Muonic atom spectroscopy with microgram target material

TL;DR

This paper introduces a novel muonic atom spectroscopy technique using microgram-scale targets, enabling precise nuclear measurements with significantly less material than traditional methods.

Contribution

The authors developed a new transfer reaction method in a hydrogen gas cell that reduces target material requirements for muonic atom spectroscopy.

Findings

Successful measurement of muonic x rays from a 5-microgram gold target.

Simulations align well with experimental data, confirming process understanding.

Method enables high-precision nuclear measurements with minimal target material.

Abstract

Muonic atom spectroscopy -- the measurement of the x rays emitted during the formation process of a muonic atom -- has a long standing history in probing the shape and size of nuclei. In fact, almost all stable elements have been subject to muonic atom spectroscopy measurements and the absolute charge radii extracted from these measurements typically offer the highest accuracy available. However, so far only targets of at least a few hundred milligram could be used as it required to stop a muon beam directly in the target to form the muonic atom. We have developed a new method relying on repeated transfer reactions taking place inside a 100-bar hydrogen gas cell with an admixture of 0.25% deuterium that allows us to drastically reduce the amount of target material needed while still offering an adequate efficiency. Detailed simulations of the transfer reactions match the measured data, suggesting good understanding of the processes taking place inside the gas mixture. As a proof of principle we demonstrate the method with a measurement of the 2p-1s muonic x rays from a 5-{\mu}g gold target.