approach of the perturbative QCD and the gluon-gluon fusion mechanism. Quantitative comparisons on the production at TEVATRON and LHC are made. Considering the detectors at TEVATRON and LHC, we have also estimated the production with proper kinematic cuts. Based on the results, we conclude that the experimental studies of the $B_c$ meson at the two colliders will be complimentary and stimulative. We find that as c.m. energy is increasing from RUN-I to RUN-II at TEVATRON, the production cross-section increases about 20%.

hep-ph↗

arXiv2003

BCVEGPY: An Event Generator for Hadronic Production of the B_c Meson

We have written a Fortran programme BCVEGPY, which is an event generator for the hadronic production of the $B_c$ meson through the dominant hard subprocess $gg\to B_c(B_c^*) +b+\bar{c}$. To achieve a compact programme, we have written the amplitude of the subprocess with the particle helicity technique and made it as symmetric as possible, by decomposing the gluon self couplings and then applying the symmetries. To check the programme, various cross sections of the subprocess have been computed numerically and compared with those in the literature. BCVEGPY is written in a PYTHIA-compatible format, thus it is easy to implement in PYTHIA.

hep-ph↗

arXiv2002

The meson $B_c$ annihilation to leptons and inclusive light hadrons

The annihilation of the $B_c$ meson to leptons and inclusive light hadrons is analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find that the decay mode, which escapes from the helicity suppression, contributes a sizable fraction width. According to the analysis, the branching ratio due to the contribution from the color-singlet component of the meson $B_c$ can be of order (10^{-2}). We also estimate the contributions from the color-octet components. With the velocity scaling rule of NRQCD, we find that the color-octet contributions are sizable too, especially, in certain phase space of the annihilation they are greater than (or comparative to) the color-singlet component. A few observables relevant to the spectrum of charged lepton are suggested, that may be used as measurements on the color-octet and color-singlet components in the future $B_c$ experiments. A typical long distance contribution in the annihilation is estimated too.

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