RESUMO
Searches for the lepton number violating K^{+}âπ^{-}µ^{+}e^{+} decay and the lepton flavor violating K^{+}âπ^{+}µ^{-}e^{+} and π^{0}âµ^{-}e^{+} decays are reported using data collected by the NA62 experiment at CERN in 2017-2018. No evidence for these decays is found and upper limits of the branching ratios are obtained at 90% confidence level: B(K^{+}âπ^{-}µ^{+}e^{+})<4.2×10^{-11}, B(K^{+}âπ^{+}µ^{-}e^{+})<6.6×10^{-11} and B(π^{0}âµ^{-}e^{+})<3.2×10^{-10}. These results improve by 1 order of magnitude over previous results for these decay modes.
RESUMO
Experimental results for the radiative energy loss of 149, 207, and 287 GeV electrons in a thin Ir target are presented. From the data we conclude that at high energies the radiation length increases in accordance with the Landau-Pomeranchuk-Migdal (LPM) theory and thus electrons become more penetrating the higher the energy. The increase of the radiation length as a result of the LPM effect has a significant impact on the behavior of high-energy electromagnetic showers.