Abstract
Kinetic energy distributions of muonic hydrogen atoms μp(IS) have been obtained by means of a time-of-flight technique for hydrogen gas pressures between 4 and 64 hPa. A high energy component of ∼900 eV observed in the data is interpreted as the signature of long-lived μp(2S) atoms, which are quenched in a non-radiative process leading to the observed high energy: the collision of a thermalized μp(2S) atom with a hydrogen molecule H 2 results in the resonant formation of a {[(ppμ) + ]*pee}* molecule. Then the (ppμ) + complex undergoes Coulomb de-excitation and the ∼1.9 keV excitation energy is shared between a μp(IS) atom and one proton. The preliminary analysis of the time spectra gives a long-lived μp(2S) population of ∼1% of all stopped muons, and a quenching rate of ∼4 · 10 11 s -1 .