论文标题
CMS实验中核核碰撞中最高夸克产生的证据
Evidence for top quark production in nucleus-nucleus collisions with the CMS experiment
论文作者
论文摘要
CMS实验在2018年记录的铅铅碰撞的数据样本中报告了在重离子碰撞中产生顶级夸克的证据$ 1.7 \ pm0.1 \，\ mathrm {nb}^{ - 1} $。顶级夸克对（$ \ mathrm {t \ bar {t}} $）的生产是在两个相对符号的高$ p_ \ mathrm {t} $隔离的leptons（$ \ ell^\ ell^\ ell^el^el^\ ell^\ mp = \，， \ Mathrm {e}^{ - }，\，μ^{+}μ^{ - }，\，\，\ Mathrm {and} \，\ Mathrm {e}^{\ pm}^{\ pm}μ^μ^{\ mp} $）。我们通过或不需要或不存在B标记的Jets的其他存在来测试对$ \ mathrm {t \ bar {t}} $信号过程的敏感性，因此证明了可行性可以识别顶级Quark Decay产品，无论与介质（底部Quarks）或不相互作用（leptontoical decay decay decay decay w bosons）。为此，包容性横截面（$σ_\ Mathrm {t \ bar {t}} $）是从可能性拟合到多变量鉴别器的，其中包括带有和不带有B-b-Tagged Jet Multiperity信息的不同Leptonic运动学变量。 $ \ mathrm {t \ bar {t}} $信号的观察到的（预期）意义分别为4.0（5.8）和3.8（4.8）标准偏差，对于带有B-jet多性输入的拟合和拟合。事件重建和背景减法后，提取的横截面为$σ_\ mathrm {t \ bar {t}} = 2.03 ^{+0.71} _ { - 0.64} $和$ 2.54 ^{+0.84} {+0.84} _ { - 0.74} _ { - 0.74} \，nisty nisty是$ { - { - 0.74} \，nisty nisty nisty是$ {与缩放质子 - 蛋白质数据以及扰动量子染色体动力学预测的期望兼容。该测量构成了使用顶级夸克作为探测强烈相互作用物质的新工具的关键步骤。
Evidence for the production of top quarks in heavy ion collisions is reported in a data sample of lead-lead collisions recorded in 2018 by the CMS experiment at a nucleon-nucleon center-of-mass energy of $\sqrt{s_{_{\mathrm{NN}}}} =$ 5.02 TeV, corresponding to an integrated luminosity of $1.7\pm0.1\,\mathrm{nb}^{-1}$. Top quark pair ($\mathrm{t\bar{t}}$) production is measured in events with two opposite-sign high-$p_\mathrm{T}$ isolated leptons ($\ell^\pm\ell^\mp =\,\mathrm{e}^{+} \mathrm{e}^{-},\,μ^{+} μ^{-},\,\mathrm{and}\,\mathrm{e}^{\pm} μ^{\mp}$). We test the sensitivity to the $\mathrm{t\bar{t}}$ signal process by requiring or not the additional presence of b-tagged jets, and hence demonstrate the feasibility to identify top quark decay products irrespective of interacting with the medium (bottom quarks) or not (leptonically decaying W bosons). To that end, the inclusive cross section ($σ_\mathrm{t\bar{t}}$) is derived from likelihood fits to a multivariate discriminator, which includes different leptonic kinematic variables with and without the b-tagged jet multiplicity information. The observed (expected) significance of the $\mathrm{t\bar{t}}$ signal against the background-only hypothesis is 4.0 (5.8) and 3.8 (4.8) standard deviations, respectively, for the fits with and without the b-jet multiplicity input. After event reconstruction and background subtraction, the extracted cross sections are $σ_\mathrm{t\bar{t}} = 2.03 ^{+0.71}_{-0.64}$ and $2.54 ^{+0.84}_{-0.74}\,μ\mathrm{b}$, respectively, which are lower than, but still compatible with, the expectations from scaled proton-proton data as well as from perturbative quantum chromodynamics predictions. This measurement constitutes the first crucial step towards using the top quark as a novel tool for probing strongly interacting matter.
