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In addition, the estimated precision of planned experiments is indicated in the figure. The zero-field value of ν ¯ ¯¯ ¯ H H F S was directly determined to δ ν = 4 × 10 − 4 using the difference of two microwave transitions. ![]() ν ¯ ¯¯ ¯ H 2 S − 2 P was determined to δ ν = 11% from the measured frequencies of ν ¯ ¯¯ ¯ H 1 S − 2 S and As the quantity measured is dominated by the electro-magnetic interaction, this makes the current result not a pure test of CPT which would require comparing ν H 1 S − 2 S and ν ¯ ¯¯ ¯ H 1 S − 2 S at the same magnetic field. 1: ν ¯ ¯¯ ¯ H 1 S − 2 S was measured to δ ν = 2 × 10 − 12, although the measurement is taken in a background magnetic field of B = 1.033 T and compared to the calculated value of ν H 1 S − 2 S ( B = 1.033 T) by using QED. Here the precision is limited by the short lifetime of the 2P state leading to a width of Γ 2 P ∼ 100 MHz.Įxperimental results of ¯ ¯¯ ¯ H are shown in Fig. ν 2 S − 2 P has recently been measured with improved precision of δ ν = 3 × 10 − 6 by the group of E. ν 1 S − 2 S and ν H F S are the most precisely measured transitions in hydrogen ( ν 1 S − 2 S with relative precision of δ ν = Δ ν / ν = 4.2 × 10 − 15, ν H F S with δ ν = 7 × 10 − 13 in a hydrogen maser ). 1 includes the measured quantities for the three most relevant transitions: the 1S–2S two-photon transition ν 1 S − 2 S, the Lamb shift ν 2 S − 2 P, and the ground-state hyperfine splitting ν H F S. In recent years, first results of laser spectroscopy of antihydrogen have been obtained by the ALPHA collaboration at the AD. Here we focus on measurements of masses and frequencies, since these quantities can easily be converted into each other. ![]() Studies of CPT comparing particle properties have been performed for a long time, an overview of measurements is published by the Particle Data Group PDG and a selection is shown in Fig. Precision stands for, unless otherwise stated, relative precision. In parallel, ASACUSA is operating a cold hydrogen beam for hyperfine spectroscopy, where the ground-state hyperfine structure of hydrogen was measured with 2.7 ppb precision 1 1 1In the following, A first measurement showed, as expected from the three-body recombination mechanism used, a population of states of predominantly high principle quantum numbers. Since then efforts are ongoing to increase the ¯ ¯¯ ¯ H production rate and the ground state population. The first production of antihydrogen in ASACUSA was achieved in 2010, and the first beam of antihydrogen ( ¯ ¯¯ ¯ H) in a field-free region was observed in 2014. The ASACUSA collaboration proposed to measure the ground-state hyperfine splitting of antihydrogen at the first PSAS conference in 2000. Antihydrogen is produced at the Antiproton Decelerator (AD) of CERN since 2000, and its extension to lower energies ELENA, which has just started operation in fall of 2021. ![]() Future perspectives of precision measurements of trapped antihydrogen in the ALPHA apparatus when the ELENA facility becomes available to experiments at CERN are discussed.This article is part of the Theo Murphy meeting issue 'Antiproton physics in the ELENA era'.ĬPT invariance Lamb shift antihydrogen antiproton charge radius laser spectroscopy symmetry violations.Antihydrogen is one of the most sensitive tools to study CPT symmetry, since it is the simplest anti-atom and its CPT conjugate counterpart, hydrogen, is one of the most precisely studied atomic systems. Prospects of measuring the Lamb shift and determining the antiproton charge radius in trapped antihydrogen in the ALPHA apparatus are presented. Here, the most recent work of the ALPHA collaboration on precision spectroscopy of antihydrogen is presented together with an outlook on improving the precision of measurements involving lasers and microwave radiation. The hyperfine spectrum of antihydrogen is determined to a relative uncertainty of 4×10 -4 The excited state and the hyperfine spectroscopy techniques currently both show sensitivity at the few 100 kHz level on the absolute scale. The result is consistent with CPT invariance at a relative precision of around 2×10 -10 This constitutes the most precise measurement of a property of antihydrogen. Owing to the narrow intrinsic linewidth of the 1S-2S transition and use of two-photon laser excitation, the transition energy can be precisely determined in both hydrogen and antihydrogen, allowing a direct comparison as a test of fundamental symmetry. The former constitutes the first observation of resonant interaction of light with an anti-atom, and the latter is the first detailed measurement of a spectral feature in antihydrogen. Both the 1S-2S transition and the ground state hyperfine spectrum have been observed in trapped antihydrogen.
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