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arXiv 1807.02121hep-phhep-ex
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在未来轻子对撞机上顶夸克有效场论的整体和最佳探测

Global and optimal probes for the top-quark effective field theory at future lepton colliders

Gauthier Durieux, Martín Perelló, Marcel Vos, Cen Zhang

摘要:

我们研究了在未来的轻子对撞机上精确测量顶夸克对的标准模型之外的物理敏感性。一个全球性的有效场论方法,包括华沙基础,涉及顶夸克和产生树级振幅,干扰标准模型$e^+e^-\to t\,\bar t\to bW^+\bar bW^-$的极限消失$b$夸克质量的所有维度6运营商。四费米子和CP破坏的贡献被考虑在内。圆形对撞机,ILC和CLIC类基准运行的情况进行了检查。我们比较了各种观测的约束力的一组统计最优的,最大限度地利用全差分$bW^+\bar bW^-$分布中包含的信息。六维算子的线性贡献所获得的增强的灵敏度导致对二次算子不敏感的界限。即使是统计上最优的观测量,也需要两个质心能量来同时约束两个和四个费米子算子。讨论了质心能量杠杆臂的影响,以及光束偏振的影响。对类似ILC和CLIC的操作方案中所能达到的精确度进行现实的估计,可以得到顶夸克电弱耦合的个别限制,这些限制比Tevatron和LHC运行I数据的限制好一到三个数量级,比LHC高光度阶段最乐观的预测好三到两百倍。干净的全球约束,而且可以得到轻子对撞机,鲁棒地覆盖多维有效场论空间与极小模型的依赖。

英文摘要:

We study the sensitivity to physics beyond the standard model of precise top-quark pair production measurements at future lepton colliders. A global effective-field-theory approach is employed, including all dimension-six operators of the Warsaw basis which involve a top-quark and give rise to tree-level amplitudes that interfere with standard-model $e^+e^-\to t\,\bar t\to bW^+\bar bW^-$ ones in the limit of vanishing $b$-quark mass. Four-fermion and CP-violating contributions are taken into account. Circular-collider-, ILC- and CLIC-like benchmark run scenarios are examined. We compare the constraining power of various observables to a set of statistically optimal ones which maximally exploit the information contained in the fully differential $bW^+\bar bW^-$ distribution. The enhanced sensitivity gained on the linear contributions of dimension-six operators leads to bounds that are insensitive to quadratic ones. Even with statistically optimal observables, two centre-of-mass energies are required for constraining simultaneously two- and four-fermion operators. The impact of the centre-of-mass energy lever arm is discussed, that of beam polarization as well. A realistic estimate of the precision that can be achieved in ILC- and CLIC-like operating scenarios yields individual limits on the electroweak couplings of the top quark that are one to three orders of magnitude better than constraints set with Tevatron and LHC run I data, and three to two hundred times better than the most optimistic projections made for the high-luminosity phase of the LHC. Clean global constraints can moreover be obtained at lepton colliders, robustly covering the multidimensional effective-field-theory space with minimal model dependence.

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