报告题目：相对论重离子对撞测超强磁场和真空双折射

报告人：许长补（美国布鲁克海文国家实验室/山东大学）

报告时间：2019年9月4日（周三）下午1:30化学西楼二楼会议室

报告摘要：We presents first measurements of $e^+e^-$ pair production from linearly polarized light-light scattering accompanying the creation of a Quark-Gluon Plasma in non-central high-energy heavy ion collisions. The yields peak distinctly at low transverse momentum between 40 to 60 MeV/c and

show smooth mass distribution absent from any vector-meson contamination.

The production can be explained quantitatively with exclusive Breit-Wheeler process, creating matter from pure lights. The measured pT distributions are significantly broader than model calculation for baseline ultra-peripheral collisions where hadronic interaction does not take place and are different between Au+Au and U+U collisions.It was realized that these photons are linearly polarized and the process can be treated as polarized photons interacts with magnetic field in the Vacuum. Future polarization measurement related to the possible Vacuum birefringence will be discussed.Our experimental measurements with quantitative model calculations provide a possible tool to systematically study strong magnetic field at peta-Tesla scale controllable by varying the colliding impact parameter.