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Trapped antihydrogen



Antimatter was first predicted1 in 1931, by Dirac. Work with high-energy antiparticles is now commonplace, and anti-electrons are used regularly in the medical technique of positron emission tomography scanning. Antihydrogen, the bound state of an antiproton and a positron, has been produced2,3 at low energies at CERN (the European Organization for Nuclear Research) since 2002. Antihydrogen is of interest for use in a precision test of nature’s fundamental symmetries. The charge conjugation/parity/time reversal (CPT) theorem, a crucial part of the foundation of the standard model of elementary particles and interactions, demands that hydrogen and antihydrogen have the same spectrum. Given the current experimental precision of measurements on the hydrogen atom (about two parts in 1014 for the frequency of the 1s-to-2s transition4), subjecting antihydrogen to rigorous spectroscopic examination would constitute a compelling, model-independent test of CPT. Antihydrogen could also be used to study the gravitational behaviour of antimatter5. However, so far experiments have produced antihydrogen that is not confined, precluding detailed study of its structure. Here we demonstrate trapping of antihydrogen atoms. From the interaction of about 107 antiprotons and 7 × 108 positrons, we observed 38 annihilation events consistent with the controlled release of trapped antihydrogen from our magnetic trap; the measured background is 1.4 ± 1.4 events. This result opens the door to precision measurements on anti-atoms, which can soon be subjected to the same techniques as developed for hydrogen.

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Figure 1: The ALPHA central apparatus and mixing potential.
Figure 2: Detected antiproton annihilation and cosmic ray events.
Figure 3: Distributions of released antihydrogen atoms and antiprotons.


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This work was supported by CNPq, FINEP/RENAFAE (Brazil); ISF (Israel); MEXT (Japan); FNU (Denmark); VR (Sweden); NSERC, NRC/TRIUMF, AIF, FQRNT (Canada); the DOE and the NSF (USA); and EPSRC, the Royal Society and the Leverhulme Trust (UK). We thank them for their generous support. We are grateful to the Antiproton Decelerator team, T. Eriksson, P. Belochitskii, B. Dupuy, L. Bojtar, C. Oliveira, K. Mikluha and G. Tranquille, for the delivery of a high-quality antiproton beam. The contributions of summer students C. C. Bray, C. Ø. Rasmussen, S. Kemp, K. K. Andersen, D. Wilding, K. Mikkelsen and L. Bryngemark are acknowledged. We would like to thank the following individuals for help: M. Harrison, J. Escallier, A. Marone, M. Anerella, A. Ghosh, B. Parker, G. Ganetis, J. Thornhill, D. Wells, D. Seddon, K. Dahlerup-Pedersen, J. Mourao, T. Fowler, S. Russenschuck, R. De Oliveira, N. Wauquier, J. Hansen, M. Polini, J. M. Geisser, L. Deparis, P. Frichot, J. M. Malzacker, A. Briswalter, P. Moyret, S. Mathot, G. Favre, J. P. Brachet, P. Mésenge, S. Sgobba, A. Cherif, J. Bremer, J. Casas-Cubillos, N. Vauthier, G. Perinic, O. Pirotte, A. Perin, G. Perinic, B. Vullierme, D. Delkaris, N. Veillet, K. Barth, R. Consentino, S. Guido, L. Stewart, M. Malabaila, A. Mongelluzzo, P. Chiggiato, E. Mahner, A. Froton, C. Lasseur, F. Hahn, E. Søndergaard, F. Mikkelsen, W. Carlisle, A. Charman, J. Keller, P. Amaudruz, D. Bishop, R. Bula, K. Langton, P. Vincent, S. Chan, D. Rowbotham, P. Bennet, B. Evans, J.-P. Martin, P. Kowalski, A. Read, T. Willis, J. Kivell, H. Thomas, W. Lai, L. Wasilenko, C. Kolbeck, H. Malik, P. Genoa, L. Posada and R. Funakoshi.

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W.B., P.D.B., J.F., M.C.F., J.S.H., N.M. and D.M.S. conceived, designed and constructed the central ALPHA apparatus and participated in all aspects of the experimental and physics programmes. G.B.A., M.D.A., M.B.-R., E.B., S.C., T.F., A.J.H., R.H., M.J.J., A.P., S.S.e.N. and C.S. participated actively in the experimental runs, data taking, on- and offline analysis, and maintenance and modification of the apparatus. D.R.G., A.O. and J.W.S. contributed to all aspects of the detector systems and participated actively in the experimental and analysis efforts. M.C., D.P.v.d.W. and L.V.J. designed and built the positron accumulator and participated in the experimental programme. F.R. performed the particle simulations reported in this paper, made the theoretical estimate of trapping rate and supported the design and experimental programmes with simulations and calculations. P.N. led the design of the ALPHA silicon detector. P.P. was responsible for implementing the silicon detector at CERN and participated in the experimental and analysis programmes. A.D. and A.G. contributed to the experimental shift work. S.J. and J.S.W. contributed theoretical support in the form of atomic or plasma physics calculations and simulations, and provided guidance in the experimental programme. E.S. contributed to the multichannel plate imaging system and participated in the experimental efforts. C.L.C., W.N.H., M.E.H., S.E., S.M. and R.I.T. participated in the experimental programme and the physics planning effort. Y.Y. provided organizational and financial support and participated in physics discussions. L.K. and K.O. provided off-site support for detector electronics and database management systems, respectively. J.S.H. wrote the initial manuscript, which was edited by J.F., M.C.F., P.D.B., N.M. and E.B. before being improved and approved by the entire collaboration.

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Correspondence to J. S. Hangst.

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Andresen, G., Ashkezari, M., Baquero-Ruiz, M. et al. Trapped antihydrogen. Nature 468, 673–676 (2010).

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