⚛️ nuclear experiments

An improved direct limit on the muon electric dipole moment

利用费米实验室 Muon g-2 实验在 2019 年至 2020 年间收集的数据，研究人员确立了关于缪子电偶极矩的新直接 95% 置信水平限制，即 $|d_\mu|<1.10\times10^{-19}~e\cdot$ cm，并发现测量值与零一致。

原作者： 2 Collaboration, D. P. Aguillard (University of Michigan, Ann Arbor, Michigan, USA), T. Albahri (University of Liverpool, Liverpool, United Kingdom), D. Allspach (Fermi National Accelerator Laboratory2 Collaboration, D. P. Aguillard (University of Michigan, Ann Arbor, Michigan, USA), T. Albahri (University of Liverpool, Liverpool, United Kingdom), D. Allspach (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), J. Annala (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), K. Badgley (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), S. Baeßler (University of Virginia, Charlottesville, Virginia, USA), L. Bailey (Department of Physics and Astronomy, University College London, London, United Kingdom), E. Barlas-Yucel (27,a), T. Barrett (Cornell University, Ithaca, New York, USA), E. Barzi (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), F. Bedeschi (INFN, Sezione di Pisa, Pisa, Italy), M. Berz (Michigan State University, East Lansing, Michigan, USA), M. Bhattacharya (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), H. P. Binney (University of Washington, Seattle, Washington, USA), P. Bloom (North Central College, Naperville, Illinois, USA), J. Bono (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), E. Bottalico (University of Liverpool, Liverpool, United Kingdom), T. Bowcock (University of Liverpool, Liverpool, United Kingdom), S. Braun (University of Washington, Seattle, Washington, USA), M. Bressler (31,a), G. Cantatore (12,b), R. M. Carey (Boston University, Boston, Massachusetts, USA), B. C. K. Casey (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), D. Cauz (25,c), R. Chakraborty (University of Kentucky, Lexington, Kentucky, USA), A. Chapelain (Cornell University, Ithaca, New York, USA), S. Chappa (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), S. Charity (University of Liverpool, Liverpool, United Kingdom), C. Chen (20,21,d), M. Cheng (University of Illinois at Urbana-Champaign, Urbana, Illinois, USA), R. Chislett (Department of Physics and Astronomy, University College London, London, United Kingdom), Z. Chu (20,d), T. E. Chupp (University of Michigan, Ann Arbor, Michigan, USA), C. Claessens (University of Washington, Seattle, Washington, USA), F. Confortini (9,e), M. E. Convery (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), S. Corrodi (Argonne National Laboratory, Lemont, Illinois, USA), L. Cotrozzi (University of Liverpool, Liverpool, United Kingdom), J. D. Crnkovic (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), S. Dabagov (8,f), P. T. Debevec (University of Illinois at Urbana-Champaign, Urbana, Illinois, USA), S. Di Falco (INFN, Sezione di Pisa, Pisa, Italy), G. Di Sciascio (INFN, Sezione di Roma Tor Vergata, Rome, Italy), S. Donati (10,g), B. Drendel (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), A. Driutti (INFN, Sezione di Pisa, Pisa, Italy, University of Kentucky, Lexington, Kentucky, USA), M. Eads (Northern Illinois University, DeKalb, Illinois, USA), A. Edmonds (Boston University, Boston, Massachusetts, USA, City University of New York at York College, Jamaica, New York, USA), J. Esquivel (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), M. Farooq (University of Michigan, Ann Arbor, Michigan, USA), R. Fatemi (University of Kentucky, Lexington, Kentucky, USA), K. Ferraby (University of Liverpool, Liverpool, United Kingdom), C. Ferrari (10,h), M. Fertl (Institute of Physics and Cluster of Excellence PRISMA++, Johannes Gutenberg University Mainz, Mainz, Germany), A. T. Fienberg (University of Washington, Seattle, Washington, USA), A. Fioretti (10,h), D. Flay (Department of Physics, University of Massachusetts, Amherst, Massachusetts, USA), S. B. Foster (2,28,i), H. Friedsam (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), N. S. Froemming (18,j), C. Gabbanini (10,h), I. Gaines (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), S. Ganguly (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), J. George (31,k), L. K. Gibbons (Cornell University, Ithaca, New York, USA), A. Gioiosa (24,l), K. L. Giovanetti (Department of Physics and Astronomy, James Madison University, Harrisonburg, Virginia, USA), P. Girotti (10,m), W. Gohn (University of Kentucky, Lexington, Kentucky, USA), L. Goodenough (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), T. Gorringe (University of Kentucky, Lexington, Kentucky, USA), J. Grange (University of Michigan, Ann Arbor, Michigan, USA), S. Grant (Argonne National Laboratory, Lemont, Illinois, USA, Department of Physics and Astronomy, University College London, London, United Kingdom), F. Gray (19,n), S. Haciomeroglu (5,o), T. Halewood-Leagas (University of Liverpool, Liverpool, United Kingdom), D. Hampai (INFN, Laboratori Nazionali di Frascati, Frascati, Italy), F. Han (University of Kentucky, Lexington, Kentucky, USA), J. Hempstead (University of Washington, Seattle, Washington, USA), D. W. Hertzog (University of Washington, Seattle, Washington, USA), G. Hesketh (Department of Physics and Astronomy, University College London, London, United Kingdom), E. Hess (10,p), A. Hibbert (University of Liverpool, Liverpool, United Kingdom), Z. Hodge (University of Washington, Seattle, Washington, USA), S. Y. Hoh (20,21,q), K. W. Hong (University of Virginia, Charlottesville, Virginia, USA), R. Hong (Argonne National Laboratory, Lemont, Illinois, USA, University of Kentucky, Lexington, Kentucky, USA), T. Hu (20,21,d), Y. Hu (20,d), M. Iacovacci (9,e), M. Incagli (INFN, Sezione di Pisa, Pisa, Italy), S. Israel (Boston University, Boston, Massachusetts, USA, Department of Physics, University of Massachusetts, Amherst, Massachusetts, USA), P. Kammel (University of Washington, Seattle, Washington, USA), M. Kargiantoulakis (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), M. Karuza (12,p), J. Kaspar (University of Washington, Seattle, Washington, USA), D. Kawall (Department of Physics, University of Massachusetts, Amherst, Massachusetts, USA), L. Kelton (Department of Physics and Astronomy, Trinity University, San Antonio, Texas, USA, University of Kentucky, Lexington, Kentucky, USA), A. Keshavarzi (Department of Physics and Astronomy, University College London, London, United Kingdom), D. S. Kessler (Department of Physics, University of Massachusetts, Amherst, Massachusetts, USA), K. S. Khaw (20,21,d), Z. Khechadoorian (Cornell University, Ithaca, New York, USA), B. Kiburg (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), M. Kiburg (Fermi National Accelerator Laboratory, Batavia, Illinois, USA, North Central College, Naperville, Illinois, USA), O. Kim (33,n), N. Kinnaird (Boston University, Boston, Massachusetts, USA), E. Kraegeloh (University of Michigan, Ann Arbor, Michigan, USA), J. LaBounty (University of Washington, Seattle, Washington, USA), K. R. Labe (Cornell University, Ithaca, New York, USA), M. Lancaster (Department of Physics and Astronomy, University of Manchester, Manchester, United Kingdom), S. Lee (Center for Axion and Precision Physics), B. Li (20,r), D. Li (20,s), L. Li (20,d), I. Logashenko (4,t), A. Lorente Campos (University of Kentucky, Lexington, Kentucky, USA), Z. Lu (20,d), A. Lucà (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), G. Lukicov (Department of Physics and Astronomy, University College London, London, United Kingdom), A. Lusiani (10,u), A. L. Lyon (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), B. MacCoy (University of Washington, Seattle, Washington, USA), R. Madrak (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), K. Makino (Michigan State University, East Lansing, Michigan, USA), S. Mastroianni (INFN, Sezione di Napoli, Naples, Italy), R. McCarthy (2,v), J. P. Miller (Boston University, Boston, Massachusetts, USA), S. Miozzi (INFN, Sezione di Roma Tor Vergata, Rome, Italy), B. Mitra (33,w), J. P. Morgan (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), W. M. Morse (Brookhaven National Laboratory, Upton, New York, USA), J. Mott (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), A. Nath (9,e), J. K. Ng (20,21,d), H. Nguyen (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), Y. Oksuzian (Argonne National Laboratory, Lemont, Illinois, USA), Z. Omarov (Center for Axion and Precision Physics, Korea Advanced Institute of Science and Technology), W. Osar (Cornell University, Ithaca, New York, USA), R. Osofsky (University of Washington, Seattle, Washington, USA), S. Park (Center for Axion and Precision Physics), G. Pauletta (25,c), J. Peck (University of Kentucky, Lexington, Kentucky, USA), G. M. Piacentino (24,l), R. N. Pilato (University of Liverpool, Liverpool, United Kingdom), K. T. Pitts (27,x), B. Plaster (University of Kentucky, Lexington, Kentucky, USA), N. Pohlman (Northern Illinois University, DeKalb, Illinois, USA), C. C. Polly (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), D. Počanić (University of Virginia, Charlottesville, Virginia, USA), J. Price (University of Liverpool, Liverpool, United Kingdom), B. Quinn (University of Mississippi, University, Mississippi, USA), M. U. H. Qureshi (Institute of Physics and Cluster of Excellence PRISMA++, Johannes Gutenberg University Mainz, Mainz, Germany), G. Rakness (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), S. Ramachandran (1,k), E. Ramberg (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), R. Reimann (14,y), B. L. Roberts (Boston University, Boston, Massachusetts, USA), D. L. Rubin (Cornell University, Ithaca, New York, USA), M. Sakurai (Department of Physics and Astronomy, University College London, London, United Kingdom), L. Santi (25,c), C. Schlesier (27,z), A. Schreckenberger (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), Y. K. Semertzidis (5,15,aa), A. K. Soha (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), M. Sorbara (11,bb), J. Stapleton (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), D. Still (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), C. Stoughton (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), D. Stratakis (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), D. Stöckinger (Institut für Kern- und Teilchenphysik, Technische Universität Dresden, Dresden, Germany), H. E. Swanson (University of Washington, Seattle, Washington, USA), G. Sweetmore (Department of Physics and Astronomy, University of Manchester, Manchester, United Kingdom), D. A. Sweigart (Cornell University, Ithaca, New York, USA), M. J. Syphers (Northern Illinois University, DeKalb, Illinois, USA), Y. Takeuchi (20,21,d), D. A. Tarazona (Cornell University, Ithaca, New York, USA), T. Teubner (University of Liverpool, Liverpool, United Kingdom), A. E. Tewsley-Booth (University of Kentucky, Lexington, Kentucky, USA, University of Michigan, Ann Arbor, Michigan, USA), V. Tishchenko (Brookhaven National Laboratory, Upton, New York, USA), N. H. Tran (Boston University, Boston, Massachusetts, USA), W. Turner (University of Liverpool, Liverpool, United Kingdom), E. Valetov (16,cc), D. Vasilkova (University of Liverpool, Liverpool, United Kingdom), G. Venanzoni (29,dd), T. Walton (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), A. Weisskopf (Michigan State University, East Lansing, Michigan, USA), L. Welty-Rieger (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), P. Winter (Argonne National Laboratory, Lemont, Illinois, USA), Y. Wu (1,ee), B. Yu (University of Mississippi, University, Mississippi, USA), M. Yucel (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), E. Zaid (University of Liverpool, Liverpool, United Kingdom), Y. Zeng (20,21,d), C. Zhang (University of Liverpool, Liverpool, United Kingdom)

