Muonic hydrogen cascade time and lifetime of the short-lived $2S$ state

Abstract

Metastable $2S$ muonic-hydrogen atoms undergo collisional $2S$-quenching, with rates which depend strongly on whether the $\hat{I}¼p$ kinetic energy is above or below the $2S\to 2P$ energy threshold. Above threshold, collisional $2S\to 2P$ excitation followed by fast radiative $2P\to 1S$ deexcitation is allowed. The corresponding short-lived $\hat{I}¼p(2S)$ component was measured at 0.6 hPa ${\mathrm{H}}_2$ room temperature gas pressure, with lifetime $\ddot{I}{„}_{2S}^{\mathrm{short}}=165_{-29}^{+38}$ ns (i.e., $\hat{I}{»}_{2S}^{\mathrm{quench}}=7.9_{-1.6}^{+1.8}\times 10^{12}{\mathrm{s}}^{-1}$ at liquid-hydrogen density) and population $\hat{I}{\mu }_{2S}^{\mathrm{short}}=1.70_{-0.56}^{+0.80}$ % (per $\hat{I}¼p$ atom). In addition, a value of the $\hat{I}¼p$ cascade time, $T_{\mathrm{cas}}^{\hat{I}¼p}=(37\pm 5)$ ns, was found.

4 pages, 3 figures