长距离质子自旋结构的测量
Measurement of the proton spin structure at long distances
摘要：
测量质子和中子的自旋结构，检验我们对它们如何从夸克和胶子（核物质的基本组成部分）产生的理解。在长距离时，强相互作用的耦合常数会变大，需要非微扰方法来计算量子色动力学过程，例如格点规范理论或有效场论。在这里，我们报告质子自旋结构的测量散射极化电子束极化质子。自旋相关的横截面测量在大的距离，对应的区域之间的低动量转移平方0.012和1.0 GeV $^2$。这个运动学范围提供了独特的测试手征有效场论的预测。我们的结果表明，一个完整的描述核子自旋仍然难以捉摸，并要求进一步的理论工作，例如在晶格量子色动力学。最后，我们的数据外推到光子点同意Gerasimov-Drell-Hearn求和规则，这是量子场论的一个基本预测，它将质子的反常磁矩与其综合自旋相关截面联系起来。
英文摘要：
Measuring the spin structure of protons and neutrons tests our understanding of how they arise from quarks and gluons, the fundamental building blocks of nuclear matter. At long distances the coupling constant of the strong interaction becomes large, requiring non-perturbative methods to calculate quantum chromodynamics processes, such as lattice gauge theory or effective field theories. Here we report proton spin structure measurements from scattering a polarized electron beam off polarized protons. The spin-dependent cross-sections were measured at large distances, corresponding to the region of low momentum transfer squared between 0.012 and 1.0 GeV$^2$. This kinematic range provides unique tests of chiral effective field theory predictions. Our results show that a complete description of the nucleon spin remains elusive, and call for further theoretical works, e.g. in lattice quantum chromodynamics. Finally, our data extrapolated to the photon point agree with the Gerasimov-Drell-Hearn sum rule, a fundamental prediction of quantum field theory that relates the anomalous magnetic moment of the proton to its integrated spin-dependent cross-sections.
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