论文标题

从锥形电磁形外偏式轻锥分布幅度

The pion light-cone distribution amplitude from the pion electromagnetic form factor

论文作者

Cheng, Shan, Khodjamirian, Alexander, Rusov, Aleksey V.

论文摘要

我们建议探测斜锥分布幅度,并在锥电磁形状效果上应用分散性关系。而不是标准色散关系,我们使用了空格般的外形元件$f_π(q^2)$与时态形式的集成模量之间的方程式。对于$f_π(q^2)$,使用具有主导扭曲2项的QCD轻单和规则。采用Pion Twist-2分布幅度的前几个Gegenbauer多项式的一定组合,可以使用该方程式拟合其系数$ a_ {2,4,6,...} $(Gegenbauer Moments),采用测量的Timelike TimeLike形式。对于探索性拟合,我们使用Babar协作的数据。结果绝对排除了渐近扭曲2分布幅度。同样,具有单个$ a_2 \ neq 0 $的模型也被拟合所散布。考虑到具有$ a_ {n> 2} \ neq 0 $的型号,我们发现第二和第四个gegenbauer矩的拟合值涵盖了$ a_2(1 \ mbox {gev})=(0.22-0.33)=(0.22-0.33)$,$ a_4($ a_4(1 \ mbox {GEV} {GEV} {0.25)=(0.25)。从$ a_ {8} $开始的较高的矩与零一致,尽管不确定性很大。从分散关系和轻单元规则中,以两种不同的方式获得的间距式触发形式,并在不确定性中同意了杰斐逊实验室$f_π$协作的测量。

We suggest to probe the pion light-cone distribution amplitude, applying a dispersion relation for the pion electromagnetic form factor. Instead of the standard dispersion relation, we use the equation between the spacelike form factor $F_π(Q^2)$ and the integrated modulus of the timelike form factor. For $F_π(Q^2)$, the QCD light-cone sum rule with a dominant twist-2 term is used. Adopting for the pion twist-2 distribution amplitude a certain combination of the first few Gegenbauer polynomials, it is possible to fit their coefficients $a_{2,4,6,...}$ (Gegenbauer moments) from this equation, employing the measured pion timelike form factor. For the exploratory fit we use the data of the BaBar collaboration. The results definitely exclude the asymptotic twist-2 distribution amplitude. Also the model with a single $a_2\neq 0$ is disfavoured by the fit. Considering the models with $a_{n>2}\neq 0$, we find that the fitted values of the second and fourth Gegenbauer moments cover the intervals $a_2 (1 \mbox{GeV}) = (0.22 - 0.33) $, $a_4 (1 \mbox{GeV}) = (0.12 - 0.25) $. The higher moments starting from $a_{8}$ are consistent with zero, albeit with large uncertainties. The spacelike pion form factor obtained in two different ways, from the dispersion relation and from the light-cone sum rule, agrees, within uncertainties, with the measurement by the Jefferson Lab $F_π$ collaboration.

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