CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille, France.
Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma, USA.
Phys Rev Lett. 2019 Aug 2;123(5):052001. doi: 10.1103/PhysRevLett.123.052001.
This Letter describes the observation of the light-by-light scattering process, γγ→γγ, in Pb+Pb collisions at sqrt[s_{NN}]=5.02 TeV. The analysis is conducted using a data sample corresponding to an integrated luminosity of 1.73 nb^{-1}, collected in November 2018 by the ATLAS experiment at the LHC. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy E_{T}^{γ}>3 GeV and pseudorapidity |η_{γ}|<2.4, diphoton invariant mass above 6 GeV, and small diphoton transverse momentum and acoplanarity. After applying all selection criteria, 59 candidate events are observed for a background expectation of 12±3 events. The observed excess of events over the expected background has a significance of 8.2 standard deviations. The measured fiducial cross section is 78±13(stat)±7(syst)±3(lumi) nb.
这封信件描述了在 sqrt[s_{NN}]=5.02TeV 的 Pb+Pb 碰撞中观测到的光致轻子散射过程 γγ→γγ。该分析使用了 2018 年 11 月 ATLAS 实验在 LHC 上收集的对应于 1.73nb^{-1}积分亮度的数据样本进行。仅通过两个光子产生的事件中选择光致轻子散射候选者，每个光子的横动量 E_{T}^{γ}>3GeV，赝快度 |η_{γ}|<2.4，双光子不变质量大于 6GeV，双光子横动量和不对准性较小。在应用所有选择标准后，观察到 59 个候选事件，而预期背景为 12±3 个事件。观测到的事件超出预期背景的超额具有 8.2 个标准偏差的显著性。测量的基准截面为 78±13(stat)±7(syst)±3(lumi)nb。
