arXiv subjects

Xing-Gang Wu

Publications and source records attributed to Xing-Gang Wu.

At least 235 records · Page 13Linked to original sources

arXiv2008

SU_f(3)-Symmetry Breaking Effects of the B\to K Transition Form Factor in the QCD Light-Cone Sum Rules

We present an improved calculation of the $B\to K$ transition form factor with chiral current in the QCD light-cone sum rule (LCSR) approach. Under the present approach, the most uncertain twist-3 contribution is eliminated. And the contributions from the twist-2 and the twist-4 structures of the kaon wave function are discussed, including the $SU_f(3)$-breaking effects. One-loop radiative corrections to the kaonic twist-2 contribution together with the leading-order twist-4 corrections are studied. The $SU_f(3)$ breaking effect is obtained, $ \frac{F^{B\to K}_{+}(0)}{F^{B\toπ}_{+}(0)}=1.16\pm 0.03$. By combining the LCSR results with the newly obtained perturbative QCD results that have been calculated up to ${\cal O}(1/m^2_b)$ in Ref.\cite{hwf0}, we present a consistent analysis of the $B\to K$ transition form factor in the large and intermediate energy regions.

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arXiv2008

$B\to K$ Transition Form Factor with Tensor Current within the $k_T$ Factorization Approach

In the paper, we apply the $k_T$ factorization approach to deal with the $B\to K$ transition form factor with tensor current in the large recoil regions. Main uncertainties for the estimation are discussed and we obtain $F_T^{B\to K}(0)=0.25\pm0.01\pm0.02$, where the first error is caused by the uncertainties from the pionic wave functions and the second is from that of the B-meson wave functions. This result is consistent with the light-cone sum rule results obtained in the literature.

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arXiv2008

Semileptonic $B(B_s, B_c)$ decays in the light-cone QCD sum rules

Semileptonic $B$($B_s, B_c$) decays are investigated systematically in the light-cone QCD sum rules. Special emphasis is put on the LCSR calculation on weak form factors with an adequate chiral current correlator, which turns out to be particularly effective to control the pollution by higher twist components of spectator mesons. The result for each channel depends on the distribution amplitude of the the producing meson. The leading twist distribution amplitudes of the related heavy mesons and charmonium are worked out by a model approach in the reasonable way. A practical scenario is suggested to understand the behavior of weak form factors in the whole kinematically accessible ranges. The decay widths and branching ratios are estimated for several $B$($B_c$) decay modes of current interest.

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arXiv2007

Production of $B_c$ or $\bar{B}_c$ meson and its excited states via $\bar{t}$-quark or $t$-quark decays

The production of $(b\bar{c})$-quarkonium ($\bar{B}_c$ meson and its excited states) or $(c\bar{b})$-quarkonium ($B_c$ meson and its excited states) via top quark $t$ or top anti-quark $\bar{t}$ decays, $t\to (b\bar{c})+c+W^+$ or $\bar{t}\to (c\bar{b})+\bar{c}+W^-$, respectively is studied within the framework of NRQCD. In addition to the production of the two color-singlet $S$-wave states $|(b\bar{c})(^1S_0)_{\bf 1}>$ or $|(c\bar{b})(^1S_0)_{\bf 1}>$ and $|(b\bar{c})(^3S_1)_{\bf 1}>$ or $|(c\bar{b})(^3S_1)_{\bf 1}>$, the production of the $P$-wave excited $(b\bar{c})$ or $(c\bar{b})$ states, i.e. the four color-singlet $P$-wave states $|(b\bar{c})(^1P_1)_{\bf 1}>$ or $|(c\bar{b})(^1P_1)_{\bf 1}>$, and $(b\bar{c})(^3P_J)_{\bf 1}>$ or $(c\bar{b})(^3P_J)_{\bf 1}>$ (with $J=(1,2,3)$), is also studied. According to the velocity scaling rule of NRQCD, for the production of $P$-wave excited states the contributions from the two color-octet components $|(b\bar{c})(^1S_0)_{\bf 8}>$ or $|(c\bar{b})(^1S_0)_{\bf 8}>$ and $|(b\bar{c})(^3S_1)_{\bf 8}>$ or $|(c\bar{b})(^3S_1)_{\bf 8}>$ are also taken into account. We quantitatively discuss the possibility and the advantages in experimental studies of $B_c$ or $\bar{B}_c$ meson and its excited states via the indirect production at LHC in high luminosity runs and at LHC possible upgraded versions such as SLHC, DLHC, TLHC etc. in future.

