光子-π介子跃迁形状因子：BABAR难题被破解
Photon-pion transition form factor: BABAR puzzle is cracked
摘要：
最近，BABAR合作组公布了（arXiv：0905.4778）光子-π介子跃迁形状因子$F_{πγγ^{\ast}}(Q^{2})$的数据，这与微扰QCD的标准因子分解方法的预测是强烈矛盾的。紧接着，提出了两种机制（A.E. Dorokhov，arXiv：0905.4577; A. V. Radyushkin，arXiv：0906.0323），其在数学上增强了形状因子渐近性，因此提供了对BABAR数据的定性满意描述。然而，巴巴尔效应的物理学原理并没有完全阐明。在目前的工作中，基于对QCD真空的非微扰方法和相当普遍的假设，我们证明了π介子跃迁形状因子存在两个渐近区域。一个具有渐近性$F_{πγ^{\ast}γ}(Q^{2})\sim1/Q^{2}$的区域对应于标准QCD因子分解方法的结果，而另一个区域违反标准因子分解并导致渐近行为为$F_{πγ^{\ast}γ}(Q^{2})\sim\ln(Q^{2})Q^{2}$。此外，考虑特定的非定域手征夸克模型，我们找到了参数区域，在该区域成功描述了现有的π介子跃迁形状因子的CELLO、CLEO和BABAR数据。
英文摘要：
Recently, the BABAR collaboration published (arXiv:0905.4778) data for the photon-pion transition form factor $F_{πγγ^{\ast}}(Q^{2})$, which are in strong contradiction to the predictions of the standard factorization approach to perturbative QCD. Immediately afterwards, two mechanisms were suggested (A.E. Dorokhov, arXiv:0905.4577; A.V. Radyushkin, arXiv:0906.0323), that logarithmically enhance the form factor asymptotics and therefore provide a qualitatively satisfactory description of the BABAR data. However, the physics of the BABAR effect was not fully clarified. In the present work, based on a nonperturbative approach to the QCD vacuum and on rather universal assumptions, we show that there exists two asymptotic regimes for the pion transition form factor. One regime with asymptotics $F_{πγ^{\ast}γ}(Q^{2})\sim1/Q^{2}$ corresponds to the result of the standard QCD factorization approach, while other violates the standard factorization and leads to asymptotic behavior as $F_{πγ^{\ast}γ}(Q^{2})\sim\ln(Q^{2})Q^{2}$. Furthermore, considering specific nonlocal chiral quark models, we find the region of parameters, where the existing CELLO, CLEO and BABAR data for the pion transition form factor are successfully described.
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