Room-temperature emission of muonium from aerogel and zeolite targets

TL;DR

This study demonstrates the first observation of muonium emission from zeolite targets into vacuum and measures the efficiency of muonium production from aerogel, advancing atomic beam development for fundamental physics experiments.

Contribution

It introduces new detection schemes for muonium, compares emission from different targets, and reports the first vacuum emission from zeolite, with efficiency measurements for aerogel targets.

Findings

Muonium emitted from zeolite targets into vacuum for the first time.

Achieved a muon-to-vacuum-muonium conversion efficiency of 7.23%.

Determined an upper temperature limit of 0.3 K for superfluid helium converters.

Abstract

A low-emittance, high-intensity atomic beam of muonium ($\mathrm{M}=\mu^+ + \mathrm{e}^-$) using superfluid helium as muon-to-muonium converter is being developed at the Paul Scherrer Institute (PSI). This beam could advance laser spectroscopy of muonium and allow the first atomic interferometry experiments for the direct observation of the M gravitational interaction. In this paper, we describe the development of compact detection schemes which resulted in the background-suppressed observation of atomic muonium in vacuum, and can be adapted for cryogenic measurements. Using these setups, we compared the emission characteristics of various muonium production targets using low momentum ($p_{\mu} = 11$-$13~$MeV/c) muons, and observed muonium emission from zeolite targets into vacuum for the first time. For a specific laser-ablated aerogel target, we determined a muon-to-vacuum-muonium conversion efficiency of $7.23 \pm 0.05 \text{(stat)} ^{+1.06}_{-0.76}\text{(sys)}\,\text{%}$, assuming thermal emission of muonium. Moreover, we investigated muonium-helium collisions and from it we determined an upper temperature limit of 0.3 K for the superfluid helium converter.