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arXiv2007

$B\to K$ Transition Form Factor up to ${\cal O}(1/m^2_b)$ within the $k_T$ Factorization Approach

In the paper, we apply the $k_T$ factorization approach to deal with the $B\to K$ transition form factor $F^{B\to K}_{+,0}(q^2)$ in the large recoil regions. The B-meson wave functions $Ψ_B$ and $\barΨ_B$ that include the three-particle Fock states' contributions are adopted to give a consistent PQCD analysis of the form factor up to ${\cal O} (1/m^2_b)$. It has been found that both the wave functions $Ψ_B$ and $\barΨ_B$ can give sizable contributions to the form factor and should be kept for a better understanding of the $B$ meson decays. Then the contributions from different twist structures of the kaon wavefunction are discussed, including the $SU_f(3)$-breaking effects. A sizable contribution from the twist-3 wave function $Ψ_p$ is found, whose model dependence is discussed by taking two group of parameters that are determined by different distribution amplitude moments obtained in the literature. It is also shown that $F^{B\to K}_{+,0}(0)=0.30\pm0.04$ and $[F^{B\to K}_{+,0}(0)/F^{B\to π}_{+,0}(0)]=1.13\pm0.02$, which are more reasonable and consistent with the light-cone sum rule results in the large recoil regions.

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arXiv2007

Fragmentation Function and Hadronic Production of the Heavy Supersymmetric Hadrons

The light top-squark $\sto$ may be the lightest squark and its lifetime may be `long enough' in a kind of SUSY models which have not been ruled out yet experimentally, so colorless `supersymmetric hadrons (superhadrons)' $(\sto \bar{q})$ ($q$ is a quark except $t$-quark) may be formed as long as the light top-squark $\sto$ can be produced. Fragmentation function of $\sto$ to heavy `supersymmetric hadrons (superhadrons)' $(\sto \bar{Q})$ ($\bar{Q}=\bar{c}$ or $\bar{b}$) and the hadronic production of the superhadrons are investigated quantitatively. The fragmentation function is calculated precisely. Due to the difference in spin of the SUSY component, the asymptotic behavior of the fragmentation function is different from those of the existent ones. The fragmentation function is also applied to compute the production of heavy superhadrons at hadronic colliders Tevatron and LHC under the so-called fragmentation approach. The resultant cross-section for the heavy superhadrons is too small to observe at Tevatron, but great enough at LHC, even when all the relevant parameters in the SUSY models are taken within the favored region for the heavy superhadrons. The production of `light superhadrons' $(\sto \bar{q})$ ($q=u, d, s$) is also roughly estimated. It is pointed out that the production cross-sections of the light superhadrons $(\sto \bar{q})$ may be much greater than those of the heavy superhadrons, so that even at Tevatron the light superhadrons may be produced in great quantities.

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arXiv2007

GENXICC: A Generator for Hadronic Production of the Double Heavy Baryons $Ξ_{cc}$, $Ξ_{bc}$ and $Ξ_{bb}$

We write down a generator program for the hadronic production of the double-heavy baryons $Ξ_{cc}$, $Ξ_{bc}$ and $Ξ_{bb}$ according to relevant publications. We name it as GENXICC and we test it by comparing its numerical results with those in references. It is written in a PYTHIA-compatible format and it can be easily implemented into PYTHIA. GENXICC is also written in modularization manner, with {\bf make}, a GNU C compiler, one may apply the generator to various situations or experimental environments very conveniently.

