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arXiv 1903.07570hep-ex
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用ATLAS探测器中的$pp$测量$\sqrt{s} = 13$ TeV的$eμ$通道中顶夸克对自旋相关

Measurements of top-quark pair spin correlations in the $eμ$ channel at $\sqrt{s} = 13$ TeV using $pp$ collisions in the ATLAS detector

ATLAS Collaboration

摘要:

利用大型强子对撞机ATLAS探测器记录的36.1 fb $^{-1}$的$\sqrt{s} = 13$ TeV的$pp$碰撞数据,测量了$t\bar{t}$产生过程中对自旋关联敏感的观测量.微分截面测量事件正好一个电子和一个μ子与相反的符号电荷作为一个功能的方位角的开口角和绝对差异的赝快度之间的电子和μ子候选人在实验室框架。还测量了作为$t\bar{t}$系统不变质量的函数的方位角开度角。所测得的微分截面进行比较,由几个非线性光学蒙特卡罗发电机和固定阶计算的预测。所观察到的自旋相关程度略高于所用发生器的预测。这些数据与NLO的一个固定阶计算的预测一致,但与高阶预测不太一致。利用这些轻子观测量,进行搜索对生产的超对称顶方衰变成标准模型顶夸克和轻中性伴。顶夸克质量之间的170和230 GeV的主要排除在95%的置信水平的运动学允许的值的中性伴子质量。

英文摘要:

A measurement of observables sensitive to spin correlations in $t\bar{t}$ production is presented, using 36.1 fb$^{-1}$ of $pp$ collision data at $\sqrt{s} = 13$ TeV recorded with the ATLAS detector at the Large Hadron Collider. Differential cross-sections are measured in events with exactly one electron and one muon with opposite-sign electric charge as a function of the azimuthal opening angle and the absolute difference in pseudorapidity between the electron and muon candidates in the laboratory frame. The azimuthal opening angle is also measured as a function of the invariant mass of the $t\bar{t}$ system. The measured differential cross-sections are compared to predictions by several NLO Monte Carlo generators and fixed-order calculations. The observed degree of spin correlation is somewhat higher than predicted by the generators used. The data are consistent with the prediction of one of the fixed-order calculations at NLO, but agree less well with higher-order predictions. Using these leptonic observables, a search is performed for pair production of supersymmetric top squarks decaying into Standard Model top quarks and light neutralinos. Top squark masses between 170 and 230 GeV are largely excluded at the 95% confidence level for kinematically allowed values of the neutralino mass.

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