发布于 2026-08-12

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原作者： 2 Collaboration, D. P. Aguillard (University of Michigan, Ann Arbor, Michigan, USA), T. Albahri (University of Liverpool, Liverpool, United Kingdom), D. Allspach (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), J. Annala (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), K. Badgley (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), S. Baeßler (University of Virginia, Charlottesville, Virginia, USA), L. Bailey (Department of Physics and Astronomy, University College London, London, United Kingdom), E. Barlas-Yucel (27,a), T. Barrett (Cornell University, Ithaca, New York, USA), E. Barzi (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), F. Bedeschi (INFN, Sezione di Pisa, Pisa, Italy), M. Berz (Michigan State University, East Lansing, Michigan, USA), M. Bhattacharya (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), H. P. Binney (University of Washington, Seattle, Washington, USA), P. Bloom (North Central College, Naperville, Illinois, USA), J. Bono (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), E. Bottalico (University of Liverpool, Liverpool, United Kingdom), T. Bowcock (University of Liverpool, Liverpool, United Kingdom), S. Braun (University of Washington, Seattle, Washington, USA), M. Bressler (31,a), G. Cantatore (12,b), R. M. Carey (Boston University, Boston, Massachusetts, USA), B. C. K. Casey (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), D. Cauz (25,c), R. Chakraborty (University of Kentucky, Lexington, Kentucky, USA), A. Chapelain (Cornell University, Ithaca, New York, USA), S. Chappa (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), S. Charity (University of Liverpool, Liverpool, United Kingdom), C. Chen (20,21,d), M. Cheng (University of Illinois at Urbana-Champaign, Urbana, Illinois, USA), R. Chislett (Department of Physics and Astronomy, University College London, London, United Kingdom), Z. Chu (20,d), T. E. Chupp (University of Michigan, Ann Arbor, Michigan, USA), C. Claessens (University of Washington, Seattle, Washington, USA), F. Confortini (9,e), M. E. Convery (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), S. Corrodi (Argonne National Laboratory, Lemont, Illinois, USA), L. Cotrozzi (University of Liverpool, Liverpool, United Kingdom), J. D. Crnkovic (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), S. Dabagov (8,f), P. T. Debevec (University of Illinois at Urbana-Champaign, Urbana, Illinois, USA), S. Di Falco (INFN, Sezione di Pisa, Pisa, Italy), G. Di Sciascio (INFN, Sezione di Roma Tor Vergata, Rome, Italy), S. Donati (10,g), B. Drendel (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), A. Driutti (INFN, Sezione di Pisa, Pisa, Italy, University of Kentucky, Lexington, Kentucky, USA), M. Eads (Northern Illinois University, DeKalb, Illinois, USA), A. Edmonds (Boston University, Boston, Massachusetts, USA, City University of New York at York College, Jamaica, New York, USA), J. Esquivel (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), M. Farooq (University of Michigan, Ann Arbor, Michigan, USA), R. Fatemi (University of Kentucky, Lexington, Kentucky, USA), K. Ferraby (University of Liverpool, Liverpool, United Kingdom), C. Ferrari (10,h), M. Fertl (Institute of Physics and Cluster of Excellence PRISMA++, Johannes Gutenberg University Mainz, Mainz, Germany), A. T. Fienberg (University of Washington, Seattle, Washington, USA), A. Fioretti (10,h), D. Flay (Department of Physics, University of Massachusetts, Amherst, Massachusetts, USA), S. B. Foster (2,28,i), H. Friedsam (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), N. S. Froemming (18,j), C. Gabbanini (10,h), I. Gaines (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), S. Ganguly (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), J. George (31,k), L. K. Gibbons (Cornell University, Ithaca, New York, USA), A. Gioiosa (24,l), K. L. Giovanetti (Department of Physics and Astronomy, James Madison University, Harrisonburg, Virginia, USA), P. Girotti (10,m), W. Gohn (University of Kentucky, Lexington, Kentucky, USA), L. Goodenough (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), T. Gorringe (University of Kentucky, Lexington, Kentucky, USA), J. Grange (University of Michigan, Ann Arbor, Michigan, USA), S. Grant (Argonne National Laboratory, Lemont, Illinois, USA, Department of Physics and Astronomy, University College London, London, United Kingdom), F. Gray (19,n), S. Haciomeroglu (5,o), T. Halewood-Leagas (University of Liverpool, Liverpool, United Kingdom), D. Hampai (INFN, Laboratori Nazionali di Frascati, Frascati, Italy), F. Han (University of Kentucky, Lexington, Kentucky, USA), J. Hempstead (University of Washington, Seattle, Washington, USA), D. W. Hertzog (University of Washington, Seattle, Washington, USA), G. Hesketh (Department of Physics and Astronomy, University College London, London, United Kingdom), E. Hess (10,p), A. Hibbert (University of Liverpool, Liverpool, United Kingdom), Z. Hodge (University of Washington, Seattle, Washington, USA), S. Y. Hoh (20,21,q), K. W. Hong (University of Virginia, Charlottesville, Virginia, USA), R. Hong (Argonne National Laboratory, Lemont, Illinois, USA, University of Kentucky, Lexington, Kentucky, USA), T. Hu (20,21,d), Y. Hu (20,d), M. Iacovacci (9,e), M. Incagli (INFN, Sezione di Pisa, Pisa, Italy), S. Israel (Boston University, Boston, Massachusetts, USA, Department of Physics, University of Massachusetts, Amherst, Massachusetts, USA), P. Kammel (University of Washington, Seattle, Washington, USA), M. Kargiantoulakis (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), M. Karuza (12,p), J. Kaspar (University of Washington, Seattle, Washington, USA), D. Kawall (Department of Physics, University of Massachusetts, Amherst, Massachusetts, USA), L. Kelton (Department of Physics and Astronomy, Trinity University, San Antonio, Texas, USA, University of Kentucky, Lexington, Kentucky, USA), A. Keshavarzi (Department of Physics and Astronomy, University College London, London, United Kingdom), D. S. Kessler (Department of Physics, University of Massachusetts, Amherst, Massachusetts, USA), K. S. Khaw (20,21,d), Z. Khechadoorian (Cornell University, Ithaca, New York, USA), B. Kiburg (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), M. Kiburg (Fermi National Accelerator Laboratory, Batavia, Illinois, USA, North Central College, Naperville, Illinois, USA), O. Kim (33,n), N. Kinnaird (Boston University, Boston, Massachusetts, USA), E. Kraegeloh (University of Michigan, Ann Arbor, Michigan, USA), J. LaBounty (University of Washington, Seattle, Washington, USA), K. R. Labe (Cornell University, Ithaca, New York, USA), M. Lancaster (Department of Physics and Astronomy, University of Manchester, Manchester, United Kingdom), S. Lee (Center for Axion and Precision Physics), B. Li (20,r), D. Li (20,s), L. Li (20,d), I. Logashenko (4,t), A. Lorente Campos (University of Kentucky, Lexington, Kentucky, USA), Z. Lu (20,d), A. Lucà (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), G. Lukicov (Department of Physics and Astronomy, University College London, London, United Kingdom), A. Lusiani (10,u), A. L. Lyon (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), B. MacCoy (University of Washington, Seattle, Washington, USA), R. Madrak (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), K. Makino (Michigan State University, East Lansing, Michigan, USA), S. Mastroianni (INFN, Sezione di Napoli, Naples, Italy), R. McCarthy (2,v), J. P. Miller (Boston University, Boston, Massachusetts, USA), S. Miozzi (INFN, Sezione di Roma Tor Vergata, Rome, Italy), B. Mitra (33,w), J. P. Morgan (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), W. M. Morse (Brookhaven National Laboratory, Upton, New York, USA), J. Mott (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), A. Nath (9,e), J. K. Ng (20,21,d), H. Nguyen (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), Y. Oksuzian (Argonne National Laboratory, Lemont, Illinois, USA), Z. Omarov (Center for Axion and Precision Physics, Korea Advanced Institute of Science and Technology), W. Osar (Cornell University, Ithaca, New York, USA), R. Osofsky (University of Washington, Seattle, Washington, USA), S. Park (Center for Axion and Precision Physics), G. Pauletta (25,c), J. Peck (University of Kentucky, Lexington, Kentucky, USA), G. M. Piacentino (24,l), R. N. Pilato (University of Liverpool, Liverpool, United Kingdom), K. T. Pitts (27,x), B. Plaster (University of Kentucky, Lexington, Kentucky, USA), N. Pohlman (Northern Illinois University, DeKalb, Illinois, USA), C. C. Polly (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), D. Počanić (University of Virginia, Charlottesville, Virginia, USA), J. Price (University of Liverpool, Liverpool, United Kingdom), B. Quinn (University of Mississippi, University, Mississippi, USA), M. U. H. Qureshi (Institute of Physics and Cluster of Excellence PRISMA++, Johannes Gutenberg University Mainz, Mainz, Germany), G. Rakness (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), S. Ramachandran (1,k), E. Ramberg (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), R. Reimann (14,y), B. L. Roberts (Boston University, Boston, Massachusetts, USA), D. L. Rubin (Cornell University, Ithaca, New York, USA), M. Sakurai (Department of Physics and Astronomy, University College London, London, United Kingdom), L. Santi (25,c), C. Schlesier (27,z), A. Schreckenberger (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), Y. K. Semertzidis (5,15,aa), A. K. Soha (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), M. Sorbara (11,bb), J. Stapleton (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), D. Still (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), C. Stoughton (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), D. Stratakis (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), D. Stöckinger (Institut für Kern- und Teilchenphysik, Technische Universität Dresden, Dresden, Germany), H. E. Swanson (University of Washington, Seattle, Washington, USA), G. Sweetmore (Department of Physics and Astronomy, University of Manchester, Manchester, United Kingdom), D. A. Sweigart (Cornell University, Ithaca, New York, USA), M. J. Syphers (Northern Illinois University, DeKalb, Illinois, USA), Y. Takeuchi (20,21,d), D. A. Tarazona (Cornell University, Ithaca, New York, USA), T. Teubner (University of Liverpool, Liverpool, United Kingdom), A. E. Tewsley-Booth (University of Kentucky, Lexington, Kentucky, USA, University of Michigan, Ann Arbor, Michigan, USA), V. Tishchenko (Brookhaven National Laboratory, Upton, New York, USA), N. H. Tran (Boston University, Boston, Massachusetts, USA), W. Turner (University of Liverpool, Liverpool, United Kingdom), E. Valetov (16,cc), D. Vasilkova (University of Liverpool, Liverpool, United Kingdom), G. Venanzoni (29,dd), T. Walton (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), A. Weisskopf (Michigan State University, East Lansing, Michigan, USA), L. Welty-Rieger (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), P. Winter (Argonne National Laboratory, Lemont, Illinois, USA), Y. Wu (1,ee), B. Yu (University of Mississippi, University, Mississippi, USA), M. Yucel (Fermi National Accelerator Laboratory, Batavia, Illinois, USA), E. Zaid (University of Liverpool, Liverpool, United Kingdom), Y. Zeng (20,21,d), C. Zhang (University of Liverpool, Liverpool, United Kingdom)

