THE 2-PHOTON 2S-]1S TRANSITION OF THE FULLY-IONIZED MUONIC BORON MIGRATING IN HELIUM

In recent experiments performed at the Paul Scherrer Institute (PSI) m easurements were made of the yield Y-2 gamma of the two-photon 2s --> 1s transition of the fully-ionized muonic boron formed and quenched in a gaseous mixture of diborane B2H6 and helium. In the present work th is yield is calculated for an idealized case of a very low diborane de nsity when the main 2s state decay modes competing with the two-photon transition are due to the electron transfer from helium to the mu-ion . As the rate of this transfer depends strongly on the relative veloci ty, a treatment is needed of the whole kinetics of processes occurring with the mu-ion in helium. Accordingly, within the optical model with a complex potential constructed before we calculate cross-sections of the elastic scattering and electron transfer. Then the time evolution of the mu-ion energy is considered and, finally, the yield Y-2 gamma is calculated. It proves that at helium pressures P-He greater than or equal to 50 Torr this yield may be written in the form: (Y-z gamma)(- 1) = C(1 + PHeD); where the factor C is greater than unity and increas es rapidly with the initial energy E-0 which the mu-ion has after its formation in the diborane molecule. Thus measurement of the pressure d ependence of Y-2 gamma allows E-0 to be estimated. The results obtaine d make it possible to suggest a similar parametrization of the PSI dat a.