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arXiv 1012.5634hep-phhep-ex
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矢量介子优势和π ^0跃迁形状因子

Vector meson dominance and the pi^0 transition form factor

Peter Lichard

摘要:

结果表明,π ^0跃迁形状因子F(Q_1^2,Q_2^2)与它的单实光子极限F(Q_1^2,0)有很大的不同,即使Q_2^2的值很小(约0.1 GeV^2),在实验中不能排除一个“未标记”的电子。它表明,数据与理论计算的比较,通常假设Q_2^2=0,可能是不可信的。我们的π ^0跃迁形状因子唯象模型是基于矢量介子占优假设,所有参数都是由矢量介子衰变的实验数据确定的。模型的可靠性在双实光子极限下进行了检验,在双实光子极限下,它提供了对π ^0-> 2伽马衰变率的良好的无参数描述,在π ^0 Dalitz衰变中也是如此。给出了在Q_2^2的几个固定值下F(Q_1^2,Q_2^2)对Q_1^2的依赖关系,并与已有的数据进行了比较。

英文摘要:

It is shown that the pi^0 transition form factor F(Q_1^2,Q_2^2) differs substantially from its one-real-photon limit F(Q_1^2,0) even for rather small values of Q_2^2 (approx 0.1 GeV^2), which cannot be excluded in experiments with one "untagged" electron. It indicates that the comparison of data with theoretical calculations, which usually assume Q_2^2=0, may be untrustworthy. Our phenomenological model of the pi^0 transition form factor is based on the vector-meson-dominance hypothesis and all its parameters are fixed by using the experimental data on the decays of vector mesons. The model soundness is checked in the two-real-photon limit, where it provides a good parameter-free description of the pi^0 -> 2 gamma decay rate, and in the pi^0 Dalitz decay. The dependence of F(Q_1^2,Q_2^2) on Q_1^2 at several fixed values of Q_2^2 is presented and the comparison with existing data performed.

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