Finite-Width Correction to Form Factors of γγ^＊→ π^0 Transition

Instead of the usual zero-width approximation for one resonance, we use the finite-width approximation for the two low resonances, i.e. the ρ- ω mesons, to investigate the light-cone local QCD sum rules for the form factor of the transition γγ^＊→ π^0 ,According to the method of the analytic continuation by duality, the weight function, the polynomial of a low order N, is added to the dispersion integral to annihilate the integrand in the region where both resonance saturation and the QCD asymptotic expression are least reliable. The resultant form factor in the cases for the zero- and finite-widths are almost the same, both agree well with the experimental measurements. A comparison with the result from the Laplacian transformed light-cone sum rules and a brief discussion are given.     

γγ*→π0跃迁的形状因子对共振态谱有限宽度的依赖性

基于量子色动力学（QCD）定域光锥求和规则，用ρ-ω介子共振态有限宽度近似取代了通常的零宽度近似，采用对偶解析延拓（ACD）方法，在色散关系中取N阶多项式为权重函数来清除或削弱共振谱和量子色动力学中不可靠区域的积分的影响，通过分析计算得到了γγ^＊→π0形状因子Fγγ^＊→π0（0，Q^2）的解析式及其数值结果．结果表明由零宽度和有限宽度的共振谱形式得到的形状因子大致相同，且与实验数据符合，说明Fγγ^＊→π0（0，Q^2）对共振态谱宽度的大小仅有较弱的依赖性，并验证了π介子光锥波函数渐近形式的正确性．