title: Observation of double radiative capture on pionic hydrogen.
abstract: We report the first observation of double radiative capture on pionic hydrogen. The experiment was conducted at the TRIUMF cyclotron using the RMC spectrometer and detected gamma-ray coincidences following pi(-) stops in liquid hydrogen. We found the branching ratio for double radiative capture to be [3.05+/-0.27(stat)+/-0.31(syst)]x10(-5). The measured branching ratio and angle-energy distributions support the theoretical prediction of a dominant contribution from the pipi-->gammagamma annihilation mechanism.
authors.affiliation: University of Kentucky, Lexington 40506, USA.
authors.forename: S
authors.initials: S
authors.lastname: Tripathi
authors.forename: D S
authors.initials: DS
authors.lastname: Armstrong
authors.forename: M E
authors.initials: ME
authors.lastname: Christy
authors.forename: J H D
authors.initials: JH
authors.lastname: Clark
authors.forename: T P
authors.initials: TP
authors.lastname: Gorringe
authors.forename: M D
authors.initials: MD
authors.lastname: Hasinoff
authors.forename: M A
authors.initials: MA
authors.lastname: Kovash
authors.forename: D H
authors.initials: DH
authors.lastname: Wright
authors.forename: P A
authors.initials: PA
authors.lastname: Zołnierczuk