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arXiv2007

Hadronic Production of the Doubly Charmed Baryon $Ξ_{cc}$ with Intrinsic Charm

The effects of the intrinsic charm on the hadronic production of $Ξ_{cc}$ are studied. By taking reasonable intrinsic charm component into account, the change of the theoretical prediction on the production of $Ξ_{cc}$ for LHC and Tevatron is small, but in contrast it may enhance significantly for SELEX. The reason is that the collision energy at LHC and Tevatron is so large that the gluon-gluon fusion sub-process, which is irrelevant to intrinsic charm, becomes dominant. But the situation for SELEX is quite different. Our numerical results for SELEX show that by considering all the contributions from various sub-processes, the predicted cross-section may be enhanced by a factor so big as $10^2$ due to a modulating intrinsic charm being taken into account. Therefore, the hadronic production of $Ξ_{cc}$ at SELEX may be sensitive enough in observing the intrinsic charm inside the incident hadrons.

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arXiv2007

Determination of the $η$ and $η'$ Mixing Angle from the Pseudoscalar Transition Form Factors

The possible range of $η-η'$ mixing angle is determined from the transition form factors $F_{ηγ}(Q^2)$ and $F_{η' γ}(Q^2)$ with the help of the present experimental data. For such purpose, the quark-flavor mixing scheme is adopted and the pseudoscalar transition form factors are calculated under the light-cone pQCD framework, where the transverse momentum corrections and the contributions beyond the leading Fock state have been carefully taken into consideration. We construct a phenomenological expression to estimate the contributions to the form factors beyond the leading Fock state based on their asymptotic behavior at $Q^2\to 0$ and $Q^2\to\infty$. By taking the quark-flavor mixing scheme, our results lead to $ϕ= 38.0^{\circ}\pm 1.0^{\circ}\pm 2.0^{\circ}$, where the first error coming from experimental uncertainty and the second error coming from the uncertainties of the wavefunction parameters. The possible intrinsic charm component in $η$ and $η'$ is discussed and our present analysis also disfavors a large portion of intrinsic charm component in $η$ and $η'$, e.g. $|f^c_{η'}|\le 50 {\rm MeV}$.

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arXiv2006

A Comprehensive Analysis on the Pion-Photon Transition Form Factor Beyond the Leading Fock State

We perform a comprehensive analysis of the pion-photon transition form factor $F_{πγ}(Q^2)$ involving the transverse momentum corrections with the present CLEO experimental data, in which the contributions beyond the leading Fock state have been taken into consideration. As is well-known, the leading Fock-state contribution dominates of $F_{πγ}(Q^2)$ at large momentum transfer ($Q^2$) region. One should include the contributions beyond the leading Fock state in small $Q^2$ region. In this paper, we construct a phenomenological expression to estimate the contributions beyond the leading Fock state based on its asymptotic behavior at $Q^2\to0$. Our present theoretical results agree well with the experimental data in the whole $Q^2$ region. Then, we extract some useful information of the pionic leading twist-2 distribution amplitude (DA) by comparing our results of $F_{πγ}(Q^2)$ with the CLEO data. By taking best fit, we have the DA moments, $a_2(μ_0^2)=0.002^{+0.063}_{-0.054}$, $a_4(μ_0^2)=-0.022_{-0.012}^{+0.026}$ and all of higher moments, which are closed to the asymptotic-like behavior of the pion wavefunction.

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arXiv2006

An Upgraded Version of the Generator BCVEGPY2.0 for Hadronic Production of $B_c$ Meson and Its Excited States

An upgraded version of the package [BCVEGPY2.0: Chao-Hsi Chang, Jian-Xiong Wang and Xing-Gang Wu, Comput. Phys. Commun. {\bf 174} (2006) 241-251] is presented, which works under LINUX system and is named as BCVEGPY2.1. Using this version with a GNU C compiler, users may simulate the $B_c$-events in various experimental environments very conveniently. It has been rearranged for better modularity and code reusability (less dependency among various modules) than BCVEGPY2.0 has. Furthermore, in the upgraded version a special and convenient executable-file {\bf run} as default is available according to one's wish, i.e., the file is obtained in the way that the GNU command {\bf make} compiles the codes requested by precise purpose with the help of a master {\bf makefile} in the main code directory. Finally, this paper may also be considered as an erratum of the original BCVEGPY2.0, i.e., here the errors (typo mainly) in BCVEGPY2.0 have been corrected.

