Search for an Electric Dipole Moment of 199Hg

令人信服的科学证据表明，宇宙是在大约130亿年前的一次“大爆炸”中进化而来的。与大爆炸假说相关的一个悬而未决的主要问题是，为什么宇宙中的物质比反物质多；它们应该是等量的。这个问题的可能答案是，在自然界中有一种未知的力量，极其微弱，倾向于物质而不是反物质。很容易证明，如果这种新的力存在，它将赋予基本粒子和原子一种被称为“电偶极矩”的特性，即沿着粒子或原子的自旋轴的电荷的微小分离。对199Hg（汞原子的自旋1 / 2同位素）的电偶极矩的测量将为这种打破物质和反物质之间对称性的新力提供明确的证据。这个项目促进了科学的进步，符合国家利益。对构成宇宙的粒子和控制粒子之间相互作用的自然法则的研究有助于增进我们对物理世界的理解，并刺激从这种理解中产生的技术发展。以前的实验不够灵敏，无法探测到原子或粒子的电偶极矩。199Hg项目将构成有史以来最灵敏的电偶极矩搜索。因此，它将为学生提供最先进的实验原子物理技术和高精度测量技术的优秀培训。该项目将推动核自旋磁强计领域的发展，该领域在一般的磁场测量中具有广泛的应用。社会将受益于新一代科学家的培养和对我们所生活的宇宙更全面的了解。高精度的桌面实验，例如199Hg项目，为粒子加速器探索潜在的对称性和自然力提供了补充途径。原子的电偶极矩只有在违反时间反转(T)对称的情况下才存在，而T对称违反与物质/反物质不对称直接相关（通过CPT定理）。一种方法是通过观察199Hg原子的原子拉莫尔（自旋进动）频率的变化来测量电偶极矩，因为外部电场作用于含有这些原子的蒸气池。这个实验将在一个共同的磁场中使用四个蒸汽电池堆叠。相反方向的电场将被应用于最里面的两个蒸汽细胞，而外面的两个细胞，没有电场，将作为共磁力计。原子将使用254 nm的共振激光进行自旋极化，而拉莫尔频率将通过穿过蒸汽电池的非共振激光的偏振旋光度来读出。先前的实验受磁场梯度的限制，实现了199Hg电偶极矩的上限小于3 × 10-30 e-cm。新实验将改善磁场均匀性，使实验灵敏度达到10-31 e-cm范围。

Compelling scientific evidence points to the conclusion that the universe evolved from a "Big Bang" some 13 billion years ago. A major unanswered question associated with the Big Bang hypothesis is why there is more matter in the universe than anti-matter; they should have been created in equal quantities. The likely answer to this question is that there is an unknown force in nature, extremely weak, that favors matter over anti-matter. It is straightforward to show that if this new force exists, it will endow elementary particles and atoms with a property known as an "electric dipole moment", a small separation of electric charge along the spin axis of the particle or atom. A measurement of the electric dipole moment of 199Hg (the spin ½ isotope of mercury atoms) will provide unambiguous evidence for this new force that breaks the symmetry between matter and anti-matter. The project serves the national interest by promoting the progress of science. The study of the particles that constitute the universe and the laws of nature that govern interactions between the particles serve to advance our understanding of the physical world and stimulate the development of technologies that have arisen from that understanding. Previous experiments have not been sensitive enough to detect the electric dipole moment of atoms or particles. The 199Hg project will constitute the most sensitive electric dipole moment search ever conducted. As such, it will provide excellent training for students in state-of-the-art experimental atomic physics techniques and high precision measurement techniques. The project will advance the field of nuclear spin magnetometry, which has broad application to measurements of magnetic fields in general. Society will benefit from the training of a new generation of scientists and from a more complete understanding of the universe we live in.High precision table-top experiments, such as this 199Hg project, provide a complementary path to particle accelerators for probing the underlying symmetries and forces of nature. An electric dipole moment of an atom can only exist if time-reversal (T) symmetry is violated, and T symmetry violation is directly related to the matter/anti-matter asymmetry (through the CPT theorem). One measures an electric dipole moment by observing a change in the atomic Larmor (spin precession) frequency of the 199Hg atoms as an external electric field is applied to vapor cells that contain the atoms. This experiment will use a stack of four vapor cells in a common magnetic field. Oppositely directed electric fields will be applied to the two innermost vapor cells while the outer two cells, with no electric fields, will serve as co-magnetometers. The atoms will be spin polarized using resonant 254 nm laser light and the Larmor frequencies will be read-out by the optical rotation of the polarization of non-resonant laser light that traverses the vapor cells. A previous experiment, limited by gradients in the magnetic field, achieved an upper limit on the electric dipole moment of 199Hg of less than 3 x 10-30 e-cm. this new experiment will improve the magnetic field uniformity to push the experimental sensitivity into the 10-31 e-cm range.