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arXiv 1401.4099hep-phhep-ex
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共振手征理论中的VV 'P形状因子和pi-eta-eta'对μ介子g-2的逐光贡献

The VV'P form factors in resonance chiral theory and the pi-eta-eta' light-by-light contribution to the muon g-2

P. Roig, A. Guevara, G. López Castro

摘要:

对不同粒子虚度的VV 'P形状因子(V,V'代表矢量粒子,P代表赝标介子)的描述对强相互作用理论是一个挑战。虽然它们的手征极限已经被很好地理解,但最近在高光子虚度下对γ ^* omega pi ^0和γ ^* gamma pi ^0形状因子的测量似乎偏离了QCD提出的最简单的标度行为。在这里,我们试图描述他们在其整个测量的能量范围内的共振手性理论,一个框架,它自然地结合了手性限制的约束,并扩展到更高的能量,包括共振作为活跃的领域。具体来说,我们得到了一个准确的描述的数据高达2 GeV的前形状因子,包括三个多重态的矢量共振。即使在单共振近似下,与后者的测量结果也可能吻合得很好,尽管我们建议测量e^+e^-到mu^+mu^-pi ^0的截面和双μ子不变质量分布,以更好地表征这种形状因子。然后,我们计算了π交换对μ介子g-2的贡献,得到(6.66 \pm 0.21)× 10 ^{-10},并精确地确定了误差。我们还记得,用π介子极贡献近似整个π介子交换低估了异常的相应结果((15,20)%)。在此基础上,我们预测了eta^(\prime)跃迁的形状因子,得到了与实验数据很好的一致性,并得到了它们各自对μ子异常的贡献。这样,三个最轻的伪标量对它的贡献产生(10.47 \pm 0.54)x10^{-10},与以前的计算一致,但误差较小。

英文摘要:

The description of the VV'P form factors (V,V' stands for vector particles and P for a pseudoscalar meson) for different particles virtualities remains a challenge for the theory of strong interactions. While their chiral limit is well understood, recent measurements of the gamma^* omega pi^0 and gamma^* gamma pi^0 form factors at high photon virtualities seem to depart from the simplest scaling behavior suggested by QCD. Here we attempt to describe them in their whole measured energy regimes within the Resonance Chiral Theory, a framework which naturally incorporates the chiral limit constraints and extends to higher energies by including the resonances as active fields. Specifically, we obtained an accurate description of the data up to 2 GeV on the former form factor by including three multiplets of vector resonances. Good agreement with measurements of the latter was possible even in the single resonance approximation, although we propose to measure the e^+e^- to mu^+mu^-pi^0 cross-section and di-muon invariant mass distribution to better characterize this form factor. We have then evaluated the pion exchange contribution to the muon g-2 obtaining (6.66\pm0.21)x10^{-10} with an accurate determination of the errors. We have also recalled that approximating the whole pion exchange by the pion pole contribution underestimates the corresponding result for the anomaly (by (15,20)%). Based on these results, we have predicted the eta^(\prime) transition form factors obtaining good agreement with data and obtained their respective contributions to the muon anomaly. In this way, the contribution of the three lightest pseudoscalars to it yields (10.47\pm0.54)x10^{-10}, in agreement with previous evaluations but with smaller error.

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