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arXiv2006

B-Meson Wavefunction with Contributions from 3-particle Fock States

The B-meson light-cone wavefunctions, $Ψ_{\pm}(ω,z^2)$, are investigated up to the next-to-leading order in Fock state expansion in the heavy quark limit. In order to know the transverse momentum dependence of the B-meson wavefunctions with 3-particle Fock states' contributions, we make use of the relations between 2- and 3- particle wavefunctions derived from the QCD equations of motion and the heavy quark symmetry, especially two constraints derived from the gauge field equation of motion are employed. Our results show that the use of gluon equation of motion can give a constraint on the transverse momentum dependence $χ(ω,\mathbf{k}_\perp)$ of the B-meson wavefunctions, whose distribution tends to be a hyperbola-like curve under the condition $0<c_1<1$, which is quite different from the WW type wavefunctions, whose transverse momentum dependence $χ^{WW}(ω,\mathbf{k}_\perp)$ is merely a delta function. Based on the derived results, we propose a simple model for the B-meson wavefunctions with 3-particle Fock states' contributions.

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arXiv2006

Estimate of the Hadronic Production of the Doubly Charmed Baryon $Ξ_{cc}$ under GM-VFN Scheme

Hadronic production of the doubly charmed baryon $Ξ_{cc}$ ($Ξ^{++}_{cc}$ and $Ξ^{+}_{cc}$) is investigated under the general-mass variable-flavor-number (GM-VFN) scheme. The gluon-gluon fusion mechanism and the intrinsic charm mechanisms, i.e. via the sub-processes $g+g\to(cc)[^3S_1]_{\bar 3}+\bar{c}+\bar{c}$, $g+g\to(cc)[^1S_0]_6+\bar{c}+\bar{c}$; $g+c\to (cc)[^3S_1]_{\bar 3}+\bar{c}$, $g+c\to (cc)[^1S_0]_6+\bar{c}$ and $c+c\to (cc)[^3S_1]_{\bar 3}+g$, $c+c\to (cc)[^1S_0]_6+g$, are taken into account in the investigation, where $(cc)[^3S_1]_{\bar 3}$ (in color {\bf $\bar 3$}) and $(cc)[^1S_0]_6$ (in color {\bf 6}) are two possible $S$-wave configurations of the doubly charmed diquark pair $(cc)$ inside the baryon $Ξ_{cc}$. Numerical results for the production at hadornic colliders LHC and TEVATRON show that both the contributions from the doubly charmed diquark pairs $(cc)[^1S_0]_6$ and $(cc)[^3S_1]_{\bar 3}$ are sizable with the assumption that the two NRQCD matrix elements are equal, and the total contributions from the `intrinsic' charm mechanisms are bigger than those of the gluon-gluon fusion mechanism. For the production in the region of small transverse-momentum $p_t$, the intrinsic mechanisms are dominant over the gluon-gluon fusion mechanism and they can raise the theoretical prediction of the $Ξ_{cc}$ by almost one order.

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arXiv2005

Hadronic Production of $B_c(B^*_c)$ Meson Induced by the Heavy Quarks inside the Collision Hadrons

In general-mass variable-flavor-number (GM-VFN) scheme, the `heavy quark mechanisms' of $B_c(B_c^*)$ meson hadroproduction via the sub-processes $g+c\to B_c(B_c^*)+...$ and $g+\bar{b}\to B_c(B_c^*)+...$ are investigated. In the scheme, possible double counting from these mechanisms and the `light mechanisms' (the gluon-gluon fusion and quark-antiquark annihilation mechanisms) is subtracted properly. The numerical results show that the transverse momentum, $p_t$, distribution of the produced $B_c(B_c^*)$ from the `intrinsic heavy quark mechanisms' (i.e. the heavy quark mechanisms in which the double counting components have been subtracted accordingly) declines faster with the increment of the $p_t$ than that from the `light mechanisms', and only in small $p_t$ region ($p_t\lesssim 7.0$ GeV) the `intrinsic heavy quark mechanisms' themselves may make remarkable contributions. The combined contributions from the `intrinsic heavy quark mechanisms' and the `light mechanisms' to the production are compared with that obtained by the most calculations in literature, which in some sense are within the fixed flavor number (FFN) scheme at leading order, and we find that the production by virtue of the GM-VFN scheme is more or less the same as the one in literature, except in the small $p_t$ region.

