A per-cent-level determination of the nucleon axial coupling from quantum chromodynamics
A per-cent-level determination of the nucleon axial coupling from quantum chromodynamics
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DOI：
10.1038/s41586-018-0161-8
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发表时间：
2018-05
期刊：
影响因子：
64.8
通讯作者：
Chia-Cheng Chang;A. Nicholson;E. Rinaldi;E. Berkowitz;N. Garron;D. Brantley;H. Monge-Camacho;C. Monahan;C. Bouchard;M. Clark;B. Joó;T. Kurth;K. Orginos;P. Vranas;A. Walker-Loud
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文献类型：
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作者：
Chia-Cheng Chang;A. Nicholson;E. Rinaldi;E. Berkowitz;N. Garron;D. Brantley;H. Monge-Camacho;C. Monahan;C. Bouchard;M. Clark;B. Joó;T. Kurth;K. Orginos;P. Vranas;A. Walker-Loud
核子的轴向耦合gA是它与粒子物理学标准模型的弱轴向电流的耦合强度，就像电荷是与电磁流的耦合强度一样。这种轴向耦合决定了中子衰变为质子的速率、核子之间长程引力的强度以及核物理的其他特征。在核环境中对标准模型的精确测试需要对核物理学有定量的理解，而这一理解植根于标准模型的支柱--量子色动力学。的重要性gA使它成为一个基准量，以确定理论上的一项艰巨的任务，因为量子色动力学是非微扰，排除已知的分析方法。晶格量子色动力学提供了可以数值实现的量子色动力学的严格、非微扰定义。据估计，如果克服两个挑战，到2020年，2%的精度将是可能的：在计算中必须控制来自激发态的gA污染，统计精度必须显著提高。在这里，我们使用一种非传统的方法，灵感来自费曼-赫尔曼定理，克服了这些挑战。我们计算出agA值为1.271 ± 0.013，其精度约为1%。
The axial coupling of the nucleon,gA, is the strength of its coupling to the weak axial current of the standard model of particle physics, in much the same way as the electric charge is the strength of the coupling to the electromagnetic current. This axial coupling dictates the rate at which neutrons decay to protons, the strength of the attractive long-range force between nucleons and other features of nuclear physics. Precision tests of the standard model in nuclear environments require a quantitative understanding of nuclear physics that is rooted in quantum chromodynamics, a pillar of the standard model. The importance ofgAmakes it a benchmark quantity to determine theoretically—a difficult task because quantum chromodynamics is non-perturbative, precluding known analytical methods. Lattice quantum chromodynamics provides a rigorous, non-perturbative definition of quantum chromodynamics that can be implemented numerically. It has been estimated that a precision of two per cent would be possible by 2020 if two challenges are overcome,: contamination ofgAfrom excited states must be controlled in the calculations and statistical precision must be improved markedly, , , , , , , –. Here we use an unconventional method inspired by the Feynman–Hellmann theorem that overcomes these challenges. We calculate agAvalue of 1.271 ± 0.013, which has a precision of about one per cent.