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

粒子物理的标准模型(SM)，大约有半个世纪的历史，似乎经受住了许多严格的考验 实验测试，最终导致了最近发现的希格斯粒子。然而，它留下了一些关键的 悬而未决的问题，激励人们继续寻找物理学之外的证据：来自加速器的新粒子 或外星来源，与预期的守恒定律或其他SM预测“不符合”的新相互作用， 诸若此类。 美国布鲁克海文国家实验室(BNL)的实验人员利用 亚原子粒子称为介子，很容易在粒子加速器中产生，但不是正常粒子的组成部分 物质。他们测量了介子的反常磁矩a_u，精确度令人难以置信，达到了0.54ppm 百万美元。但是，a_mu值并不完全符合SM的预期。 为了提高精确度，这可能代表着令人信服的新物理学的发现，BNL的实验是 美国费米国家实验室(FNAL)用许多相同的技术进行了改进，重新创造了这种物质。一大堆 日本的J-PARC提出了不同的测量a_u的方法，但目标相似。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 超冷介子束，其中束中单个介子的速度和方向只有很小的偏差 与他们的平均水平相比。建议通过激光电离原子束束态的类氢原子来产生这种光束。 正Muon和一个电子(Muonium，或Mu)，在二氧化硅气凝胶中形成并随后在 进入真空的室温热速度。除了启用J-PARC方案外，一种超冷极化介子 可变低能电子束将利用介子自旋技术在材料科学中开辟新的应用 薄层、曲面和材质界面中的旋转。在过去的一年里，取得了重大进展， 在温哥华TRIUMF的实验中展示了在真空中产生可行数量的热Mu。 下一步是通过激光电离这种丰富的Mu源来进一步发展超冷Muon源 英国卢瑟福·阿普尔顿实验室的脉冲光束实验。伴随着对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观测到的SM偏差是统计波动、不明系统误差或 如果这确实是超越标准模型的物理学的证据。

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.