Measurement of direct photon emission in the KL→π+π-γ decay mode

In this paper the KTeV collaboration reports the analysis of 112.1x103 candidate KL→π+π-γ decays including a background of 671±41 events with the objective of determining the photon production mechanisms intrinsic to the decay process. These decays have been analyzed to extract the relative contributions of the CP violating bremsstrahlung process and the CP conserving M1 and CP violating E1 direct photon emission processes. The M1 direct photon emission amplitude and its associated vector form factor parameterized as g-tildeM1(1+(a1/a2/(Mρ2-MK2)+2MKEγ)) have been measured to be g-tildeM1=1.198±0.035(stat)±0.086(syst) and a1/a2=-0.738±0.007(stat)±0.018(syst) GeV2/c2 respectively. An upper limit for the CP violating E1 direct emission amplitude gE1≤0.21 (90%CL) has been found. The overall ratio of direct photon emission (DE) to total photon emission including the bremsstrahlung process (IB) has been determined to be DE/(DE+IB)=0.689±0.021 for Eγ≥20 MeV