arXiv subjects

Tao Zhong

Publications and source records attributed to Tao Zhong.

99 records · Page 6Linked to original sources

arXiv2014

$V_{cb}$ from the semileptonic decay $B\to D \ell \barν_{\ell}$ and the properties of the $D$ meson distribution amplitude

The improved QCD light-cone sum rule (LCSR) provides an effective way to deal with the heavy-to-light transition form factors (TFFs). Firstly, we adopt the improved LCSR approach to deal with the $B\to D$ TFF $f^{+}(q^2)$ up to twist-4 accuracy. Due to the elimination of the most uncertain twist-3 contribution and the large suppression of the twist-4 contribution, the obtained LCSR shall provide us a good platform for testing the $D$-meson leading-twist DA. For the purpose, we suggest a new model for the $D$-meson leading-twist DA ($ϕ_{3D}$), whose longitudinal behavior is dominantly determined by a parameter $B$. Moreover, we find its second Gegenbauer moment $a^D_2\sim B$. Varying $B$ within certain region, one can conveniently mimic the $D$-meson DA behavior suggested in the literature. Inversely, by comparing the estimations with the experimental data on the $D$-meson involved processes, one can get a possible range for the parameter $B$ and a determined behavior for the $D$-meson DA. Secondly, we discuss the $B\to D$ TFF at the maximum recoil region and present a detailed comparison of it with the pQCD estimation and the experimental measurements. Thirdly, by applying the LCSR on $f^{+}(q^2)$, we study the CKM matrix element $\Vcb$ together with its uncertainties by adopting two types of processes, i.e. the $B^0/\bar{B}^0$-type and the $B^{\pm}$-type. It is noted that a smaller $B \precsim 0.20$ shows a better agreement with the experimental value on $\Vcb$. For example, for the case of $B=0.00$, we obtain $|V_{cb}|(B^0/\bar{B}^0-{\rm type})=(41.28 {^{+5.68}_{-4.82}} {^{+1.13}_{-1.16}}) \times 10^{-3}$ and $|V_{cb}|(B^{\pm}-{\rm type})=(40.44 {^{+5.56}_{-4.72}} {^{+0.98}_{-1.00}}) \times 10^{-3}$, whose first (second) uncertainty comes from the squared average of the mentioned theoretical (experimental) uncertainties.

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arXiv2013

Determination of the pion distribution amplitude

Right now, we have not enough knowledge to determine the hadron distribution amplitudes (DAs) which are universal physical quantities in the high energy processes involving hadron for applying pQCD to exclusive processes. Even for the simplest pion, one can't discriminate from different DA models. Inversely, one expects that processes involving pion can in principle provide strong constraints on the pion DA. For example, the pion-photon transition form factor (TFF) can get accurate information of the pion wave function or DA, due to the single pion in this process. However, the data from Belle and BABAR have a big difference on TFF in high $Q^2$ regions, at present, they are helpless for determining the pion DA. At the present paper, we think it is still possible to determine the pion DA as long as we perform a combined analysis of the most existing data of the processes involving pion such as $π\to μ\barν$, $π^0 \to γγ$, $B\to πl ν$, $D \to πl ν$, and etc. Based on the revised light-cone harmonic oscillator model, a convenient DA model has been suggested, whose parameter $B$ which dominates its longitudinal behavior for $ϕ_π(x,μ^2)$ can be determined in a definite range by those processes. A light-cone sum rule analysis of the semi-leptonic processes $B \to πl ν$ and $D \to πl ν$ leads to a narrow region $B = [0.01,0.14]$, which indicate a slight deviation from the asymptotic DA. Then, one can predict the behavior of the pion-photon TFF in high $Q^2$ regions which can be tested in the future experiments. Following this way it provides the possibility that the pion DA will be determined by the global fit finally.

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arXiv2013

Twist-3 light-cone distribution amplitudes of the scalar mesons within the QCD sum rules and their application to the $B \to S$ transition form factors

We investigate the twist-3 light-cone distribution amplitudes (LCDAs) of the scalar mesons $a_0$, $K^{\ast}_0$ and $f_0$ within the QCD sum rules. The QCD sum rules are improved by a consistent treatment of the sizable $s$-quark mass effects within the framework of the background field approach. Adopting the valence quark component $(\bar{q}_1 q_2)$ as the dominant structure of the scalar mesons, our estimation for their masses are close to the measured $a_0(1450)$, $K^{\ast}_0(1430)$ and $f_0(1710)$. From the sum rules, we obtain the first two non-zero moments of the twist-3 LCDAs $ϕ^{s,σ}_{a_0}$: $\langle ξ_{s,a_0}^{2(4)} \rangle=0.369 \;(0.245)$ and $\langle ξ_{σ,a_0}^{2(4)} \rangle=0.203 \;(0.093)$; those of the twist-3 LCDAs $ϕ_{K^*_0}^{s,σ}$: $\langle ξ_{s,K^{\ast}_0}^{1(2)} \rangle =0.004\;(0.355)$ and $\langle ξ_{σ,K^{\ast}_0}^{1(2)} \rangle =0.018\;(0.207)$; and those of the twist-3 LCDAs $ϕ_{f_0}^{s,σ}$: $\langle ξ_{s,f_0}^{2(4)} \rangle=0.335 \;(0.212)$ and $\langle ξ_{σ,f_0}^{2(4)} \rangle=0.196 \; (0.088)$, respectively. As an application of those twist-3 LCDAs, we study the $B \to S$ transition form factors by introducing proper chiral currents into the correlator, which is constructed such that the twist-3 LCDAs give dominant contribution and the twist-2 LCDAs make negligible contribution. Our results of the $B \to S$ transition form factors at the large recoil region $q^2 \simeq 0$ are consistent with those obtained in the literature, which inversely shows the present twist-3 LCDAs are acceptable.

