First observation of two hyperfine transitions in antiprotonic He-3

TL;DR

This paper reports the first microwave spectroscopic measurements of hyperfine transitions in antiprotonic He-3, providing experimental data to test three-body QED calculations and determine the antiproton's magnetic moment.

Contribution

It presents the first experimental observation of specific hyperfine transitions in antiprotonic He-3, enabling comparison with theoretical predictions and advancing understanding of antiprotonic helium.

Findings

Observed two SSHF transition lines at 11.12559 GHz and 11.15839 GHz.

Measured transition frequencies are within 1 MHz of theoretical values.

Experimental results support theoretical calculations of hyperfine structure.

Abstract

We report on the first experimental results for microwave spectroscopy of the hyperfine structure of antiprotonic He-3. Due to the helium nuclear spin, antiprotonic He-3 has a more complex hyperfine structure than antiprotonic He-4 which has already been studied before. Thus a comparison between theoretical calculations and the experimental results will provide a more stringent test of the three-body quantum electrodynamics (QED) theory. Two out of four super-super-hyperfine (SSHF) transition lines of the (n,L)=(36,34) state were observed. The measured frequencies of the individual transitions are 11.12559(14) GHz and 11.15839(18) GHz, less than 1 MHz higher than the current theoretical values, but still within their estimated errors. Although the experimental uncertainty for the difference of these frequencies is still very large as compared to that of theory, its measured value agrees with theoretical calculations. This difference is crucial to be determined because it is proportional to the magnetic moment of the antiproton.