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

Collaboration
Nov 4, 2016
5 pages
Published in:
  • Science 354 (2016) 6312, 610-614
  • Published: Nov 4, 2016
Experiments:

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Abstract:
Charge, parity, and time reversal (CPT) symmetry implies that a particle and its antiparticle have the same mass. The antiproton-to-electron mass ratio Embedded Image 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 2.5×1092.5 × 10^{-9} to 16×10916 × 10^{-9}. About 2×1092 × 10^9 antiprotonic helium atoms were cooled to temperatures between 1.5 and 1.7 kelvin by using buffer-gas cooling in cryogenic low-pressure 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, Mpˉ/meM_{\bar{p}}/m_e was determined as 1836.1526734(15), which agrees with a recent proton-to-electron experimental value within 8×10108 × 10^{-10}.
  • anti-p
  • electron
  • mass ratio
  • transition: frequency
  • helium: gas
  • pressure: low
  • cryogenics
  • thermal
  • beam emittance
  • beam: pulsed
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