Buffer-gas cooling of antiprotonic helium to 1.5 to 1.7 K, and antiproton-to-electron mass ratio

Masaki Hori, Hossein Aghai-Khozani, Anna Sótér, D. Barna, Andreas Dax, Ryugo Hayano, Takumi Kobayashi, Yohei Murakami, Koichi Todoroki, Hiroyuki Yamada, D. Horváth, Luca Venturelli

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Charge, parity, and time reversal (CPT) symmetry implies that a particle and its antiparticle have the same mass. The antiproton-to-electron mass ratio Mp=me can be precisely determined from the single-photon transition frequencies of antiprotonic helium. We measured 13 such frequencies with laser spectroscopy to a fractional precision of 2.5 × 10-9 to 16 × 10-9. About 2 × 109 antiprotonic helium atoms were cooled to temperatures between 1.5 and 1.7 kelvin by using buffer-gas cooling in cryogenic lowpressure helium gas; the narrow thermal distribution led to the observation of sharp spectral lines of small thermal Doppler width. The deviation between the experimental frequencies and the results of three-body quantum electrodynamics calculations was reduced by a factor of 1.4 to 10 compared with previous single-photon experiments. From this, Mp=me was determined as 1836.1526734(15), which agrees with a recent proton-toelectron experimental value within 8 × 10-10.

Original languageEnglish
Pages (from-to)610-614
Number of pages5
Issue number6312
Publication statusPublished - Nov 4 2016


ASJC Scopus subject areas

  • Medicine(all)
  • General

Cite this

Hori, M., Aghai-Khozani, H., Sótér, A., Barna, D., Dax, A., Hayano, R., Kobayashi, T., Murakami, Y., Todoroki, K., Yamada, H., Horváth, D., & Venturelli, L. (2016). Buffer-gas cooling of antiprotonic helium to 1.5 to 1.7 K, and antiproton-to-electron mass ratio. Science, 354(6312), 610-614. https://doi.org/10.1126/science.aaf6702