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arXiv 2005.05978hep-phhep-exhep-lat
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标准模型中的$\varepsilon'/\varepsilon$在2020年代初

$\varepsilon'/\varepsilon$ in the Standard Model at the Dawn of the 2020s

Jason Aebischer, Christoph Bobeth, Andrzej J. Buras

摘要:

我们重新分析比例$\varepsilon'/\varepsilon$在标准模型(SM)使用最新的强子矩阵元素从RBC-UKQCD合作,结合最重要的NNLO QCD的修正,以电弱企鹅的贡献和同位旋破缺的修正。我们说明了后者的重要性,通过使用他们的最新估计手征微扰理论(ChPT)的基础上$octet$近似最低层的介子和最近的估计在$nonet$计划,考虑到$η_0$的贡献。我们分别找到了$(\varepsilon'/\varepsilon)^{(8)}_\text{SM} = (17.4 \pm 6.1) \times 10^{-4}$和$(\varepsilon'/\varepsilon)^{(9)}_\text{SM} = (13.9 \pm 5.2) \times 10^{-4}$。尽管与测量值$(\varepsilon'/\varepsilon)_\text{exp} = (16.6 \pm 2.3) \times 10^{-4}$非常一致,但$(\varepsilon'/\varepsilon)_\text{SM}$中的大误差仍然为该比率的重要新物理学(BSM)贡献留下了空间。我们更新了$(\varepsilon'/\varepsilon)_\text{BSM}$的2018年主公式,该公式适用于SM以外的任何扩展,无需额外的光自由度。我们在RBC-UKQCD协作使用的$μ$尺度和ChPT和DQCD使用的较低尺度$\mathcal{O}(1\,\text{GeV})$上提供了企鹅参数$B_6^{(1/2)}(μ)$和$B_8^{(3/2)}(μ)$的新值。我们提出了半解析公式$(\varepsilon'/\varepsilon)_\text{SM}$在这些参数和$\hatΩ_\text{eff}$,总结了这个比例的同位旋破修正。我们强调的重要性,晶格计算的$\mathcal{O}(α_\text{em})$贡献的强子矩阵元素的必要的$\mathcal{O}(α_\text{em})$在$\varepsilon'/\varepsilon$目前的分析中的重整化方案的依赖。

英文摘要:

We reanalyse the ratio $\varepsilon'/\varepsilon$ in the Standard Model (SM) using most recent hadronic matrix elements from the RBC-UKQCD collaboration in combination with most important NNLO QCD corrections to electroweak penguin contributions and the isospin-breaking corrections. We illustrate the importance of the latter by using their latest estimate from chiral perturbation theory (ChPT) based on the $octet$ approximation for lowest-lying mesons and a very recent estimate in the $nonet$ scheme that takes into account the contribution of $η_0$. We find $(\varepsilon'/\varepsilon)^{(8)}_\text{SM} = (17.4 \pm 6.1) \times 10^{-4}$ and $(\varepsilon'/\varepsilon)^{(9)}_\text{SM} = (13.9 \pm 5.2) \times 10^{-4}$, respectively. Despite a very good agreement with the measured value $(\varepsilon'/\varepsilon)_\text{exp} = (16.6 \pm 2.3) \times 10^{-4}$, the large error in $(\varepsilon'/\varepsilon)_\text{SM}$ still leaves room for significant new physics (BSM) contributions to this ratio. We update the 2018 master formula for $(\varepsilon'/\varepsilon)_\text{BSM}$ valid in any extension beyond the SM without additional light degrees of freedom. We provide new values of the penguin parameters $B_6^{(1/2)}(μ)$ and $B_8^{(3/2)}(μ)$ at the $μ$-scales used by the RBC-UKQCD collaboration and at lower scales $\mathcal{O}(1\,\text{GeV})$ used by ChPT and DQCD. We present semi-analytic formulae for $(\varepsilon'/\varepsilon)_\text{SM}$ in terms of these parameters and $\hatΩ_\text{eff}$ that summarizes isospin-breaking corrections to this ratio. We stress the importance of lattice calculations of the $\mathcal{O}(α_\text{em})$ contributions to the hadronic matrix elements necessary for the removal of renormalization scheme dependence at $\mathcal{O}(α_\text{em})$ in the present analyses of $\varepsilon'/\varepsilon$.

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