We study the $ρπ$ and $b_1π$ decay modes of the $1^{-+}$ light hybrid state within the framework of light-cone QCD sum rules. We use both the tensor current $\barψσ_{μν}ψ$ and the derivative current $\barψ\overleftrightarrow{D}_μγ_5ψ$ as interpolating currents to calculate the partial decay width of the $b_1π$ decay mode. Comparing the sum rules obtained by using different currents, we obtain $Γ(π_1\to b_1π)$ = 8--23, 32--86 and 52--151\,MeV for $m_{1^{-+}}$ = 1.6, 1.8 and 2.0\,GeV respectively, which favour the results from the flux tube models and lattice simulations. We also use the tensor current to study the $ρπ$ decay mode, and although an extended stability criterion is needed, our results suggest a small partial decay width.
We make a detailed study on the typical production channel of double charmoniums, $e^+e^-\to J/ψ+η_c$, at the center-of-mass collision energy $\sqrt{s}=10.58$ GeV. The key component of the process is the form factor $F_{\rm VP}(q^2)$, which has been calculated within the QCD light-cone sum rules (LCSR). To improve the accuracy of the derived LCSR, we keep the $J/ψ$ light-cone distribution amplitude up to twist-4 accuracy. Total cross sections for $e^+e^-\to J/ψ+η_c$ at three typical factorization scales are $σ|_{μ_s} = 22.53^{+3.46}_{-3.49}~{\rm fb}$, $σ|_{μ_k} = 21.98^{+3.35}_{-3.38}~{\rm fb}…
We discuss the equivalence between light-front time-ordered-perturbation theory and covariant quantum field theory in light-front quantization, in the case of quantum electrodynamics at one-loop level. In particular, we review the one-loop calculation of the vertex correction, fermion self-energy and vacuum polarization. We apply the procedure of integration by residue over the light-front energy in the loop to show how the perturbative expansion in covariant terms can be reduced to a sum of propagating and instantaneous diagrams of light-front time-ordered perturbation theory. The detailed pr…
We extract the light-cone wavefunctions of the rho meson using the HERA data on diffractive rho photoproduction. We find good agreement with predictions for the distribution amplitude based on QCD sum rules and from the lattice. We also find that the data prefer a transverse wavefunction with enhanced end-point contributions.
We describe a consistent approach to factorization of scattering amplitudes for exclusive processes beyond the leading twist approximation. The method involves the Taylor expansion of the scattering amplitude in the momentum space around the dominant light-cone direction and thus naturally introduces an appropriate set of non-perturbative correlators which encode effects not only of the lowest but also of the higher Fock states of the produced particle. The reduction of original set of correlators to a set of independent ones is achieved with the help of equations of motion and invariance of t…
Exclusive processes in hard electroproduction is one of the best place for understanding the factorization properties of QCD. The HERA experiment recently provided precise data for rho electroproduction, including all spin density matrix elements. From QCD, it is expected that such a process should factorize between a hard (calculable) coefficient function, and hadronic (p and rho) matrix elements. Such a factorization is up to now only proven for a longitudinaly polarized rho. Within the kt-factorization approach (valid at large s_{gamma* p}), we evaluate the impact factor of the transition g…
The approximate tree decays B- -> pi- pi0/rho- rho0 may serve as benchmark channels for testing the various theoretical descriptions of the strong interaction dynamics in hadronic B meson decays. The ratios of hadronic and differential semileptonic B -> pi l nu/rho l nu decay rates at maximum recoil provide particularly clean probes of the QCD dynamics. We confront the recent NNLO calculation in the QCD factorization framework with experimental data and find support for the factorization assumption. A detailed analysis of all tree-dominated B -> pi pi/pi rho/rho rho decay modes seems to favour…
Exclusive processes in hard electroproduction are one of the best place for understanding QCD in view of its factorization properties. In particular, in the limit of asymptotic gamma* p center of mass energy, they give an access to the perturbative Regge properties of QCD. The HERA experiment recently provided precise data for rho electroproduction, including all spin density matrix elements. From QCD, it is expected that such a process should factorize between a hard (calculable) coefficient function, and hadronic (p and rho) matrix elements. Such a factorization is up to now only proven for …
Lepton flavour universality (LFU) in B-decays is revisited by considering a class of semileptonic operators defined at a scale Lambda above the electroweak scale v. The importance of quantum effects, so far neglected in the literature, is emphasised. We construct the low-energy effective Lagrangian taking into account the running effects from Lambda down to v through the one-loop renormalization group equations (RGE) in the limit of exact electroweak symmetry and QED RGEs from v down to the 1 GeV scale. The most important quantum effects turn out to be the modification of the leptonic coupling…
We calculate the gravitational form factors of the pion, sigma meson, and rho meson in the Nambu-Jona-Lasinio (NJL) model of quantum chromodynamics. The canonical energy-momentum tensor (EMT) is used in their derivation, allowing the possibility of an antisymmetric contribution when the hadron has intrinsic spin. We show that the asymmetric graviton vertex arising from the canonical EMT satisfies a simpler Ward-Takahashi identity (WTI) than the symmetric graviton vertex of the Belinfante EMT. The necessity of fully dressing the graviton vertex through the relevant Bethe-Salpeter equation is de…
Spectator interactions in B -> V gamma decays and QCD factorisation
我们在QCD因子分解的框架下研究了辐射衰变B -> V γ（其中V=rho，K^*），特别是硬旁观者对衰变振幅的贡献。对于显着的色磁运营商，我们显示了一个明确的下一个领先的顺序计算，观众的相互作用因式分解的重夸克极限，即它们可以被写为卷积的硬散射内核，微扰理论计算，和光锥分布振幅的B和V介子，其中包含软物理。一个sqrt{Lambda_QCD M_B}阶的中间尺度的存在导致了Sudakov谱的存在。我们表明如何证明因式分解可以扩展到其他（四夸克）运营商。
Snapshots of Hadrons, or the Story of How the Vacuum Medium Determines the Properties of the Classical Mesons Which Are Produced, Live and Die in the QCD Vacuum
We discuss exclusive radiative decays in QCD factorization within the Standard Model. In particular, we consider the decays B -> V gamma, with a vector meson K* or rho in the final state, and the double radiative modes B_s -> gamma gamma and B_d -> gamma gamma. At quark level, all these decays are governed by the flavour-changing neutral-current b -> s gamma or b -> d gamma transitions, which appear at the one-loop level in the Standard Model. Such processes allow us to study CP violation and the interplay of strong and electroweak interactions, to determine parameters of the CKM matrix, and t…
In the case of heavy-to-light weak meson transitions, a Quark Model derivation leads to very general relations between the form factors that parametrize the hadronic matrix elements. We investigate to what extent these form factor relations remain a good approximation, beyond the Quark Model. In heavy-to-light pseudoscalar-to-vector meson transitions, a simple argument shows that the V-A structure of the weak interaction leads to a strong suppression of the helicity h=+1 amplitude - an effect that has been confirmed experimentally by the CLEO Collaboration, with a full angular analysis of the …
