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Experimental study of $μ$--atomic and $μ$--molecular processes in pure helium and deuterium--helium mixtures

We present experimental results of $μ$--atomic and $μ$--molecular processes induced by negative muons in pure helium and helium--deuterium mixtures. The experiment was performed at the Paul Scherrer Institute (Switzerland). We measured muonic x--ray $K$ series transitions relative intensities in $(μ^{3,4}\mathrm{He})^*$ atoms in pure helium as well as in helium--deuterium mixture. The muon stopping powers ratio between helium and deuterium atoms and the $d μ^3 \mathrm{He}$ radiative decay probability of for two different helium densities in $\mathrm{D}_2 + {}^3\mathrm{He}$ mixture were also determined. Finally, the $\mathrm{q}_{1s}^{\mathrm{He}}$ probability for a $dμ$ atom formed in an excited state to reach the ground state was measured and compared with theoretical calculations using a simple cascade model.