重离子碰撞中光子和双轻子产生的磁声致发光及其特征
The Magneto-Sono-Luminescence and its signatures in photon and dilepton production in heavy ion collisions
摘要：
重离子碰撞早期产生的物质主要由胶子组成，并被旁观者核子产生的相干磁场穿透。胶子物质在外部磁场中的涨落通过虚夸克环与实光子和虚光子耦合。我们研究了在相干磁场$\vec{B}$背景下应力张量$T_{μν}$的涨落对光子和双轻子产生的贡献。我们的研究扩展了我们和Skokov的早期工作，其中只考虑了应力张量$T_{μμ}$迹线的波动（$T_{μμ}$与电磁场的耦合受尺度异常的支配）。本文利用算子乘积展开（OPE）导出更一般的关系式。我们还将以前的研究扩展到双轻子的情况，这提供了区分各种生产机制的可能性。我们研究的现象包括磁声致发光（MSL，磁场$\vec{B}(x,t)$与应力张量$δT_{μν}(x,t)$的声音扰动的相互作用）和磁热致发光（MTL，$\vec{B}(x,t)$与平滑平均$<T_{μν}>$的相互作用）。我们计算了这些过程的速率，发现在重离子碰撞的早期阶段，它们可以主导光子和双轻子的产生。我们还指出了MSL和MTL的特征签名，可用于建立它们的存在和诊断所产生的物质。
英文摘要：
The matter produced in the early stages of heavy ion collisions consists mostly of gluons, and is penetrated by coherent magnetic field produced by spectator nucleons. The fluctuations of gluonic matter in an external magnetic field couple to real and virtual photons through virtual quark loops. We study the resulting contributions to photon and dilepton production that stem from the fluctuations of the stress tensor $T_{μν}$ in the background of a coherent magnetic field $\vec{B}$. Our study extends significantly the earlier work by two of us and Skokov, in which only the fluctuations of the trace of the stress tensor $T_{μμ}$ were considered (the coupling of $T_{μμ}$ to electromagnetic fields is governed by the scale anomaly). In the present paper we derive more general relations using the Operator Product Expansion (OPE). We also extend the previous study to the case of dileptons which offers the possibility to discriminate between various production mechanisms. Among the phenomena that we study are Magneto-Sono-Luminescence (MSL, the interaction of magnetic field $\vec{B}(x,t)$ with the sound perturbations of the stress tensor $δT_{μν}(x,t)$) and Magneto-Thermo-Luminescence (MTL, the interaction of $\vec{B}(x,t)$ with smooth average $<T_{μν}>$). We calculate the rates of these process and find that they can dominate the photon and dilepton production at early stage of heavy ion collisions. We also point out the characteristic signatures of MSL and MTL that can be used to establish their presence and to diagnose the produced matter.
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