title: Observation of long-lived muonic hydrogen in the 2S state.
abstract: The kinetic energy distribution of ground state muonic hydrogen atoms mup(1S) is determined from time-of-flight spectra measured at 4, 16, and 64 hPa H2 room-temperature gas. A 0.9 keV component is discovered and attributed to radiationless deexcitation of long-lived mu p(2S) atoms in collisions with H2 molecules. The analysis reveals a relative population of about 1%, and a pressure-dependent lifetime (e.g., 30.4 +21.4/-9.7 ns at 64 hPa) of the long-lived mu p(2S) population, equivalent to a 2S quench rate in mu p(2S)+H2 collisions of 4.4 +2.1/-1.8 x 10(11) s(-1) at liquid-hydrogen density.
authors.affiliation: Institut für Teilchenphysik, ETH Zürich, 8093 Zürich, Switzerland. Randolf.Pohl@mpq.mpg.de
authors.forename: Randolf
authors.initials: R
authors.lastname: Pohl
authors.forename: Herbert
authors.initials: H
authors.lastname: Daniel
authors.forename: F Joachim
authors.initials: FJ
authors.lastname: Hartmann
authors.forename: Peter
authors.initials: P
authors.lastname: Hauser
authors.forename: Franz
authors.initials: F
authors.lastname: Kottmann
authors.forename: Valery E
authors.initials: VE
authors.lastname: Markushin
authors.forename: Markus
authors.initials: M
authors.lastname: Mühlbauer
authors.forename: Claude
authors.initials: C
authors.lastname: Petitjean
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Schott
authors.forename: David
authors.initials: D
authors.lastname: Taqqu
authors.forename: Peter
authors.initials: P
authors.lastname: Wojciechowski-Grosshauser