Light-by-light scattering (γγ γγ) is a quantum-mechanical process that is forbidden in the classical theory of electrodynamics. This reaction is accessible at the Large Hadron Collider thanks to the large electromagnetic field strengths generated by ultra-relativistic colliding lead ions. Using 480 μb⁻¹ of lead–lead collision data recorded at a centre-of-mass energy per nucleon pair of 5.02 TeV by the ATLAS detector, here we report evidence for light-by-light scattering. A total of 13 candidate events were observed with an expected background of 2.6 ± 0.7 events. After background subtraction and analysis corrections, the fiducial cross-section of the process Pb + Pb (γγ) Pb^(∗) +  Pb^(∗)γγ, for photon transverse energy E_T > 3 GeV, photon absolute pseudorapidity |η| < 2.4, diphoton invariant mass greater than 6 GeV, diphoton transverse momentum lower than 2 GeV and diphoton acoplanarity below 0.01, is measured to be 70 ± 24 (stat.) ± 17 (syst.) nb, which is in agreement with the standard model predictions.

中文翻译：

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大型强子对撞机与ATLAS探测器发生重离子碰撞时的逐光散射证据

光通过光散射（γ γ γ γ）是在电动力学的经典理论禁止量子力学过程。由于超相对论性碰撞铅离子产生了巨大的电磁场强度，因此在大型强子对撞机中可以进行此反应。使用由ATLAS探测器在每个核对对5.02 TeV的质心能量中心记录的 480μb ^-1铅-铅碰撞数据，在此我们报告了逐光散射的证据。总共观察到13个候选事件，预期背景为2.6±0.7个事件。背景扣除后和分析的校正，该方法的基准横截面的Pb + PB（γ γ）铅^（*） + PB ^（*）γ γ，用于光子横向能量ë _Ť > 3 电子伏特，光子绝对赝| η | <2.4，双光子不变质量大于6 GeV，双光子横向动量小于2  GeV，双光子共面性小于0.01，测得值为70±24（标准）±17（系统）nb，与标准一致模型预测。