Characterization of the 1S–2S transition in antihydrogen

Abstract

In 1928, Dirac published an equation that combined quantum mechanics and special relativity. Negative-energy solutions to this equation, rather than being unphysical as initially thought, represented a class of hitherto unobserved and unimagined particles-antimatter. The existence of particles of antimatter was confirmed with the discovery of the positron (or anti-electron) by Anderson in 1932, but it is still unknown why matter, rather than antimatter, survived after the Big Bang. As a result, experimental studies of antimatter, including tests of fundamental symmetries such as charge-parity and charge-parity-time, and searches for evidence of primordial antimatter, such as antihelium nuclei, have high priority in contemporary physics research. The fundamental role of the hydrogen atom in the evolution of the Universe and in the historical development of our understanding of quantum physics makes its antimatter counterpart-the antihydrogen atom-of particular interest. Current standard-model physics requires that hydrogen and antihydrogen have the same energy levels and spectral lines. The laser-driven 1S-2S transition was recently observed in antihydrogen. Here we characterize one of the hyperfine components of this transition using magnetically trapped atoms of antihydrogen and compare it to model calculations for hydrogen in our apparatus. We find that the shape of the spectral line agrees very well with that expected for hydrogen and that the resonance frequency agrees with that in hydrogen to about 5 kilohertz out of 2.5 × 10 hertz. This is consistent with charge-parity-time invariance at a relative precision of 2 × 10-two orders of magnitude more precise than the previous determination -corresponding to an absolute energy sensitivity of 2 × 10 GeV.

Status and Prospects for CPT Tests with the ALPHA Experiment

“…In 2018, ALPHA published a measurement of the 1S-2S transition inH in a 1 T field to a precision of 5 × 10 3 Hz out of 2.5 × 10 15 Hz. 10 This is consistent with CPT invariance at a relative precision of 2 × 10 −12 (corresponding to an energy sensitivity of 2 × 10 −20 GeV). This result has been used to put a constraint on CPT-violating SME coefficients, the first such constraint fromH spectroscopy.…”

“…Because the topology of the signal (annihilations) and background (cosmic rays) events are very different, they can be distinguished effectively by using machine-learning procedures. 6…”

Small Magnetic Charges and Monopoles in Nonassociative Quantum Mechanics

“…Moreover, the magnetic charge of the muon is more difficult to bound [28]. Our bound, on the other hand, also applies to a muon as the nucleus of muonium, and to antimatter such as the antiproton in antihydrogen [29,30] or the positron in positronium [31].…”

“…in a single independent variable, ℓ, with initial conditions a E 0 = 1 and a E 1 = E/ ω which follow from normalization and our leading-order results presented in the letter, respectively. Equations (30) and (31) determine all orders of moments in terms of E/ ω. It follows that a E ℓ is a polynomial in E/ ω of degree ℓ, with only even terms for ℓ even and only odd terms for ℓ odd.…”

Formation of antihydrogen beams from positron–antiproton interactions

“…Over the past few years the first quantitative tests of matter-antimatter symmetry using antihydrogen (H ) have been achieved by the ALPHA collaboration, including measurements based upon 1s-2s spectroscopy [1], via observation of the Lyman-α transition [2] and involving hyperfine transitions [3]. These, and other, advances were made possible by the confinement of H in magnetic minimum traps [4][5][6].…”