Muon anomalous magnetic moment (g-2) and electric dipole moment at J-PARC

J-PARC 的 μ 子反常磁矩 (g-2) 和电偶极矩

• 批准号: SAPPJ-2015-00039
• 负责人: Marshall, Glen
• 金额: $ 5.83万
• 依托单位: TRIUMF
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Project
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=614425
• 关键词: Muon; anomalous; magnetic; moment; electric

The Standard Model (SM) of particle physics, about half a century old, seems to have survived the many stringent experimental tests, culminating in the recent discovery of the Higgs particle. However, it leaves some critical questions unanswered, motivating the continuing search for evidence of physics beyond: new particles from accelerators or extraterrestrial sources, new interactions that "don't fit" with expected conservation laws or other SM predictions, and so on. A tantalizing result has been obtained by experimenters at Brookhaven National Laboratory (BNL) in the US using subatomic particles called muons that are easily produced in particle accelerators, but are not a constituent of normal matter. They measured the muon's anomalous magnetic moment, a_mu, with an incredible precision of 0.54 parts per million. But the value obtained for a_mu did not quite match SM expectations. Striving for yet improved precision that might represent convincing discovery of new physics, the BNL experiment is being recreated with improvements at the US Fermi National Laboratory (FNAL) with many of the same techniques. A much different method to measure a_mu, but with similar goals, has been proposed at J-PARC in Japan. The J-PARC scheme requires significant development of several experimental aspects, perhaps the most challenging being the production of a beam of ultra-cold muons, where the speeds and directions of the individual muons in the beam have only a tiny deviation from their average. It is proposed to create this beam by laser ionization of the hydrogen-like atomic bound state of a positive muon and an electron (muonium, or Mu), after formation in silica aerogel and subsequent diffusion at room-temperature thermal velocities into vacuum. In addition to enabling the J-PARC scheme, an ultra-cold polarized muon beam of variable low energy would open up new applications in materials science with the techniques of muon spin rotation in thin layers, surfaces, and material interfaces. In the past year, significant progress has been achieved, with production of viable amounts of thermal Mu in vacuum demonstrated in experiments at TRIUMF in Vancouver. The next step is to develop further the ultra-cold muon source by laser ionization of this abundant source of Mu in pulsed beam experiments at Rutherford Appleton Laboratory in the UK. Along with the control of systematic uncertainties made possible by J-PARC methods, this should open the way for independent experimental confirmation of whether the deviation from the SM observed at BNL is the result of a statistical fluctuation, an unidentified systematic error, or if it is indeed evidence of physics beyond the Standard Model.

粒子物理学的标准模型（SM），大约有半个世纪的历史，似乎经历了许多严格的考验。 实验测试，最终在最近发现的希格斯粒子。然而，它留下了一些关键的 没有答案的问题，激发了继续寻找物理学证据的动力：来自加速器的新粒子 或外星来源，新的相互作用，“不适合”与预期的守恒定律或其他SM预测， 等 美国布鲁克海文国家实验室（BNL）的实验人员使用 亚原子粒子，称为μ子，很容易在粒子加速器中产生，但不是正常粒子的组成部分。 所谓了他们测量了μ子的反常磁矩a_mu，其精确度令人难以置信，达到了0.54分之一。 万但是a_mu的值与SM的期望值不太匹配。 BNL实验致力于提高精度，这可能代表新物理学的令人信服的发现， 在美国费米国家实验室（FNAL）用许多相同的技术进行了改进。得多 在日本的J-PARC已经提出了不同的方法来测量a_mu，但是具有相似的目标。J-PARC方案 需要几个实验方面的重大发展，也许最具挑战性的是生产一个 超冷μ子束，其中束中单个μ子的速度和方向只有微小的偏差 从他们的平均水平。有人建议通过激光电离类氢原子的束缚态来产生这种光束， 正μ介子和电子（μ 鎓，或Mu），在二氧化硅气凝胶中形成后， 室温热速度进入真空。除了启用J-PARC方案外，超冷极化μ子 可变低能束流将通过μ子自旋技术在材料科学中开辟新的应用 薄层、表面和材料界面中的旋转。在过去一年中，取得了重大进展， 在温哥华的TRIUMF实验中证明了在真空中产生可行量的热Mu。 下一步是通过激光电离这种丰富的μ源，进一步开发超冷μ子源。 脉冲束实验在卢瑟福阿普尔顿实验室在英国。沿着系统不确定性的控制 通过J-PARC方法，这应该为独立的实验确认是否 在BNL观察到的SM偏差是统计波动、未识别的系统误差或 如果它确实是超越标准模型的物理学的证据。