However, a discrepancy remains between laser spectroscopic measurements and measurements with other methods. A recent laser spectroscopic measurement of the Rydberg constant and proton size from atomic hydrogen is consistent with results from muonic hydrogen. This discrepancy is known as the ‘proton radius puzzle’. However, in 2010 a measurement of the Lamb shift in muonic hydrogen (a bound state of a proton and a muon) yielded a proton charge radius 5 σ smaller compared to the CODATA value. It is because such high accuracy can be achieved in hydrogen, and because on the whole the hydrogen atom is a well-understood system, that a comparison with antihydrogen is so compelling. The ground state hyperfine interval is determined from experiments on the hydrogen maser with an uncertainty down to 1 mHz corresponding to a relative uncertainty of 0.7×10 −12. Today, the 1S–2S transition in hydrogen is known with an uncertainty of only 10 Hz, which corresponds to a relative uncertainty of 4×10 −15. For example, the discovery that the 2S and 2P states in hydrogen do not have the same energy (now known as the Lamb shift) is inextricably linked with the development of quantum electrodynamics (QED). Measurements of the hydrogen spectrum together with its interpretation have a long and illustrious history which is intimately linked with the development of quantum mechanics. Thus, the collaboration has shown not just that the basic tools for precision spectroscopy of antihydrogen are available, but also provided a first, ground-breaking test of CPT invariance with anithydrogen. Very recently, the collaboration has observed the 1S–2S transition, and the ground state hyperfine spectrum. New techniques to study antihydrogen have emerged the ALPHA collaboration at CERN can now interrogate the ground state energy structure with resonant microwaves, determine the gravitational mass to inertial mass ratio and measure charge neutrality. Antihydrogen can reproducibly be synthesized and trapped in the laboratory for extended periods of time, offering an opportunity to study the properties of antimatter in detail. In particular, the CPT (charge, parity and time) theorem requires that hydrogen and antihydrogen have the same spectrum. This article is part of the Theo Murphy meeting issue ‘Antiproton physics in the ELENA era’.Īntihydrogen, the antimatter equivalent of hydrogen, offers a unique way to test matter–antimatter symmetry. Future perspectives of precision measurements of trapped antihydrogen in the ALPHA apparatus when the ELENA facility becomes available to experiments at CERN are discussed. 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 excited state and the hyperfine spectroscopy techniques currently both show sensitivity at the few 100 kHz level on the absolute scale. The hyperfine spectrum of antihydrogen is determined to a relative uncertainty of 4×10 −4. This constitutes the most precise measurement of a property of antihydrogen. The result is consistent with CPT invariance at a relative precision of around 2×10 −10. 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. L2 - rfr_id=ori:rid:crossref.Both the 1S–2S transition and the ground state hyperfine spectrum have been observed in trapped antihydrogen. At energies up to a few tens of eV, I focus on simple approximations that give reasonably accurate results, as these allow quick estimates of collision rates without embarking on a research project.This article is part of the Theo Murphy meeting issue 'Antiproton physics in the ELENA era'. Instead I compare the results from different theoretical calculations, of various degrees of sophistication. At low energies (1 keV) there are practically no experimental data available. N2 - I give an overview of experimental and theoretical results for antiproton and antihydrogen scattering with atoms and molecules (in particular H, He).
#Cpt symmetry antihydrogen 2017 alpha pdf series#
Series A, Mathematical, physical, and engineering sciences T1 - Collisions involving antiprotons and antihydrogen: an overview.
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