"table_signalregion_cat2_postfit" of "Inclusive and differential cross section measurements of single top quark production in association with a Z boson in proton-proton collisions at $\sqrt{s}$ = 13 TeV"

Inclusive and differential cross sections of single top quark production in association with a Z boson are measured in proton-proton collisions at a center-of-mass energy of 13 TeV with an integrated luminosity of $138\ \mathrm{fb}^{-1}$ recorded by the CMS experiment. Events are selected based on the presence of three leptons, electrons or muons, associated with leptonic Z boson and top quark decays. The measurement yields an inclusive cross section of $87.9\text{ }_{-7.3}^{+7.5}\text{ (stat) }_{-6.0}^{+7.3}\text{ (syst) fb}$ for a dilepton invariant mass greater than 30 GeV, in agreement with standard model (SM) calculations. The ratio between the cross sections for the top quark and the top antiquark production in association with a Z boson is measured as $2.37\text{ }_{-0.42}^{+0.56}\text{ (stat) }_{-0.13}^{+0.27}\text{ (syst)}$. Differential measurements at parton and particle levels are performed for the first time. Several kinematic observables are considered to study the modeling of the process. Results are compared to theoretical predictions with different assumptions on the source of the initial-state b quark and found to be in agreement, within the uncertainties. Additionally, the spin asymmetry, which is sensitive to the top quark polarization, is determined from the differential distribution of the polarization angle at parton level to be $0.58\text{ }^{+0.15}_{-0.16} \text{ (stat) } {\pm 0.06}\text{ (syst)}$, in agreement with SM predictions using the MGvATNLO event generator at next-to-leading order.

本研究利用CMS实验（CMS）采集的质心系能量为13 TeV、积分亮度138 fb⁻¹的质子-质子（proton-proton）对撞数据，测量了伴随Z玻色子（Z boson）的单顶夸克（top quark）产生过程的总截面与微分截面。事件筛选标准基于三个轻子（lepton）——电子（electron）或缪子（muon）——的存在，这些轻子对应Z玻色子与顶夸克的轻子型衰变。在双轻子不变质量（dilepton invariant mass）大于30 GeV的条件下，本次测量得到的总截面为87.9 +7.5(统计)−7.3 +7.3(系统)−6.0 fb，与标准模型（Standard Model, SM）的理论计算结果一致。本研究还测定了伴随Z玻色子产生的顶夸克与反顶夸克（top antiquark）的截面比值，结果为2.37 +0.56(统计)−0.42 +0.27(系统)−0.13。本研究首次开展了部分子层次（parton level）与粒子层次（particle level）的微分截面测量。研究选取了多个运动学可观测量（kinematic observable），用于分析该过程的理论建模方案。将测量结果与针对初始态b夸克（initial-state b quark）来源采用不同假设的理论预言进行对比，结果在不确定度范围内与理论预言相符。此外，本研究通过部分子层次下极化角（polarization angle）的微分分布，测定了对顶夸克极化（top quark polarization）敏感的自旋不对称度（spin asymmetry）为0.58 +0.15(统计)−0.16 ±0.06(系统)，与采用MGvATNLO事件产生器（event generator）在次领头阶（next-to-leading order, NLO）下得到的标准模型预言一致。