Recent progress of laser spectroscopy experiments on antiprotonic helium

Abstract

The Atomic Spectroscopy and Collisions Using Slow Antiprotons (ASACUSA) collaboration is currently carrying out laser spectroscopy experiments on antiprotonic helium [Formula: see text] atoms at CERN's Antiproton Decelerator facility. Two-photon spectroscopic techniques have been employed to reduce the Doppler width of the measured [Formula: see text] resonance lines, and determine the atomic transition frequencies to a fractional precision of 2.3-5 parts in 10 More recently, single-photon spectroscopy of buffer-gas cooled [Formula: see text] has reached a similar precision. By comparing the results with three-body quantum electrodynamics calculations, the antiproton-to-electron mass ratio was determined as [Formula: see text], which agrees with the known proton-to-electron mass ratio with a precision of 8×10 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'.

Antiproton physics in the ELENA era

“…So far, the AD has been host to eight different experiments (ACE [8], AEgIS [9], ALPHA [10,11], ASACUSA [12,13], ATHENA [14], ATRAP [15], BASE [16] and GBAR [17], and all but ACE and ATHENA are ongoing), that delve into the myriad of questions one can hope to answer using low-energy antiprotons. Thanks to a string of successes from the experiments (see the following articles in this volume for further details), CERN has decided, with help from the user community, to expand the facility in a remarkable way with development of the Extra Low Energy Antiproton (ELENA) facility [18].…”