低Q^2条件下γ *p-> δ反应的测量：探测介子的贡献
Measurements of the gamma*p->Delta Reaction At Low Q^2: Probing the Mesonic Contribution
摘要：
在美因茨电子加速器（MAMI）上，通过δ区的$p(\vec{e},e'p)π^0$反应，以$Q^2=0.060$、0.127和0.200（GeV/c）^2的能量来测定长射程（低Q^{2}）核子的非球形角动量振幅，精确度为3%。主导过渡磁偶极子振幅和四极偶极比的结果已经获得了估计模型的不确定性，这是近似相同的实验不确定性。晶格和有效场论的预测同意我们的数据在相对较大的估计理论的不确定性。当共振振幅调整到数据时，唯象模型与实验符合得很好。为了检查反应模型计算，对低于共振的质心能量和$σ_{TL'}$结构函数进行了额外的数据。这些结果证实了在大距离下，π介子的贡献占主导地位，并具有普遍的Q^2变化。
英文摘要：
The determination of non-spherical angular momentum amplitudes in nucleons at long ranges (low Q^{2}), was accomplished through the $p(\vec{e},e'p)π^0$ reaction in the Delta region at $Q^2=0.060$, 0.127, and 0.200 (GeV/c)^2 at the Mainz Microtron (MAMI) with an accuracy of 3%. The results for the dominant transition magnetic dipole amplitude and the quadrupole to dipole ratios have been obtained with an estimated model uncertainty which is approximately the same as the experimental uncertainty. Lattice and effective field theory predictions agree with our data within the relatively large estimated theoretical uncertainties. Phenomenological models are in good agreement with experiment when the resonant amplitudes are adjusted to the data. To check reaction model calculations additional data were taken for center of mass energies below resonance and for the $σ_{TL'}$ structure function. These results confirm the dominance, and general Q^2 variation, of the pionic contribution at large distances.
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