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arXiv 1811.08780hep-ex
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用LHC上的ATLAS探测器在$\sqrt{s}=13$ TeV上与顶夸克对相关的瞬发光子产生的基准截面测量

Fiducial cross-section measurements of the production of a prompt photon in association with a top-quark pair at $\sqrt{s}=13$ TeV with the ATLAS detector at the LHC

Joshua Wyatt Smith

摘要:

用ATLAS探测器在质量中心能量为13 TeV的基准体积中测量了与光子相关的顶夸克对产生的截面。结果使用LHC在2015年和2016年收集的质子-质子碰撞数据,总计36.1 fb $^{-1}$。这也是在双轻子通道中进行的第一次$t\bar{t}γ$截面测量。根据径迹和量热计的信息,只有一个光子才具有$p_{\text{T}} > 20$ GeV,并被隔离。在双轻子(单轻子)通道中至少需要两(四)个喷流,其中至少一个喷流来自$b$ -夸克。两个独立的神经网络算法用于帮助减少背景在最终测量中的影响。提示光子标记器接受来自量热计中能量沉积的信息的训练,以区分提示光子和强子假光子。该神经网络的输出被馈送到事件级鉴别器中,该事件级鉴别器使用事件信息将信号从所有背景的总和中分类。对事件级鉴别器的输出执行最大似然拟合,以确定信号过程的基准横截面。单轻子和双轻子通道的基准截面分别为$521 \pm 9 \text{(stat.)} \pm 41 \text{(sys.)}$ fb和$69 \pm 3 \text{(stat.)} \pm 4\text{(sys.)}$ fb。总共进行了八次截面测量,所有测量结果均与理论上的次-前序预测一致。

英文摘要:

The cross sections for top-quark pair production in association with a photon are measured in a fiducial volume with the ATLAS detector at a centre-of-mass energy of 13 TeV. Results are presented using proton-proton collision data collected by the LHC during 2015 and 2016, amounting to a total of 36.1 fb$^{-1}$. This also presents the first $t\bar{t}γ$ cross-section measurements performed in the dilepton channels. Exactly one photon is required to have $p_{\text{T}} > 20$ GeV and be isolated based on track and calorimeter information. At least two (four) jets are required in the dilepton (single-lepton) channels, with at least one jet originating from a $b$-quark. Two separate neural network algorithms are used to help reduce the impact backgrounds play in the final measurements. The Prompt Photon Tagger is trained on information from energy deposits in the calorimeters to distinguish prompt photons from hadronic fake photons. The output of this neural network is fed into the Event-level Discriminator that uses event information to classify signal from the sum of all backgrounds. A maximum likelihood fit is performed on the output of the Event-level Discriminator to determine the fiducial cross section of the signal process. The fiducial cross section for the single-lepton and dilepton channel are measured to be $521 \pm 9 \text{(stat.)} \pm 41 \text{(sys.)}$ fb and $69 \pm 3 \text{(stat.)} \pm 4\text{(sys.)}$ fb, respectively. In total, eight cross-section measurements are performed and all agree with theoretical next-to-leading-order predictions.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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