Measurement of the charged pion mass using X-ray spectroscopy of exotic atoms

TL;DR

This study precisely measured the charged pion mass using X-ray spectroscopy of exotic atoms, calibrating with muonic oxygen lines, and found a value slightly higher than the current world average.

Contribution

It introduces a novel high-precision measurement technique for the charged pion mass using simultaneous X-ray spectroscopy of pionic and muonic atoms.

Findings

Charged pion mass measured as 139.57077 MeV/c^2 with 1.3ppm precision.

The measured pion mass is 4.2ppm larger than the current world average.

Method provides a new benchmark for fundamental particle mass measurements.

Abstract

The $5g-4f$ transitions in pionic nitrogen and muonic oxygen were measured simultaneously by using a gaseous nitrogen-oxygen mixture at 1.4\,bar. Due to the precise knowledge of the muon mass the muonic line provides the energy calibration for the pionic transition. A value of (139.57077\,$\pm$\,0.00018)\,MeV/c$^{2}$ ($\pm$\,1.3ppm) is derived for the mass of the negatively charged pion, which is 4.2ppm larger than the present world average.