标题： FACET-II加速器320实验中产生和探测Breit-Wheeler隧道正电子的前景 显示英文标题

标题： Prospects for the production and detection of Breit-Wheeler tunneling positrons in Experiment 320 at the FACET-II accelerator

摘要： SLAC 实验 320 将 10 束 TW 级激光脉冲与 FACET-II RF 直线加速器产生的高质量 10 GeV 电子束碰撞。 预计通过强场隧穿机制的非线性 Breit-Wheeler 机制，该设置将在每次碰撞中产生一定数量的$e^+e^-$对，估计产额为 ~0.01-0.1 对。 通常，这种小信号率伴随着来自背景的大信号，例如来自高电荷主电子束的耗尽、束晕引起的次级粒子、以及电子-激光碰撞本身产生的光子和低能电子。 这些背景可能在传感元件表面达到 O(100) 个/cm² 的带电粒子密度（甚至更多中性粒子），使得单粒子的明确检测成为一个巨大的挑战。 在这项工作中，我们展示了如何采用来自高能物理实验的探测器和方法来实现这一测量。 所提出的解决方案基于高度分层的多层辐射硬化像素探测器，并结合强大的粒子跟踪算法。 使用现有实验装置的详细模拟，我们展示了如何在完全重建后，将由于背景过程引起的误检率降低一个以上数量级。 此外，我们还表明，可实现的高空间跟踪分辨率（<10 微米）允许对正电子动量进行 <2% 分辨率的测量，从而实现非线性 Breit-Wheeler 过程的谱特性表征。 基于我们的广泛模拟，并假设保守的大量背景，我们证明了在即将进行的 E320 数据采集活动中可以测量单个 Breit-Wheeler 正电子。 这将是首次在（深）隧穿机制下对该难以捉摸的过程进行具有统计显著性的观测和表征。 显示英文摘要

摘要： The SLAC Experiment 320 collides 10 TW-class laser pulses with the high-quality, 10 GeV electron beam from the FACET-II RF LINAC. This setup is expected to produce a sizable number of $e^+e^-$ pairs via nonlinear Breit-Wheeler mechanism in the strong-field tunneling regime, with an estimated yield of ~0.01-0.1 pairs per collision. This small signal rate typically comes along with large backgrounds originating, e.g., from dumping the high-charge primary beam, secondaries induced by the beam halo, as well as photons and low-energy electrons produced in the electron-laser collision itself. These backgrounds may reach densities of O(100) charged particles per cm^2 (and even more neutral particles) at the surface of the sensing elements, making it a tremendous challenge for an unambiguous detection of single particles. In this work, we demonstrate how detectors and methods adapted from high-energy physics experiments, can enable this measurement. The solution presented is based on a highly granular, multi-layer, radiation-hard pixel detector paired with powerful particle-tracking algorithms. Using a detailed simulation of the existing experimental setup, we show how the false-positive rate due to background processes can be reduced by more than an order of magnitude relative to the expected signal after full reconstruction. Furthermore, we show that the high spatial tracking resolution achievable (<10 microns) allows for positron momentum measurements with a resolution of <2%, enabling spectral characterization of the nonlinear Breit-Wheeler process. Based on our extensive simulation, with a conservatively large background assumption, we show that it is possible to measure single Breit-Wheeler positrons in the coming data taking campaign of E320. That would be the first statistically significant observation and characterization of this elusive process in the (deep) tunneling regime.