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arXiv2013

Finding a way to determine the pion distribution amplitude from the experimental data

It is believed that one can extract more accurate information of the pion distribution amplitude from the pion-photon transition form factor (TFF) due to the single pion in this process. However the BABAR and Belle data of the pion-photon TFF have a big difference for $Q^2\in [15,40]$ GeV$^2$, and at present, the pion DA can not be definitely determined from the pion-photon TFF. it is crucial to find the right pion DA behavior and to determine which data is more reliable. In this letter, we perform a combined analysis of the most existing data of the processes involving pion by using a general model for the pion wavefunction/DA. Such a DA model can mimic all the existed pion DA behaviors, whose parameters can be fixed by the constraints from the processes $π^0\toγγ$, $π\toμν$, $B\toπl ν$, and etc. Especially, we examine the $B \rightarrow π$ transition form factors that provides another constraint to the parameter $B$ in our DA model, which results in $B \in[0.00,0.29]$. This inversely shows that the predicted curve for the pion-photon TFF is between the BABAR and Belle data in the region $Q^2\in$ $[15,40]$ GeV$^2$. It will be tested by coming more accurate data at large $Q^2$ region, and the definite behavior of pion DA can be concluded finally.

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arXiv2012

Information on the Pion Distribution Amplitude from the Pion-Photon Transition Form Factor with the Belle and BaBar Data

The pion-photon transition form factor (TFF) provides strong constraints on the pion distribution amplitude (DA). We perform an analysis of all existing data (CELLO, CLEO, BaBar, Belle) on the pion-photon TFF by means of light-cone pQCD approach in which we include the next-to-leading order correction to the valence-quark contribution and estimate the non-valence-quark contribution by a phenomenological model based on the TFF's limiting behavior at both $Q^2\to 0$ and $Q^2\to\infty$. At present, the pion DA is not definitely determined, it is helpful to have a pion DA model that can mimic all the suggested behaviors, especially to agree with the constraints from the pion-photon TFF in whole measured region within a consistent way. For the purpose, we adopt the conventional model for pion wavefunction/DA that has been constructed in our previous paper \cite{hw1}, whose broadness is controlled by a parameter $B$. We fix the DA parameters by using the CELLO, CLEO, BABAR and Belle data within the smaller $Q^2$ region ($Q^2 \leq 15$ GeV$^2$), where all the data are consistent with each other. And then the pion-photon TFF is extrapolated into larger $Q^2$ region. We observe that the BABAR favors $B=0.60$ which has the behavior close to the Chernyak-Zhitnitsky DA, whereas the recent Belle favors $B=0.00$ which is close to the asymptotic DA. We need more accurate data at large $Q^2$ region to determine the precise value of $B$, and the definite behavior of pion DA can be concluded finally by the consistent data in the coming future.

hep-ph↗

arXiv2012

Revisiting the Twist-3 Distribution Amplitudes of $K$ Meson within the QCD Background Field Approach

In the present paper, we investigate the kaon twist-3 distribution amplitudes (DAs) $ϕ_{p,σ}^K$ within the QCD background field approach. The $SU_f(3)$-breaking effects are studied in detail under a systematical way, especially the sum rules for the moments of $ϕ_{p,σ}^K$ are obtained by keeping all the mass terms in the $s$-quark propagator consistently. After adding all the uncertainties in quadrature, the first two Gegenbauler moments of $ϕ_{p,σ}^K$ are $a^1_{K,p}(1 {\rm GeV}) = -0.376^{+0.103}_{-0.148}$, $a^2_{K,p}(1 {\rm GeV}) = 0.701^{+0.481}_{-0.491}$, $a^1_{K,σ}(1 {\rm GeV}) = -0.160^{+0.051}_{-0.074}$ and $a^2_{K,σ}(1 {\rm GeV}) = 0.369^{+0.163}_{-0.149}$, respectively. Their normalization parameters $μ_K^p |_{1\rm GeV} = 1.188^{+0.039}_{-0.043}$ GeV and $μ_K^σ|_{1\rm GeV} = 1.021^{+0.036}_{-0.055}$ GeV. A detailed discussion on the properties of $ϕ^K_{p,σ}$ moments shows that the higher-order $s$-quark mass terms can indeed provide sizable contributions. Furthermore, based on the newly obtained moments, a model for the kaon twist-3 wavefunction $Ψ_{p,σ}^K(x,\mathbf{k}_\perp)$ with a better end-point behavior is constructed, which shall be useful for perturbative QCD calculations. As a byproduct, we make a discussion on the properties of the pion twist-3 DAs.

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arXiv2011

Hadronic Production of the Doubly Heavy Baryon $Ξ_{bc}$ at LHC

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.

hep-ph↗

arXiv2011

New results on Pionic Twist-3 Distribution Amplitudes within the QCD Sum Rules

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.

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arXiv2009

Hadronic production of $B^{(*)}_s$ at TEVATRON and LHC

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.

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