原始论文采用 CC BY 4.0 许可（http://creativecommons.org/licenses/by/4.0/）。 ✨ 这是对下方论文的AI生成解释。它不是由作者撰写或认可的。如需技术准确性，请参阅原始论文。阅读完整免责声明

宇宙侦探故事：寻找微小的倾斜

想象一下，宇宙是一个巨大的、隐形的舞池，每一个粒子都有其独特的节奏。几十年来，物理学家一直试图弄清楚为什么宇宙主要由物质组成，而反物质却极少。根据我们现有的最完善规则（标准模型），物质和反物质应该以相等的量被创造出来，然后互相湮灭，最后什么都不剩。但我们现在确实存在，所以一定有什么东西打破了这种平衡。

为了找到元凶，科学家们在寻找“对称性破缺”。想象一个完美的旋转陀螺。如果它垂直旋转，从任何角度看都一样。但如果它摇晃或倾斜，对称性就被打破了。在亚原子粒子的世界里，粒子有两种主要的“摇晃”方式：它可以具有磁偶极矩（就像一个小型的条形磁铁）或者电偶极矩（EDM）。磁性的就像指南针针尖；我们知道它的存在。然而，电性的则是机器中的幽灵。如果一个粒子具有电偶极矩，这意味着它的正电荷和负电荷略微分离，产生了一个微小的电“倾斜”，这违反了时间与空间的对称性规则。发现这种倾斜，就像是发现了宇宙配方中的秘密成分，解释了我们为何存在。但到目前为止，这种成分极其难以寻觅，隐藏在我们最灵敏实验的阴影之中。

