Determination of K X-Ray Yields in Pionic Hydrogen as a Function of Gas Pressure

The S-wave scattering lengths a 1 and a 3 are among the most interesting quantities in pion-nucleon physics. An experiment is planned1 at PSI to determine these scattering lengths from a determination of the strong shift (e 0 ) and width (Γ) of the Is level in pionic hydrogen with a crystal spectrometer. As a first step we have measured in the present work the absolute X-ray yields in pionic hydrogen as a function of gas pressure with the aim of obtaining an improved understanding of the atomic cascade processes (Stark mixing, Auger effect, Coulomb deexcitation etc...).