Experimental Study Of Direct Photon Emission In K- -> Pi(-)Pi(0)Gamma Decay Using Istra+ Detector

The branching ratio in the charged-pion-kinetic-energy region of 55 to 90 MeV for the direct photon emission in the K- --> pi(-)pi(0)gamma decay has been Measured using in-flight decays detected with the ISTRA+ setup operating in the 25-GeV/c negative secondary beam of the U-70 PS. The value Br(DE) = [0.37 +/- 0.39(stat.) +/- 0.10(syst.)] X 10(-5) obtained from the analysis of 930 completely reconstructed events is consistent with the average Value of two stopped-kaon experiments, but it differs by 2.5 standard deviations from the average Value of three in-flight-kaon experiments. The result is also compared with recent theoretical predictions.