A theoretical underpinning of the standard model of fundamental particles and interactions is CPT invariance, which requires that the laws of physics be invariant under the combined discrete operations of charge conjugation, parity and time reversal. Antimatter, the existence of which was predicted by Dirac, can be used to test the CPT theorem—experimental investigations involving comparisons of particles with antiparticles are numerous1. Cold atoms and anti-atoms, such as hydrogen and antihydrogen, could form the basis of a new precise test, as CPT invariance implies that they must have the same spectrum. Observations of antihydrogen in small quantities and at high energies have been reported at the European Organization for Nuclear Research (CERN)2 and at Fermilab3, but these experiments were not suited to precision comparison measurements. Here we demonstrate the production of antihydrogen atoms at very low energy by mixing trapped antiprotons and positrons in a cryogenic environment. The neutral anti-atoms have been detected directly when they escape the trap and annihilate, producing a characteristic signature in an imaging particle detector.
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The authors comprise the ATHENA Collaboration. We would like to thank G. Bendiscioli, S. Bricola, P. Chiggiato, J. Hansen, H. Higaki, A. Lanza, C. Marciano, O. Meshkov, P. Salvini, G. Sobrero, B. Schmid and E. Søndergaard. We also thank the CERN AD team and C. Surko, who provided essential advice. This work was supported by Istituto Nazionale di Fisica Nucleare (Italy), Conselho Nacional de Desenvolvimento Científico e Technológico, Fundação de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ) e Fundação CCMN/UFRJ (Brazil), Grant-in-Aid for Creative Basic Research of Monbukagakusho (Japan), the Swiss National Science Foundation, the Danish Natural Science Research Council, The UK Engineering and Physical Sciences Research Council (EPSRC), The EU (Eurotraps Network), and the Royal Society. L.V.J., M.H.H., M.C. and J.S.H. acknowledge the work of the late B. Deutch.
The authors declare that they have no competing financial interests.
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Amoretti, M., Amsler, C., Bonomi, G. et al. Production and detection of cold antihydrogen atoms. Nature 419, 456–459 (2002). https://doi.org/10.1038/nature01096
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