Bai Ziyuan, Christ Norman H, Feng Xu, Lawson Andrew, Portelli Antonin, Sachrajda Christopher T
Physics Department, Columbia University, New York, New York 10027, USA.
School of Physics, Peking University, Beijing 100871, China and Collaborative Innovation Center of Quantum Matter, Beijing 100871, China and Center for High Energy Physics, Peking University, Beijing 100871, China and Physics Department, Columbia University, New York, New York 10027, USA.
Phys Rev Lett. 2017 Jun 23;118(25):252001. doi: 10.1103/PhysRevLett.118.252001. Epub 2017 Jun 21.
We report a first, complete lattice QCD calculation of the long-distance contribution to the K^{+}→π^{+}νν[over ¯] decay within the standard model. This is a second-order weak process involving two four-Fermi operators that is highly sensitive to new physics and being studied by the NA62 experiment at CERN. While much of this decay comes from perturbative, short-distance physics, there is a long-distance part, perhaps as large as the planned experimental error, which involves nonperturbative phenomena. The calculation presented here, with unphysical quark masses, demonstrates that this contribution can be computed using lattice methods by overcoming three technical difficulties: (i) a short-distance divergence that results when the two weak operators approach each other, (ii) exponentially growing, unphysical terms that appear in Euclidean, second-order perturbation theory, and (iii) potentially large finite-volume effects. A follow-on calculation with physical quark masses and controlled systematic errors will be possible with the next generation of computers.
我们报告了在标准模型内对(K^{+}→π^{+}νν[\overline{]})衰变的长程贡献进行的首次完整格点量子色动力学计算。这是一个涉及两个四费米子算符的二阶弱过程，对新物理高度敏感，欧洲核子研究中心的NA62实验正在对其进行研究。虽然这种衰变的大部分来自微扰的短程物理，但存在一个长程部分，可能与计划的实验误差一样大，这涉及非微扰现象。这里给出的使用非物理夸克质量的计算表明，通过克服三个技术难题，可以用格点方法计算这一贡献：（i）当两个弱算符相互靠近时出现的短程发散；（ii）在欧几里得二阶微扰理论中出现的指数增长的非物理项；（iii）潜在的大有限体积效应。使用下一代计算机将有可能进行具有物理夸克质量和可控系统误差的后续计算。
