Influence of oxygen admixtures on the lifetime of metastable antiprotonic helium atoms

Two experiments have been performed at the CERN Low Energy Antiproton Ring (LEAR) facility to study the lifetime shortening of metastable antiprotonic helium atoms by the presence of ppm admixtures of oxygen. The change in shape and lifetime of the delayed annihilation time spectra can be reproduced fairly well by fitting a simple four-level model to the data and assuming equal quenching cross sections for all metastable levels. From this we deduce a quenching cross section of [Formula Presented] at a temperature of 100 K. An analysis of data from a previous experiment gives a value for the quenching cross section at room temperature of [Formula Presented] Resonant laser deexcitation of the levels [Formula Presented] and [Formula Presented] (the lowest metastable levels of the cascades [Formula Presented] and [Formula Presented] respectively) was used to examine the time development of the population of these levels. Quenching cross sections of [Formula Presented] and [Formula Presented] were deduced for the [Formula Presented] and [Formula Presented] cascades from these studies at 100 K.