Atomic capture and transfer of negative pions stopped in binary mixtures of hydrogen with polyatomic gases

Abstract The atomic capture and transfer of stopped negative pions have been studied in binary gas mixtures of H 2 + M , where M is CCl 2 F 2 , CClF 3 , CBrF 3 or SF 6 . The π 0 yield, versus relative atomic concentration C A of M , goes through a maximum at C A ∼ 0.1 and levels off at zero at high concentrations. This phenomenon together with other observed characteristics of the atomic capture and transfer of pions in these systems is interpreted in the frame of a phenomenological model. The average transfer coefficients \ gL Z exhibit a weak concentration dependence. The estimated average atomic capture ratios A ( Z H ) are lower than those found for noble gases, probably because of the mutual screening of the constituent atoms in the molecules. The probability of pion capture in an atomic orbit is not proportional to the stopping power of the components of the mixture.