"particle_abs_ZPt_covariance_stat" 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.

CMS实验利用质心系能量13 TeV、积分亮度138 fb⁻¹的质子-质子碰撞采集数据，测量了伴随Z玻色子产生的单顶夸克过程的总截面与微分截面。实验通过轻子衰变型Z玻色子与顶夸克衰变产生的3个轻子（电子或μ子）信号筛选事件。当双轻子不变质量大于30 GeV时，测得总截面为$87.9^{+7.5}_{-7.3} ext{（统计）}^{+7.3}_{-6.0} ext{（系统） fb}$，与标准模型（Standard Model, SM）的理论计算结果一致。同时测得伴随Z玻色子产生的顶夸克与反顶夸克的产生截面之比为$2.37^{+0.56}_{-0.42} ext{（统计）}^{+0.27}_{-0.13} ext{（系统）}$。本研究首次在部分子层级与粒子层级开展了该过程的微分截面测量。选取多个运动学可观测量以研究该过程的理论建模。将实验结果与针对初始态b夸克来源采用不同假设的理论预言进行对比，发现在不确定度范围内两者结果一致。此外，通过部分子层级极化角的微分分布，测得对顶夸克极化敏感的自旋不对称度为$0.58^{+0.15}_{-0.16} ext{（统计）} pm 0.06 ext{（系统）}$，与采用MGvATNLO事件发生器在次领头阶（next-to-leading order, NLO）下的标准模型预言相符。