Systematic effects in the measurement of the negatively charged pion mass using laser spectroscopy of pionic helium atoms

TL;DR

This paper calculates collision-induced shifts and broadenings of pionic helium spectral lines at low temperatures to improve the accuracy of pion mass measurements via laser spectroscopy.

Contribution

It provides theoretical predictions of frequency shifts and broadening effects in pionic helium, aiding future experimental precision in pion mass determination.

Findings

Blue shift predicted for certain unfavored transitions

Red shift predicted for favored transition

Results can help reduce systematic errors in pion mass measurements

Abstract

The collision-induced shift and broadening of selected dipole transition lines of pionic helium in gaseous helium at low temperatures up to $T=12$ K and pressure up to a few bar are calculated within variable phase function approach. We predict blue shift of the resonance frequencies of the $(n,l)=(16,15) \rightarrow (16,14) $ and $(16,15) \rightarrow (17,14)$ unfavored transitions and red shift for the favored transition $(17,16) \rightarrow (16,15)$. The result may be helpful in reducing the systematic error in proposed future experiments for determination of the negatively charged pion mass from laser spectroscopy of metastable pionic helium atoms.