Microwave spectroscopic study of the hyperfine structure of antiprotonic helium-3

TL;DR

This study measures the hyperfine structure of antiprotonic helium-3 with improved precision, comparing experimental results to theoretical predictions and assessing collision rates with helium atoms.

Contribution

First precise measurements of specific hyperfine transition lines in antiprotonic helium-3, enhancing understanding of its structure and collision dynamics.

Findings

Measured transition frequencies with 25-43% increased precision.

Experimental values agree with theoretical predictions within errors.

Estimated elastic and inelastic collision rates with helium atoms.

Abstract

In this work we describe the latest results for the measurements of the hyperfine structure of antiprotonic helium-3. Two out of four measurable super-super-hyperfine SSHF transition lines of the (n,L)=(36,34) state of antiprotonic helium-3 were observed. The measured frequencies of the individual transitions are 11.12548(08) GHz and 11.15793(13) GHz, with an increased precision of about 43% and 25% respectively compared to our first measurements with antiprotonic helium-3 [S. Friedreich et al., Phys. Lett. B 700 (2011) 1--6]. They are less than 0.5 MHz higher with respect to the most recent theoretical values, still within their estimated errors. Although the experimental uncertainty for the difference of 0.03245(15) GHz between these frequencies is large as compared to that of theory, its measured value also agrees with theoretical calculations. The rates for collisions between antiprotonic helium and helium atoms have been assessed through comparison with simulations, resulting in an elastic collision rate of gamma_e = 3.41 +- 0.62 MHz and an inelastic collision rate of gamma_i = 0.51 +- 0.07 MHz.