In-beam measurement of the hydrogen hyperfine splitting - towards antihydrogen spectroscopy

TL;DR

This paper reports a highly precise measurement of hydrogen's ground-state hyperfine splitting using a beam spectroscopy method, validating techniques for future antihydrogen CPT symmetry tests.

Contribution

It presents the first zero-field hydrogen hyperfine splitting measurement with beam spectroscopy, achieving ppb-level precision to support antihydrogen CPT symmetry experiments.

Findings

Measured hydrogen GS-HFS with 2.7×10^{-9} relative precision.

Validated spectroscopy methods for antihydrogen hyperfine measurements.

Established prerequisites for antihydrogen CPT symmetry tests.

Abstract

Antihydrogen, the lightest atom consisting purely of antimatter, is an ideal laboratory to study the CPT symmetry by comparison to hydrogen. With respect to absolute precision, transitions within the ground-state hyperfine structure (GS-HFS) are most appealing by virtue of their small energy separation. ASACUSA proposed employing a beam of cold antihydrogen atoms in a Rabi-type experiment to determine the GS-HFS in a field-free region. Here we present a measurement of the zero-field hydrogen GS-HFS using the spectroscopy apparatus of ASACUSA's antihydrogen experiment. The measured value of $\nu_\mathrm{HF}$=$1~420~405~748.4(3.4)(1.6)~\textrm{Hz}$ with a relative precision of $\Delta$$\nu_\mathrm{HF}$/$\nu_\mathrm{HF}$=$2.7\times10^{-9}$ constitutes the most precise determination of this quantity in a beam and verifies the developed spectroscopy methods for the antihydrogen HFS experiment to the ppb level. Together with the recently presented observation of antihydrogen atoms $2.7~\textrm{m}$ downstream of the production region, the prerequisites for a measurement with antihydrogen are now available within the ASACUSA collaboration.