Electron-positron pair production

当一个电子击中它的反粒子，一个正电子，两者都可以湮灭成两个光子形式的纯电磁能量。这一反应是爱因斯坦质量和能量等价性的一个显著例子。从原理上讲，相反的过程也是可能的：相互碰撞的光子可以通过形成电子-正电子对将其能量转化为质量。到目前为止，这种纯粹由光子光束产生物质的基本量子过程--以布莱特和惠勒的名字命名--无法在实验中直接观察到，因为获得可探测信号的要求非常高。由于高强度激光技术的持续进步，目前这种情况正在改变。当极强的光学激光脉冲与高频光子束(例如来自韧致辐射)碰撞时，可能会发生强场版本的Breit-Wheeler过程：在光子-多光子碰撞中产生电子-正电子对。在非微扰参数的相关范围内，迄今未被观测到的产生机制类似于场诱导的隧穿过程，通过该过程，量子真空衰变为大质量粒子。然而，所需的场强只能通过激光的紧密聚焦来实现。鉴于计划中的实验研究，本项目的目标是为聚焦高强度激光脉冲中Breit-Wheeler对的产生提供理论预测。这带来了一个巨大的挑战，必须通过适当的科学方法组合来克服：获得所产生粒子的总产生概率和动量谱的解析S矩阵计算与基于通过弗拉索夫方程对该过程的多体描述的数值模拟相结合。这两种方法都可以很好地相互补充和放大。此外，在第二个资助期间，我们将研究相对论粒子束(电子或裸离子)与聚焦激光脉冲碰撞中多光子三叉戟和Bethe-Heitler对产生的密切相关过程，特别关注与强场Breit-Wheeler过程的异同。除了克服计算挑战，我们的目标是回答概念性问题，例如如何将辐射反应一致地纳入超高强度对子产生的理论处理中。相应的解可以对更好地理解极场条件下的量子真空做出重要贡献。

When an electron hits its antiparticle, a positron, both can annihilate into pure electromagnetic energy in the form of two photons. This reaction represents a striking example of Einstein‘s equivalence between mass and energy. In principle, the inverse process is possible as well: photons colliding with each other can transform their energy into mass by forming an electron-positron pair. Until now, this fundamental quantum process of matter creation purely from photon beams - which is named after Breit and Wheeler - could not directly be observed in experiment, though, since the requirements for obtaining a detectable signal are very high.Due to a sustained progress in high-intensity laser technology, the situation is currently changing. When an extremely intense optical laser pulse collides with a high-frequency photon beam (e.g. from bremsstrahlung), a strong-field version of the Breit-Wheeler process may occur: electron-positron pairs are created in photon-multiphoton collisions. In the relevant domain of nonperturbative parameters, the hitherto unobserved creation mechanism resembles a field-induced tunneling process by which the quantum vacuum decays into massive particles. However, the required field intensities can only be achieved by tight focusing of the laser light. Thereby a very complex spatio-temporal structure is imprinted on the electromagnetic fields.In view of planned experimental studies, the goal of the present project is to provide theoretical predictions for Breit-Wheeler pair production in focused high-intensity laser pulses. This poses a formidable challenge that shall be overcome by a suitable combination of scientific methods: analytical S-matrix calculations to obtain total production probabilities and momentum spectra of created particles are combined with numerical simulations based on a many-body description of the process via Vlasov equations. Both approaches can complement and amplify each other very well. In addition, during the second funding period, the closely related processes of multiphoton trident and Bethe-Heitler pair production in collisions of relativistic particle beams (electrons or bare ions) with focused laser pulses will be studied, with special attention being paid to similarities and differences with the strong-field Breit-Wheeler process.Aside from passing the computational challenges, we aim at answering conceptual questions, e.g. how radiation reaction can be incorporated consistently into the theoretical treatment of pair creation at ultrahigh intensities. Corresponding solutions can make important contributions to an improved understanding of the quantum vacuum under extreme-field conditions