arXiv 1602.035602016-02hep-lathep-ph

$B^0_{(s)}$ -从格点量子色动力学中得到的混合矩阵元用于标准模型及更高

$B^0_{(s)}$-mixing matrix elements from lattice QCD for the Standard Model and beyond

A. Bazavov, C. Bernard, C. M. Bouchard, C. C. Chang, C. DeTar, Daping Du, A. X. El-Khadra, E. D. Freeland, E. Gamiz, Steven Gottlieb, U. M. Heller, A. S. Kronfe… 展开作者

A. Bazavov, C. Bernard, C. M. Bouchard, C. C. Chang, C. DeTar, Daping Du, A. X. El-Khadra, E. D. Freeland, E. Gamiz, Steven Gottlieb, U. M. Heller, A. S. Kronfeld, J. Laiho, P. B. Mackenzie, E. T. Neil, J. Simone, R. Sugar, D. Toussaint, R. S. Van de Water, Ran Zhou

备注：: 75 pp, 17 figs. Ver 2 fixes typos; corrects mistakes resulting in slight changes to results, correlation matrices; updates decay constants to agree with recent PDG update; corrects uncertainties for tree-level CKM matrix elements used in comparison, slightly reducing tensions; includes additional analyses that support mostly-nonperturbative matching; expands discussion of isospin-breaking effects
发表信息：: Phys. Rev. D 93, 113016 (2016)
DOI：: 10.1103/PhysRevD.93.113016

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摘要：

本文首次在三味格点量子色动力学中计算了在标准模型内和标准模型外对中性$B^0$ -和$B_s$ -介子混合有贡献的所有五个定域算符的强子矩阵元。我们提出了一个完整的误差预算为每个矩阵元素，也提供了完整的矩阵元素之间的相关性。我们还提出了相应的袋参数和它们的相关性，以及特定的混合矩阵元素的组合，进入中性$B$介子宽度差的表达式。我们得到了迄今为止SU（3）破缺比$ξ= 1.206(18)(6)$的最精确的测定，其中第二个误差来自于忽略了粲海夸克，而第一个误差包含了所有其他的不确定性。相对于2013年Flavor Lattice Averaging Group结果，总不确定性降低了三倍，收紧了$B$混合对Cabibbo-Kobayashi-Maskawa（CKM）幺正三角形的约束。我们的计算采用规范场合奏产生的MILC合作与四个晶格间距和π介子质量接近的物理值。我们对轻价夸克采用asqtad改进的交错作用量，对底夸克采用费米实验室方法。我们使用重轻介子手征微扰理论修正，包括晶格间距的影响外推的五个矩阵元素的物理点。我们结合我们的结果与中性$B$介子振荡频率的实验测量，以确定CKM矩阵元$|V_{td}| = 8.00(34)(8) \times 10^{-3}$，$|V_{ts}| = 39.0(1.2)(0.4) \times 10^{-3}$，和$|V_{td}/V_{ts}| = 0.2052(31)(10)$，这不同于CKM幺正性预期约2 $σ$。这些结果和其他来自口味变化中性电流的结果表明，在环路和树水平上介导的弱过程之间存在一种新的紧张关系。

英文摘要：

We calculate---for the first time in three-flavor lattice QCD---the hadronic matrix elements of all five local operators that contribute to neutral $B^0$- and $B_s$-meson mixing in and beyond the Standard Model. We present a complete error budget for each matrix element and also provide the full set of correlations among the matrix elements. We also present the corresponding bag parameters and their correlations, as well as specific combinations of the mixing matrix elements that enter the expression for the neutral $B$-meson width difference. We obtain the most precise determination to date of the SU(3)-breaking ratio $ξ= 1.206(18)(6)$, where the second error stems from the omission of charm sea quarks, while the first encompasses all other uncertainties. The threefold reduction in total uncertainty, relative to the 2013 Flavor Lattice Averaging Group results, tightens the constraint from $B$ mixing on the Cabibbo-Kobayashi-Maskawa (CKM) unitarity triangle. Our calculation employs gauge-field ensembles generated by the MILC Collaboration with four lattice spacings and pion masses close to the physical value. We use the asqtad-improved staggered action for the light valence quarks, and the Fermilab method for the bottom quark. We use heavy-light meson chiral perturbation theory modified to include lattice-spacing effects to extrapolate the five matrix elements to the physical point. We combine our results with experimental measurements of the neutral $B$-meson oscillation frequencies to determine the CKM matrix elements $|V_{td}| = 8.00(34)(8) \times 10^{-3}$, $|V_{ts}| = 39.0(1.2)(0.4) \times 10^{-3}$, and $|V_{td}/V_{ts}| = 0.2052(31)(10)$, which differ from CKM-unitarity expectations by about 2$σ$. These results and others from flavor-changing-neutral currents point towards an emerging tension between weak processes that are mediated at the loop and tree levels.

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