Physics Department, University of Toronto, Toronto, Ontario M5S 1A7, Canada.
Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada.
Phys Rev Lett. 2013 Nov 27;111(22):221803. doi: 10.1103/PhysRevLett.111.221803.
New sub-GeV gauge forces ("dark photons") that kinetically mix with the photon provide a promising scenario for MeV-GeV dark matter and are the subject of a program of searches at fixed-target and collider facilities around the world. In such models, dark photons produced in collisions may decay invisibly into dark-matter states, thereby evading current searches. We reexamine results of the SLAC mQ electron beam dump experiment designed to search for millicharged particles and find that it was strongly sensitive to any secondary beam of dark matter produced by electron-nucleus collisions in the target. The constraints are competitive for dark photon masses in the ~1-30 MeV range, covering part of the parameter space that can reconcile the apparent (g-2)(μ) anomaly. Simple adjustments to the original SLAC search for millicharges may extend sensitivity to cover a sizable portion of the remaining (g-2)(μ) anomaly-motivated region. The mQ sensitivity is therefore complementary to ongoing searches for visible decays of dark photons. Compared to existing direct-detection searches, mQ sensitivity to electron-dark-matter scattering cross sections is more than an order of magnitude better for a significant range of masses and couplings in simple models.
新的亚GeV 量级规范力（“暗光子”）与光子混合，为 MeV-GeV 暗物质提供了一个很有前景的场景，也是世界各地固定靶和对撞机设施进行搜索的计划的主题。在这样的模型中，在碰撞中产生的暗光子可能不可见地衰变为暗物质状态，从而逃避当前的搜索。我们重新审视了 SLAC mQ 电子束dump 实验的结果，该实验旨在寻找毫电荷粒子，发现它对靶中电子-核碰撞产生的任何暗物质次级束都非常敏感。对于~1-30 MeV 范围内的暗光子质量，这些约束是有竞争力的，涵盖了可以调和明显的（g-2)(μ)异常的部分参数空间。对原始 SLAC 毫电荷搜索的简单调整可能会扩展灵敏度，覆盖剩余的（g-2)(μ)异常动机区域的相当一部分。因此，mQ 的灵敏度与正在进行的暗光子可见衰变搜索互补。与现有的直接探测搜索相比，mQ 对电子-暗物质散射截面的灵敏度在简单模型中对质量和耦合的一个重要范围的灵敏度提高了一个数量级以上。
