论文标题
在$ \ sqrt {s} = 13 $ tev中产生的单个顶级夸克和古夸克的两极分化的测量
Measurement of the polarisation of single top quarks and antiquarks produced in the $t$-channel at $\sqrt{s}=13$ TeV and bounds on the $tWb$ dipole operator from the ATLAS experiment
论文作者
论文摘要
提出了同时测量$ t $ channel单顶Quark生产中顶级Quark和Top-Antiquark极化向量的三个组成部分。该分析基于来自Proton-Proton-Proton碰撞的数据，该中心能量为13 TEV，对应于139 fb $^{ - 1} $的综合发光度，并在LHC的Atlas检测器中收集。选定的事件完全包含一个孤立的电子或MUON，较大的缺少横向动量，正好是两个喷气机，一个是$ b $标记的。严格的选择要求用于区分背景贡献的$ t $ channel单顶夸克事件。从顶列列克顿电荷动量的方向余弦的分布中测量了顶夸克和顶部的极化向量。所选顶级事件样本的极化向量的三个组件是$ p_ {x'} = 0.01 \ pm0.18 $，$ p_ {y'} = -0.029 \ pm0.027 $，$ p_ {z'} -0.02 \ pm0.20 $，$ p_ {y'} = -0.007 \ pm0.051 $，$ p_ {z'} = -0.79 \ pm 0.16 $。在稳定颗粒水平上校正为基准区域的归一化差分横截面作为带电 - lepton角的函数，用于顶级Quark和Top-Antiquark事件。这些测量与标准模型预测一致。角度差异横截面用于在有效场理论的框架内，在尺寸六$ \ MATHCAL {o} _ {o} _ {o} _ {o} _ {o} _ {o} _ {o} _ {o} _ {o} _ {o}的复杂系数上得出边界。获得的界限为$ c_ {tw} \ in \ [-0.9,1.4] $和$ c_ {itw} \ in [-0.8,0.2] $，均为95 \％置信度。
A simultaneous measurement of the three components of the top-quark and top-antiquark polarisation vectors in $t$-channel single-top-quark production is presented. This analysis is based on data from proton--proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb$^{-1}$, collected with the ATLAS detector at the LHC. Selected events contain exactly one isolated electron or muon, large missing transverse momentum and exactly two jets, one being $b$-tagged. Stringent selection requirements are applied to discriminate $t$-channel single-top-quark events from the background contributions. The top-quark and top-antiquark polarisation vectors are measured from the distributions of the direction cosines of the charged-lepton momentum in the top-quark rest frame. The three components of the polarisation vector for the selected top-quark event sample are $P_{x'} =0.01\pm0.18$, $P_{y'} = -0.029\pm0.027$, $P_{z'} =0.91\pm0.10$ and for the top-antiquark event sample they are $P_{x'} = -0.02\pm0.20$, $P_{y'} = -0.007\pm0.051$, $P_{z'} = -0.79\pm 0.16$. Normalised differential cross-sections corrected to a fiducial region at the stable-particle level are presented as a function of the charged-lepton angles for top-quark and top-antiquark events inclusively and separately. These measurements are in agreement with Standard Model predictions. The angular differential cross-sections are used to derive bounds on the complex Wilson coefficient of the dimension-six $\mathcal{O}_{tW}$ operator in the framework of an effective field theory. The obtained bounds are $C_{tW} \in\ [-0.9,1.4]$ and $C_{itW} \in [-0.8,0.2]$, both at 95\% confidence level.
