RUI: Search for Anomalous Proton Spin Interactions with A Dual-Isotope Rubidium Magnetometer

该奖项支持继续使用双同位素铷（Rb）磁强计的研究计划，以寻找Rb核自旋与地球质量之间的假想远程耦合。它还将支持研究探索使用双同位素Rb磁力计和相关实验技术来寻找异常的中程（超过一米的距离尺度）和短程（超过一纳米的距离尺度）自旋-自旋耦合。双同位素Rb磁强计对质子的非磁性、自旋依赖相互作用特别敏感，因此质子自旋的异常相互作用会产生Rb自旋进动频率之间的微分位移，而大多数系统误差源会产生自旋进动频率的共模位移，这可以通过辅助测量来控制。最近对类似效应的大多数研究都限制了中子或电子自旋的异常耦合，因此该实验在一定程度上搜索了一个参数空间，取决于理论模型，与先前实验约束的参数空间正交。优化后的双同位素Rb磁强计具有足够的射噪声投影灵敏度，可以将远程自旋-质量耦合的实验极限提高一个数量级，特别是质子自旋的实验极限提高两个数量级，并将异常自旋-自旋耦合的实验极限提高一个数量级以上。人们对无质量标量场/伪标量场的引力标量张量理论重新产生了兴趣，因为它们可以解释最近在宇宙距离上观测到的“暗能量”。这种场的伪标量分量在自旋和地球引力场之间产生了远距离的相互作用。在最简单的标量张量理论中，这种相互作用导致自旋进动频率的移动小于目前的限制，但正好在本实验的范围内。探测到这种类型的相互作用将证明引力违反宇称和时间反转对称性，以及广义相对论基础上的等效原理。与广义相对论相一致的结果仍将为许多替代理论提供新的测试，例如假设反常自旋-质量和自旋-自旋耦合的扭转引力。作为加州州立大学东湾分校历史上唯一一个由外部资助的物理实验项目，该研究项目在过去三年中使物理学专业的学生人数增加了两倍，16名学生（包括4名女性和9名少数族裔学生）为该项目做出了有意义的贡献。

This award supports continuation of a research program using a dual-isotope rubidium (Rb) magnetometer to search for a hypothetical long-range coupling between Rb nuclear spins and the mass of the earth. It will also support research to explore use of the dual-isotope Rb magnetometer and related experimental techniques to search for anomalous intermediate-range (over distance scales of about one meter) and short-range (over distance scales of about one nanometer) spin-spin couplings. The dual-isotope Rb magnetometer is particularly sensitive to non-magnetic, spin-dependent interactions of the proton so that anomalous interactions of the proton spin produce a differential shift between the Rb spin-precession frequencies, whereas most sources of systematic error produce common-mode shifts of the spin-precession frequencies which can be controlled through auxiliary measurements. The majority of recent searches for similar effects limit anomalous couplings of either the neutron or electron spin, so the proposed experiment searches a parameter space to some degree, depending on the theoretical model, orthogonal to that constrained by previous experiments. The optimized dual-isotope Rb magnetometer has sufficient shot-noise-projected sensitivity to improve experimental limits on long-range spin-mass couplings by an order of magnitude in general and by two orders of magnitude for the proton spin in particular, and improve limits on anomalous spin-spin couplings by over an order of magnitude.There is renewed interest in scalar-tensor theories of gravity with massless scalar/pseudoscalar fields since they can explain the recent observation of "dark energy" over cosmological distances. The pseudoscalar component of such a field generates a long-range interaction between spins and the gravitational field of the Earth. This interaction in the simplest scalar-tensor theory causes a shift of the spin precession frequencies smaller than present limits but just within the range of this experiment. Detection of this type of interaction would be evidence that gravity violated parity and time-reversal symmetries, as well as the equivalence principle which underlies the theory of general relativity. A result consistent with general relativity would still provide new tests of numerous alternative theories, such as torsion gravity, that hypothesize anomalous spin-mass and spin-spin couplings. As the only externally funded physics experiment in the history of California State University / East Bay, this research program has led to tripling the number of physics majors in the past three years and sixteen students, including four women and nine underrepresented minority students, have made meaningful contributions to the project.