Abstract
The goal of the ASACUSA-CUSP collaboration at the Antiproton Decelerator of CERN is to measure the ground-state hyperfine splitting of antihydrogen using an atomic spectroscopy beamline. A milestone was achieved in 2012 through the detection of 80 antihydrogen atoms 2.7 m away from their production region. This was the first observation of ‘cold’ antihydrogen in a magnetic field free region. In parallel to the progress on the antihydrogen production, the spectroscopy beamline was tested with a source of hydrogen. This led to a measurement at a relative precision of 2.7×10−9 which constitutes the most precise measurement of the hydrogen hyperfine splitting in a beam. Further measurements with an upgraded hydrogen apparatus are motivated by CPT and Lorentz violation tests in the framework of the Standard Model Extension. Unlike for hydrogen, the antihydrogen experiment is complicated by the difficulty of synthesizing enough cold antiatoms in the ground state. The first antihydrogen quantum states scan at the entrance of the spectroscopy apparatus was realized in 2016 and is presented here. The prospects for a ppm measurement are also discussed.This article is part of the Theo Murphy meeting issue ‘Antiproton physics in the ELENA era’.
Highlights
Since the first detection of relativistic antihydrogen atoms more than 20 years ago at LEAR (CERN) [1] and later at Fermilab [2], the field of antihydrogen research rapidly took momentum with the start of the Antiproton Decelerator (AD) at CERN in 2000
The race towards producing large amount of cold antihydrogen atoms is motivated by the appealing prospects for CPT symmetry tests
The Extra Low Energy Antiproton Ring ELENA [54] which is being commissioned at the AD, will provide, starting from 2021 for the majority of antihydrogen experiments, a lower beam energy and a higher beam availability which will be beneficial to the ASACUSA-CUSP
Summary
Since the first detection of relativistic antihydrogen atoms more than 20 years ago at LEAR (CERN) [1] and later at Fermilab [2], the field of antihydrogen research rapidly took momentum with the start of the Antiproton Decelerator (AD) at CERN in 2000. Given the current knowledge on the magnetic moment of the antiproton, the ground-state hyperfine splitting of antihydrogen is sensitive at the 30 ppm level to the structure of the antiproton This strongly motivates, in addition to the prospect for more sensitive CPT tests, further experiments beyond the currently achieved relative precision of 4 × 10−4 in a trap. In hydrogen additional constraints on SME coefficients can be obtained by measuring sidereal variations of the hyperfine splitting which could be caused by the change of the magnetic field orientation (due to the rotation of the Earth) with respect to the background fields responsible for Lorentz violation. The spectroscopy apparatus (a resonant cavity in which the hyperfine transition is driven and a superconducting sextupole magnet to select the spin state) designed for the ASACUSA-CUSP antihydrogen experiment (see §3a) was used for this measurement. It is worth noting that the hydrogen experiment is located at the same Earth’s latitude and longitude coordinates as our analogue antihydrogen experiment
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