Enhancing The MIGDAL Experiment's Sensitivity in the Low Energy Regime Relevant to Dark Matter Searches

在过去的几年里，Arkady Migdal在20世纪30年代末做出的一个模糊的量子力学预测彻底改变了对暗物质（DM）的研究。仅基于理论论证，Migdal效应已被调用，以将世界领先的DM实验的DM质量灵敏度提高2个数量级。该效应预测原子核受到一个小的“反冲”会导致原子电子的发射。当反冲来自非常轻的DM粒子时，反冲核在探测器中沉积的能量太小而无法探测到，但伴随的电子发射是可以探测到的。然而，在这一制度中没有观察到这种效果，这就对这些解释的有效性提出了疑问。鉴于Migdal效应对DM检测的潜在影响，非常需要对该效应进行实验验证。该奖项将用于对DM搜索的一些感兴趣的原子的Migdal效应进行明确的检测。该方法利用PI小组在开发探测器方面的最新进展来成像和分辨低能粒子轨道。有了这种能力，一个Migdal事件可以清楚地确定通过重建电子和核反冲轨道偏离一个共同的相互作用点。作为国际MIGDAL合作的成员，PI将参与在英国专门设计的设施中检测效果的实验。基于第一次检测的详细研究将用于约束在DM实验中利用的能量以上的理论预测。UNM正在开发将搜索扩展到较低能量所需的新型探测器，如果成功，将在该项目的第二阶段部署。该项目将培训本科生和研究生，并让他们参与实验的各个方面。这将包括在设计，测试和操作小型台式探测器和开发新的图像处理技术来模拟和分析数据的实践经验。该项目将通过探测和研究暗物质目标原子中的中子诱发核反冲来评估利用米格达尔效应设定暗物质极限的有效性。它利用了PI小组的最新进展，展示了光学时间投影室（OTPC）中低能电离轨道的高空间分辨率和高信噪比成像，这使得粒子识别和重建其沿轨道沿着运动的方向。有了这种能力，Migdal事件的拓扑结构，可以清楚地确定通过重建的电子和核反冲轨道偏离的相互作用点。这些初步发现是欧洲资助的MIGDAL实验的基础，该实验将于秋季开始。该奖项将为积极参与实验的所有阶段提供支持，从数据采集到模拟和分析。该项目的一个关键目标是将搜索扩展到较低的能量，接近DM感兴趣的能量。这将涉及开发新的图像处理技术和一种新的负离子OTPC，其具有低能量区域所需的精致空间分辨率。如果成功，这项技术将在MIGDAL实验的第二阶段实施。该奖项还将支持培训和广泛的研究经验，以多样化的本科生和研究生在越来越罕见的小规模实验。凭借其新颖的功能，NID OTPC有望影响跨科学的广泛应用。这些包括X射线偏振测量、暗光子和双β搜索、罕见核衰变、低背景α和中子测量等。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Over the past few years, an obscure quantum mechanical prediction made by Arkady Migdal in the late 1930’s has revolutionized the search for dark matter (DM). The Migdal effect has been invoked, based on theoretical arguments alone, to improve the DM mass-sensitivity of the world-leading DM experiment by 2 orders of magnitude. The effect predicts that an atomic nucleus receiving a small “kick” can result in the emission of an atomic electron. When the kick is from very light DM particles, the energy deposited in the detector by the recoiling nucleus is too small to detect, but the accompanying electron emission is detectable. The effect, however, has not been observed in this regime, raising questions on the validity of these interpretations. Given the potential impact of the Migdal effect on DM detection, an experimental verification of the effect is very much needed. This award will be used to make an unambiguous detection of the Migdal effect for a number of atoms of interest for DM searches. The method leverages recent progress in the PI’s group on developing detectors to image and resolve low energy particle tracks. With this capability, a Migdal event can be clearly identified by reconstructing the electron and nuclear recoil tracks diverging from a common interaction point. As a member of the international MIGDAL collaboration, the PI will participate in experiments to detect the effect at a specially designed facility in the UK. The detailed studies based on the first detection will be used to constrain theoretical predictions at energies above those being exploited in DM experiments. Novel detectors needed to extend the search to lower energies are being developed at UNM and, if successful, will be deployed in the second phase of this project. The project will train and involve undergraduate and graduate students in all aspects of the experiment. This will include hands-on experience in designing, testing and operating small table-top detectors and developing novel image processing techniques to simulate and analyze the data. This project will evaluate the validity of using the Migdal effect for setting dark matter (DM) limits by detecting and studying it in neutron-induced nuclear recoils in target atoms of interest for DM. It leverages recent progress in the PI’s group demonstrating high spatial resolution and high signal-to-noise imaging of low energy ionization tracks in an optical time-projection chamber (OTPC), which enables particle identification and reconstruction of its direction of motion along the track. With this capability, the Migdal event topology can be clearly identified by reconstructing the electron and nuclear recoil tracks diverging from the interaction point. These preliminary findings are the basis of a funded European MIGDAL experiment to begin in the Fall. This award will provide support to actively participate in all phases of the experiment, from data taking to simulations and analysis. A key goal of the project is to expand the search to lower energies, approaching those of interest to DM. This will involve developing novel image processing techniques and a novel negative ion OTPC with the exquisite spatial resolution needed for the low energy regime. If successful, this technology will be implemented in the second phase of the MIGDAL experiment. This award will also support training and a wide range of research experience to a diverse set of undergraduates and graduate students in increasingly rare small-scale experiments. With its novel capabilities, the NID OTPC promises to impact a broad range of applications across the sciences. These include X-ray polarimetry, dark-photon and double-beta searches, rare nuclear decays, low background alpha and neutron measurements and others.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.