Repolarization of Negative Muons by Polarized $^{209}$Bi Nuclei

TL;DR

This study demonstrates the polarization of negative muons in polarized $^{209}$Bi nuclei using hyperfine interactions, revealing a significant muon polarization aligned with nuclear polarization, and compares experimental results with theoretical predictions.

Contribution

The paper reports the first observation of muon polarization transfer in polarized $^{209}$Bi nuclei, highlighting the role of hyperfine interactions in muonic atoms.

Findings

Achieved a muon polarization of approximately -1.07 in polarized $^{209}$Bi nuclei.

Observed a decay asymmetry of about 13.1%, indicating significant muon polarization.

Experimental results are nearly consistent with theoretical calculations based on hyperfine interaction models.

Abstract

A large $\mu^-$ polarization was achieved in muonic Bi atoms with the help of the strong hyperfine field in a polarized nuclear target. Using $^{209}$Bi nuclei polarized to ($59\pm9$)% in ferromagnetic BiMn, we observed a $\mu$-$e$ decay asymmetry of ($13.1\pm3.9$)%, which gives $\mu^-$ polarization per nuclear polarization equal to $-1.07\pm 0.35$. This value is almost consistent with $-0.792$ calculated for nuclei with spin $I= \frac{9}{2}$ and a positive magnetic moment under the assumption that the hyperfine interaction becomes effective in the lowest muonic states.