Search for an Electric Dipole Moment of 199Hg

寻找 199Hg 的电偶极矩

• 批准号: 1707573
• 负责人: Blayne Heckel
• 金额: $ 57.4万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1707573&HistoricalAwards=false
• 关键词: Search; Electric; Dipole; Moment; 199Hg

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.

令人信服的科学证据表明，宇宙是从大约130亿年前的“大爆炸”演变而来的。与大爆炸假说相关的一个主要未回答的问题是为什么宇宙中的物质比反物质多;它们应该以相等的数量被创造出来。这个问题可能的答案是，自然界中存在一种未知的力量，非常微弱，有利于物质而不是反物质。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”的性质，即电荷沿着粒子或原子的自旋轴的微小分离。对199 Hg（汞原子的自旋1/2同位素）的电偶极矩的测量将为这种破坏物质和反物质之间对称性的新作用力提供明确的证据。该项目通过促进科学进步来服务于国家利益。对构成宇宙的粒子和支配粒子之间相互作用的自然规律的研究有助于促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的发展。以前的实验没有足够的灵敏度来检测原子或粒子的电偶极矩。1999年汞项目将是有史以来进行的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良好培训。该项目将推动核自旋磁力测量领域的发展，该领域在一般磁场测量方面有着广泛的应用。社会将受益于新一代科学家的培训和对我们所生活的宇宙的更全面的了解。高精度的桌面实验，如199 Hg项目，为粒子加速器探索基本的对称性和自然力提供了一条补充途径。原子的电偶极矩只有在时间反演（T）对称性被破坏时才能存在，而T对称性破坏与物质/反物质不对称性直接相关（通过CPT定理）。一种测量电偶极矩的方法是观察199 Hg原子的拉莫尔（自旋进动）频率的变化，因为外部电场施加到包含原子的蒸汽单元。这个实验将在一个共同的磁场中使用一堆四个蒸汽电池。将向两个最里面的蒸汽室施加不透明的定向电场，而没有电场的外部两个室将用作共磁力计。原子将使用共振254 nm激光进行自旋极化，并且拉莫尔频率将通过穿过蒸气室的非共振激光的偏振的旋光读出。之前的实验，由于受到磁场梯度的限制，达到了199 Hg的电偶极矩小于3 x 10-30 e-cm的上限。这一新的实验将改善磁场均匀性，以将实验灵敏度推到10-31 e-cm范围内。