The laws of physics predict equal amounts of matter and antimatter in the primordial universe. However, our present universe consists almost entirely of matter. For scientists, this begs a question. Is there a slight asymmetry in the laws that govern matter and antimatter? Enabled by plasma physics research, scientists are studying this question by examining antihydrogen atoms—the antimatter equivalent of hydrogen. The team greatly improved the trapping rate of antihydrogen atoms and made the first measurements of antihydrogen spectrum, the characteristic color with which antihydrogen glows.
The challenges related to probing antihydrogen with laser light are extreme. Why? Antihydrogen does not occur naturally. Scientists must synthesize antihydrogen and judiciously protect it from interaction with atoms of regular matter—with which it will annihilate. In a major technological advance, scientists have developed new ways probe antimatter with laser light.
The big bang should have yielded equal amounts of matter and antimatter, yet observations suggest that there is very little antimatter in the universe. This conundrum, which is one of the most significant outstanding problems in the theory of the early universe, is called the baryogenesis problem. Physicists have explored many possibilities to account for this matter-antimatter imbalance, but without generally agreed upon success. A difference between the spectra of hydrogen and antihydrogen would require a violation of the deep symmetry principle (charge-parity-time invariance, or CPT). Such a violation might lead to a solution of the baryogenesis problem. To this end, the international ALPHA team at the European Organization for Nuclear Research (CERN) trapped nearly 500 antihydrogen atoms, illuminated these antiatoms with near 243 nm laser light, and searched for light-antiatom interactions that would lead to the detrapping or ionization. The resulting detrapped or ionized antiatoms can be detected readily. The antiatoms provide a signal when the illuminating light is of the correct wavelength. By using two different wavelengths, the physicists established that the antiatoms were interacting with the light at nearly the same wavelength as is found for normal-matter hydrogen, and point the way to obtaining a complete spectrum of antihydrogen.
The U.S. collaboration on ALPHA at the University of California, Berkeley, was supported by the U.S. Department of Energy, Office of Science, and the National Science Foundation. The international ALPHA collaboration is supported by the European Research Council Advanced Grant program; Ministry of Science, Technology, Innovation and Communications (CNPq), Carlos Chagas Filho Foundation for Research Support of the State of Rio de Janeiro (FAPERJ), National Network of High Energy Physics (RENAFAE) (Brazil); Natural Sciences and Engineering Research Council of Canada, National Research Council Canada/TRIUMF, Eyes High Post-Doctoral Scholarship/Eyes High Doctoral Recruitment Scholarship (EHPDS/EHDRS) programs (Canada), Research Fund: Nature and Technologies (FQRNT) (Canada); Forskningsrådet for Natur og Univers (FNU) (Nice project, Denmark), Carlsberg Foundation (Denmark); Japan Society for the Promotion of Science Postdoctoral Fellowships for Research Abroad (Japan); Israel Science Foundation (Israel); Science and Technology Facilities Council (STFC), Engineering and Physical Sciences Research Council (EPSRC), the Royal Society, and the Leverhulme Trust (UK); and Swedish Research Council (VR) (Sweden).
M. Ahmadi, B.X.R. Alves, C.J. Baker, W. Bertsche, E. Butler, A. Capra, C. Carruth, C.L. Cesar, M. Charlton, S. Cohen, R. Collister, S. Eriksson, A. Evans, N. Evetts, J. Fajans, T. Friesen, M.C. Fujiwara, D.R. Gill, A. Gutierrez, J.S. Hangst, W.N. Hardy, M.E. Hayden, C.A. Isaac, A. Ishida, M.A. Johnson, S.A. Jones, S. Jonsell, L. Kurchaninov, N. Madsen, M. Mathers, D. Maxwell, J.T.K. McKenna, S. Menary, J.M. Michan, T. Momose, J.J. Munich, P. Nolan, K. Olchanski, A. Olin, P. Pusa, C.Ø. Rasmussen, F. Robicheaux, R.L. Sacramento, M. Sameed, E. Sarid, D.M. Silveira, S. Stracka, G. Stutter, C. So, T.D. Tharp, J.E. Thompson, R.I. Thompson, D.P. van der Werf, and J.S. Wurtele, “Observation of the 1S–2S transition in trapped antihydrogen.” Nature 541, 506-510 (2016). [DOI: 10.1038/nature21040]