Pion Electromagnetic Form Factor in the $K_T$ Factorization Formulae

Abstract

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 $F_{\pi }(Q^2)$ are recalculated. In particular, the contribution to the pion form factor from the higher helicity components (${\lambda }_1+{\lambda }_2=\pm 1$), 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 ${\psi }_p(x,{\mathbf{k}}_{\perp })$ 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 (${\lambda }_1+{\lambda }_2=0$) and the higher helicity components (${\lambda }_1+{\lambda }_2=\pm 1$) 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 $Q^2\sim 10Ge{V}^2$. 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 ${\alpha }_s$, 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.

4 pages, 2 figures, Prepared for International Conference on QCD and Hadronic Physics, Beijing, China, 16-20 June 2005

References in corpus (2)

• A Model for the Twist-3 Wave Function of the Pion and Its Contribution to the Pion Form Factor
• Pion Form Factor in the $k_T$ Factorization Formalism

Cited by in corpus (16)

• An Implication on the Pion Distribution Amplitude from the Pion-Photon Transition Form Factor with the New BABAR Data
• Constraints on the Light Pseudoscalar Meson Distribution Amplitudes from Their Meson-Photon Transition Form Factors
• An improved light-cone harmonic oscillator model for the pionic leading-twist distribution amplitude
• Determination of the pion distribution amplitude
• A Comprehensive Analysis on the Pion-Photon Transition Form Factor Beyond the Leading Fock State
• $B\to K$ Transition Form Factor up to $\mathcal{O}(1/m_b^2)$ within the $k_T$ Factorization Approach
• Heavy and light meson wavefunctions
• Information on the Pion Distribution Amplitude from the Pion-Photon Transition Form Factor with the Belle and BaBar Data
• $B\to \rho$ transition form factors within the QCD light-cone sum rules and the $\rho$-meson leading-twist distribution amplitude
• $K_0^{\ast }(1430)$ Twist-2 Distribution Amplitude and $B_s,D_s\to K_0^{\ast }(1430)$ Transition Form Factors
• $V_{cb}$ from the semileptonic decay $B\to D\ell {\bar{\nu }}_{\ell }$ and the properties of the $D$ meson distribution amplitude
• $a_0(980)$-meson twist-2 distribution amplitude within the QCD sum rules and investigation of $D\to a_0(980)(\to \eta \pi )e^{+}{\nu }_e$
• Kaon Electromagnetic Form Factor within the $k_T$ Factorization Formalism and It's Light-Cone Wave Function
• Footprint in fitting $B\to D$ vector form factor and determination for $D$-meson leading-twist LCDA
• $\gamma \gamma \to M^{+}{M}^{-}(M=\pi ,K)$ processes with twist-3 corrections in QCD
• Status of the $D_s^{+}\to \varphi {\ell }^{+}{\nu }_{\ell }$ decay with a chiral-odd $\varphi$-meson light-cone distribution amplitude