We review the current understanding of time-like virtual photon emission from QCD matter. The phenomenology of dilepton emission is discussed and basic theoretical concepts are introduced. The experimental findings are presented, grouped into production of lepton pairs in elementary processes, production off cold nuclear matter and emission from heavy-ion collisions. The review emphasizes the role of dilepton emission as tool for studying exotic phases of QCD matter. Open questions and a route to probe the QCD phase diagram with dileptons are outlined.

中文翻译：

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来自强相互作用系统的双轻子辐射

我们回顾了当前对 QCD 物质类时间虚拟光子发射的理解。讨论了双轻子发射的现象学，并介绍了基本的理论概念。展示了实验结果，分为基本过程中轻子对的产生、冷核物质的产生和重离子碰撞的发射。该评论强调了双轻子发射作为研究 QCD 物质奇异相的工具的作用。概述了未解决的问题和用双光子探测 QCD 相图的途径。