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Ahmadi M, Alves BXR, Baker CJ, Bertsche W, Capra A, Carruth C, Cesar CL, Charlton M, Cohen S, Collister R, Eriksson S, Evans A, Evetts N, Fajans J, Friesen T, Fujiwara MC, Gill DR, Granum P, Hangst JS, Hardy WN, Hayden ME, Hunter ED, Isaac CA, Johnson MA, Jones JM, Jones SA, Jonsell S, Khramov A, Knapp P, Kurchaninov L, Madsen N, Maxwell D, McKenna JTK, Menary S, Michan JM, Momose T, Munich JJ, Olchanski K, Olin A, Pusa P, Rasmussen CØ, Robicheaux F, Sacramento RL, Sameed M, Sarid E, Silveira DM, So C, Starko DM, Stutter G, Tharp TD, Thompson RI, van der Werf DP, Wurtele JS. Investigation of the fine structure of antihydrogen. Nature 2020; 578:375-380. [PMID: 32076225 PMCID: PMC7162817 DOI: 10.1038/s41586-020-2006-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Accepted: 12/20/2019] [Indexed: 10/29/2022]
Abstract
At the historic Shelter Island Conference on the Foundations of Quantum Mechanics in 1947, Willis Lamb reported an unexpected feature in the fine structure of atomic hydrogen: a separation of the 2S1/2 and 2P1/2 states1. The observation of this separation, now known as the Lamb shift, marked an important event in the evolution of modern physics, inspiring others to develop the theory of quantum electrodynamics2-5. Quantum electrodynamics also describes antimatter, but it has only recently become possible to synthesize and trap atomic antimatter to probe its structure. Mirroring the historical development of quantum atomic physics in the twentieth century, modern measurements on anti-atoms represent a unique approach for testing quantum electrodynamics and the foundational symmetries of the standard model. Here we report measurements of the fine structure in the n = 2 states of antihydrogen, the antimatter counterpart of the hydrogen atom. Using optical excitation of the 1S-2P Lyman-α transitions in antihydrogen6, we determine their frequencies in a magnetic field of 1 tesla to a precision of 16 parts per billion. Assuming the standard Zeeman and hyperfine interactions, we infer the zero-field fine-structure splitting (2P1/2-2P3/2) in antihydrogen. The resulting value is consistent with the predictions of quantum electrodynamics to a precision of 2 per cent. Using our previously measured value of the 1S-2S transition frequency6,7, we find that the classic Lamb shift in antihydrogen (2S1/2-2P1/2 splitting at zero field) is consistent with theory at a level of 11 per cent. Our observations represent an important step towards precision measurements of the fine structure and the Lamb shift in the antihydrogen spectrum as tests of the charge-parity-time symmetry8 and towards the determination of other fundamental quantities, such as the antiproton charge radius9,10, in this antimatter system.
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Bertsche WA. Prospects for comparison of matter and antimatter gravitation with ALPHA-g. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2018; 376:20170265. [PMID: 29459415 PMCID: PMC5829170 DOI: 10.1098/rsta.2017.0265] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Accepted: 11/24/2017] [Indexed: 06/08/2023]
Abstract
The ALPHA experiment has recently entered an expansion phase of its experimental programme, driven in part by the expected benefits of conducting experiments in the framework of the new AD + ELENA antiproton facility at CERN. With antihydrogen trapping now a routine operation in the ALPHA experiment, the collaboration is leading progress towards precision atomic measurements on trapped antihydrogen atoms, with the first excitation of the 1S-2S transition and the first measurement of the antihydrogen hyperfine spectrum (Ahmadi et al. 2017 Nature541, 506-510 (doi:10.1038/nature21040); Nature548, 66-69 (doi:10.1038/nature23446)). We are building on these successes to extend our physics programme to include a measurement of antimatter gravitation. We plan to expand a proof-of-principle method (Amole et al. 2013 Nat. Commun.4, 1785 (doi:10.1038/ncomms2787)), first demonstrated in the original ALPHA apparatus, and perform a precise measurement of antimatter gravitational acceleration with the aim of achieving a test of the weak equivalence principle at the 1% level. The design of this apparatus has drawn from a growing body of experience on the simulation and verification of antihydrogen orbits confined within magnetic-minimum atom traps. The new experiment, ALPHA-g, will be an additional atom-trapping apparatus located at the ALPHA experiment with the intention of measuring antihydrogen gravitation.This article is part of the Theo Murphy meeting issue 'Antiproton physics in the ELENA era'.
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Affiliation(s)
- W A Bertsche
- University of Manchester, School of Physics and Astronomy, Oxford Road, Manchester M13 9PL, UK
- The Cockcroft Institute, Keckwick Lane, Daresbury, Warrington WA4 4AD, UK
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Madsen N. Antiproton physics in the ELENA era. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2018; 376:rsta.2017.0278. [PMID: 29459419 PMCID: PMC5829179 DOI: 10.1098/rsta.2017.0278] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 12/13/2017] [Indexed: 06/08/2023]
Affiliation(s)
- N Madsen
- Department of Physics, Swansea University, Singleton Park, Swansea SA2 8PP, UK
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