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arXiv2005

Pion Electromagnetic Form Factor in the $K_T$ Factorization Formulae

Based on the light-cone (LC) framework and the $k_T$ factorization formalism, the transverse momentum effects and the different helicity components' contributions to the pion form factor $F_π(Q^2)$ are recalculated. In particular, the contribution to the pion form factor from the higher helicity components ($λ_1+λ_2=\pm 1$), which come from the spin-space Wigner rotation, are analyzed in the soft and hard energy regions respectively. Our results show that the right power behavior of the hard contribution from the higher helicity components can only be obtained by fully keeping the $k_T$ dependence in the hard amplitude, and that the $k_T$ dependence in LC wavefunction affects the hard and soft contributions substantially. A model for the twist-3 wavefunction $ψ_p(x,\mathbf{k_\perp})$ 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 wavefunction, 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 wavefunction will give an extra suppression to the pion form factor. 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.

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arXiv2005

BCVEGPY2.0: A upgrade version of the generator BCVEGPY with an addendum about hadroproduction of the $P$-wave $B_c$ states

The generator BCVEGPY is upgraded by adding the hadroproduction of the $P$-wave excited $B_c$ states (denoted by $B_{cJ,L=1}^*$ or by $h_{B_c}$ and $χ_{B_c}$) and by improving some features of the original one as well. We denote it as BCVEGPY2.0. The $P$-wave production is also calculated by taking only the dominant gluon-gluon fusion mechanism (with the subprocess $gg\to B_{cJ,L=1}^*+\bar{c}+b$ being dominated) into account as that for $S$-wave. In order to make the addendum piece of the upgraded generator as compact as possible so as to increase its efficiency, we manipulate the amplitude as compact as possible with FDC (a software for generating Feynman diagrams and the algebra amplitudes, and for manipulating algebra formulae analytically etc) and certain simplification techniques. The correctness of the program is tested by checking the gauge invariance of the amplitude and by comparing the numerical results with the existent ones in the literature carefully.

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arXiv2005

The Color-Octet Contributions to $P$-wave $B_c$ Meson Hadroproduction

The contributions from the color-octet components $|(c\bar b)_{\bf 8}(^{1}S_{0}) g>$ and $|(c\bar b)_{\bf 8}(^{3}S_{1}) g>$ to the $h_{B_c}$ or $χ_{B_c}^J$ (the $P$-wave $B_c$ meson) hadroproduction are estimated in terms of the complete ${\cal O}(α_s^4)$ calculation. As necessary inputs in the estimate, we take the values of the octet matrix elements according to the NRQCD scaling rules, and as a result, we have found that the contributions to the $P$-wave production may be the same in order of magnitude as those from the color-singlet ones, $|(c\bar b)_{\bf 1}(^{1}P_{1})>$ and $|(c\bar b)_{\bf 1}(^{3}P_{J})>$ ($J=1,2,3$). Especially, our result indicates that the observation of the color-octet contributions to the $P$-wave production in the low transverse momentum region is not very far from the present experimental capability at Tevatron and LHC.

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arXiv2005

Consistent Analysis of the $B\toπ$ Transition Form Factor in the Whole Physical Region

In the paper, we show that the $B\toπ$ transition form factor can be calculated by using the different approach in the different $q^2$ regions and they are consistent with each other in the whole physical region. For the $B\toπ$ transition form factor in the large recoil regions, one can apply the PQCD approach, where the transverse momentum dependence for both the hard scattering part and the non-perturbative wavefunction, the Sudakov effects and the threshold effects are included to regulate the endpoint singularity and to derive a more reliable PQCD result. Pionic twist-3 contributions are carefully studied with a better endpoint behavior wavefunction for $Ψ_p$ and we find that its contribution is less than the leading twist contribution. Both the two wavefunctions $Ψ_B$ and $\barΨ_B$ of the B meson can give sizable contributions to the $B\toπ$ transition form factor and should be kept for a better understanding of the B decays. The present obtained PQCD results can match with both the QCD light-cone sum rule results and the extrapolated lattice QCD results in the large recoil regions.

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