寻找隐形的倾斜

在这场狩猎的最新篇章中，费米实验室（Fermilab）的 Muon g-2 合作组对缪子（muon）进行了全新的观察，它是电子的一个重质量“表亲”。他们想看看缪子是否具有这种难以捉摸的电偶极矩。把缪子想象成一个在巨大的磁性赛道内高速旋转的微型超高速陀螺。当它疾驰时，它的自旋通常会在一个可预测的水平圆周内摇摆，就像在桌面上进动旋转的陀螺一样。

团队的大构思既简单又巧妙：如果缪子具有电偶极矩，实验室内的电场力就会推挤它的“电荷分离”，导致其自旋轴稍微向上或向下倾斜，偏离平坦的赛道。这就像你在桌上旋转一个陀螺，有人从侧面轻轻吹了一口气，导致陀螺向一侧倾斜。研究人员并不是直接寻找这种倾斜，而是观察缪子衰变为正电子（反电子）的过程。由于缪子衰变的方式，正电子会相对于缪子的自旋向特定方向射出。如果自旋发生了倾斜，正电子平均飞出的垂直角度会比预期稍有不同。

团队分析了 2019 年和 2020 年的数据，追踪了数十亿次这类衰变事件。他们使用了一套特殊的“秸秆探测器（straw trackers）”——本质上是一圈中空管，像高科技眼睛一样捕捉正电子并以惊人的精度测量它们的路径。通过测量这些正电子随时间变化的平均垂直角度，他们可以观察是否存在与电偶极矩特征相吻合的有节奏的摇摆。

结果：一个非常平坦的自旋

在处理完数据并经过严格的过程以确保没有隐藏误差干扰结果后，答案出来了：缪子并没有倾斜。数据显示，正电子的平均垂直角度与零倾斜是一致的。测得的缪子电偶极矩值为 $d_\mu = (-0.35 \pm 0.19_{\text{stat}} \pm 0.34_{\text{sys}}) \times 10^{-19} \text{ e}\cdot\text{cm}$ 。

由于这个数值如此接近于零，且不确定度范围包含了零，团队得出结论：他们并未发现永久性的电偶极矩。相反，他们设定了一个更严格的新限值，规定了它可能存在的最大程度。他们指出，在 95% 的置信度下，缪子的电偶极矩小于 $1.10 \times 10^{-19} \text{ e}\cdot\text{cm}$ 。

这是一个显著的进步，相比之前来自布鲁克海文国家实验室（Brookhaven National Laboratory）的最佳限值，它将搜索网收紧了 1.5 倍。虽然这一结果并未揭示解释物质-反物质失衡的“秘密成分”，但它排除了许多预测存在较大倾斜的理论。作者指出，这一结果受限于系统不确定性——具体而言，是追踪探测器的对准精度。他们预计，随着未来运行数据的增加，他们将能够更完美地对准探测器，从而进一步降低这一限值，继续寻找那微小到足以定义宇宙的摇摆。

技术摘要：改进的缪子电偶极矩直接极限

问题与动机
观测到的宇宙物质-反物质不对称性无法通过标准模型（SM）内已知的电荷-宇称（CP）破坏来源来解释 [1, 2]。电偶极矩（EDM）违反了宇称（P）和时间反演（T）对称性；在假设 CPT 守恒的前提下，非零的 EDM 意味着 CP 破坏。尽管目前尚未观测到任何基本粒子或束缚态（如中子）具有 EDM [3–5]，但标准模型对缪子 EDM 的预测极小（ $O(10^{-38})$ e·cm）[6]。源自电子 EDM 测量或原子核中缪子环路相互作用的间接极限依赖于某些假设（例如最小 flavor 违规），而这些假设在超越标准模型（BSM）的物理学中可能并不成立 [7–10]。因此，对缪子 EDM 进行直接测量至关重要。若结果在当前实验极限附近与零不一致，将矛盾于标准模型并对 BSM 理论构成约束 [13, 14]。

