A search for direct processes in two pion radiative decays of positive and negative kaons

Decays of the type K+/- -> pi+/- pi0 gamma, have been observed in an experiment performed at Argonne National Laboratory using a scintillation counteroptical spark chamber arrangement, and a 3.5 Bev/c K±- beam. These decays are interesting because the interference of two competing mechanisms for this decay may produce asymmetries in the partial decay rates for K+ and K- into this mode. The mechanisms are internal bremsstrahlung and a hypothetical direct process in which the gamma is produced within the decay vertex. The experiment was performed to compare the partial rates of + +00 - -00 K ~ 1{ 1{ 1{ and K ~ 1{ 1{ n: as a method of observing CP asymmetries. Among the 3n: decays we have found 33 events of the type K+ - pi+pi0pi0 and K- -> pi-pi0pi0 of the type K- .~ - 0 1{ 1{ ,. These events were separated from the 3n: decays by observing an angle of the charged pion relative to the K±- direction larger than that kinematically allowed for the 3n: decays. The angles of the decay product in K+/- -> pi+pio gamma were used to calculate the K rest system energies and angles of the decay products. The distribution of the cosine of the angle between the charged pion and the gamma in the center of mass was used to fit parameters corresponding to the fraction of direct decays in the sample. The fraction of direct decays is consistent with zero, and the partial decay rate for direct decay,excluding interference between direct and internal bremsstrahlung amplitudes, is less than l0% (to 1 standard deviation) of the partial rate for internal bremsstrahlung for the kinetic energy of the charged pion between 58 and 90 Mev. The resulting upper limit for the asymmetries in the partial decay rates for K- -> pi- pio gamma, and [equation] one standard deviatjion for the same energy region. So, although the size of the direct process is small relative to internal bremsstrahlung, CP asymmetries have not been shown to be unobservable.U of I OnlyThesi