Optimization of muonium yield in perforated silica aerogel

A muonium consists of a positive muon associated with an orbital electron, and the spontaneous conversion to antimuonium serves as a clear indication of new physics beyond the Standard Model in particle physics. One of the most important aspects in muonium-to-antimuonium conversion experiment is to increase the muonium yield in vacuum to challenge the latest limit obtained in 1999. This study focuses on a simulation of the muonium formation and diffusion in the perforated silica aerogel. The independent simulation results can be well-validated by experimental data. By optimizing the target geometry, we find a maximum muonium emission efficiency of 7.92(2)% and a maximum vacuum yield of 1.134(2)% with a typical surface muon beam, indicating a 2.6 times and a 2.1 times enhancement, respectively. Our results will pave the way for muonium experiments.

Figure 1

The schematic diagram of muonium emission in the silica aerogel target.

Figure 2

The muonium formation and tracking algorithm in the simulation.

Figure 3

The spacetime distribution of muonium decay. The simulation histogram and an exponential muon decay background are fit to the experimental histogram.

Figure 4

A comparison of muonium emission efficiency in simulation and experiment.

Figure 5

Muonium production and emission from a flat silica aerogel target with different aluminium degraders ($t_{\text{target}}=10\mathrm{mm},{\rho }_{\text{target}}=30\mathrm{mg}/{\mathrm{cm}}^3,\lambda =200\mathrm{nm}$, and $T=322\mathrm{K}$).

Figure 6

Projection of total muonium yield, muonium emission efficiency, and vacuum muonium yield under different beam conditions and target geometries.