Recent progress of laser spectroscopy experiments on antiprotonic helium

• Published in: Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences Vol. 376; no. 2116; pp. 1 - 8
• Main Author: Hori, Masaki
• Format: Journal Article
• Language: English
• Published: THE ROYAL SOCIETY 28.03.2018
• ISSN: 1364-503X; 1471-2962

The Atomic Spectroscopy and Collisions Using Slow Antiprotons (ASACUSA) collaboration is currently carrying out laser spectroscopy experiments on antiprotonic helium (p̅He⁺ = p̅ + He²⁺ + e⁻) atoms at CERN's Antiproton Decelerator facility. Two-photon spectroscopic techniques have been employed to reduce the Doppler width of the measured p̅He⁺ resonance lines, and determine the atomic transition frequencies to a fractional precision of 2.3–5 parts in 10⁹. More recently, single-photon spectroscopy of buffer-gas cooled p̅He⁺ has reached a similar precision. By comparing the results with threebody quantum electrodynamics calculations, the antiproton-to-electron mass ratio was determined as Mp̅/me = 1836.1526734(15), which agrees with the known proton-to-electron mass ratio with a precision of 8 × 10⁻¹⁰. The high-quality antiproton beam provided by the future Extra Low Energy Antiproton Ring (ELENA) facility should enable further improvements in the experimental precision. This article is part of the Theo Murphy meeting issue 'Antiproton physics in the ELENA era'.