Measurement of the charged pion mass using a low-density target of light atoms

TL;DR

This paper reports a precise measurement of the charged pion mass using simultaneous spectroscopy of pionic nitrogen and muonic oxygen in a low-density gas target, emphasizing the reduction of spectral line contamination.

Contribution

It introduces a novel experimental approach combining pionic and muonic spectroscopy with dilute gas targets to improve pion mass measurement accuracy.

Findings

Achieved a more precise pion mass value.

Demonstrated the effectiveness of dilute targets in spectral purity.

Applied Bayesian hypothesis testing to identify satellite lines.

Abstract

We present a new evaluation of the negatively charged pion mass based on the simultaneous spec-troscopy of pionic nitrogen and muonic oxygen transitions using a gaseous target composed by a N 2 /O 2 mixture at 1.4 bar. We present the experimental setup and the methods for deriving the pion mass value from the spatial separation from the 5g -- 4 f $\pi$N transition line and the 5g -- 4 f $\mu$O transition line used as reference. Moreover, we discuss the importance to use dilute targets in order to minimize the influence of additional spectral lines from the presence of remaining electrons during the radiative emission. The occurrence of possible satellite lines is investigated via hypothesis testing methods using the Bayes factor.