方法论
本分析利用了费米实验室（Fermilab）缪子 $g-2$ 实验在 2019 年至 2020 年间收集的数据（Run-2, Run-3a, 和 Run-3b）。该实验采用注入到 1.45 T 超导磁场存储环中的高度极化正缪子束流，其“魔力动量”（magic momentum）为 3.094 GeV/c，在此动量下，电场贡献导致的自旋进动消失。

测量原理： 在存在非零 EDM ( $d_\mu$ ) 的情况下，会产生一个作用于缪子自旋的转矩，使自旋进动平面偏离水平面。这种倾斜（ $\delta$ ）会在缪子衰变产生的正电子平均垂直衰变角（ $\langle \theta_y \rangle$ ）中诱发振荡。该振荡发生的频率为反常进动频率（ $\omega_a$ ），且与标准的自旋进动振荡相位差为 $\pi/2$ 。
探测： 分析依赖于真空内秸秆式径迹器站（S12 和 S18）来测量衰变正电子的轨迹。数据集包含在特定时间窗口内（注入后 26.2 至 602.4 $\mu$ s）探测到的 $2.34 \times 10^9$ 个正电子。
分析策略： $\langle \theta_y \rangle$ 按进动周期进行分箱处理。数据被拟合为一个包含相对于反常进动的同相（ $C_a$ ）和异相（ $S_a$ ）分量的函数。振幅 $S_a$ 与 EDM 直接成正比。
修正与系统误差：
- R-因子： 测得的振幅需经过洛伦兹增益（ $R_\gamma$ ）、束流极化（ $R_P$ ）、动量相关衰变角展宽（ $R_{e^+}$ ）以及探测器接受度（ $R_{acc}$ ）的修正。
- 盲分析： 分析通过注入一个未知的振荡信号进行了盲化处理。初步的“软解盲”检查显示出差异，促使进行了内部审查，从而确定了径迹器的垂直失准以及纵向磁场的确定性问题。
- 类 EDM 信号： 针对由径迹器垂直失准（改变平均垂直位置）和径向磁场分量（导致静止系倾斜）引起的伪信号进行了修正。同时使用纵向磁场测量值来分配不确定度。

主要贡献与结果
本文通过对 48 个独立测量（涵盖三个运行阶段、两个站点和八个动量分量）的综合分析，提出了一个新的直接的缪子 EDM 极限。

最终结果： 综合测量得到的缪子 EDM 为：
$d_\mu = (-0.35 \pm 0.19_{\text{stat}} \pm 0.34_{\text{sys}}) \times 10^{-19} \text{ e}\cdot\text{cm}$
该结果与零一致。
极限值： 基于 Feldman-Cousins 程序，本文给出了单侧上限：
$|d_\mu| < 1.10 \times 10^{-19} \text{ e}\cdot\text{cm} \quad \text{置信水平为 95\%}$
$|d_\mu| < 0.98 \times 10^{-19} \text{ e}\cdot\text{cm} \quad \text{置信水平为 90\%}$
不确定度分解： 结果受系统误差限制。最主要的系统误差来源（3.12 $\times 10^{-20}$ e·cm）来自于径迹器垂直对准的修正。其他显著贡献包括径迹重建对准以及束流动力学与接受度的耦合。统计不确定度为 1.87 $\times 10^{-20}$ e·cm。
对比： 本次结果的总不确定度比之前布鲁克海文国家实验室（BNL E821）实验的最佳直接极限（ $|d_\mu| < 1.8 \times 10^{-19} \text{ e}\cdot\text{cm}$ ）小了一个因子 2.3。

意义
论文声称，这一结果设定了新的直接缪子 EDM 极限，将此前 95% 置信水平的极限提高了 1.5 倍。作者指出，当前结果受限于系统误差，特别是垂直对准的确定。他们表示，该不确定度在统计上是受限的，并且预计在包含未来运行阶段（Run 4, 5, 和 6）的完整数据集时将得到显著改善，届时将提供比本次分析多出 2.5 倍的统计量。该测量结果仍与标准模型预测一致，并为 BSM 理论提供了严格的约束。

宇宙侦探故事：寻找微小的倾斜

寻找隐形的倾斜

结果：一个非常平坦的自旋

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