Effect of multiple scattering on the emission of ultrarelativistic electrons in a thin layer of matter

We develop a quantitative theory of the effect of multiple scattering on the bremsstrahlung of ultrarelativistic electrons in a thin layer of matter. The effect is an analog of the Landau-Pomeranchuk-Migdal (LPM) effect of suppression of the radiation emitted by high-energy particles in an infinite amorphous medium, but certain differences do exist. On the basis of our approach we analyze the data recently obtained at SLAC (E-146) in experiments set up to verify the LPM effect. We show that in addition to the LPM effect, this experiment exhibited the suppression of bremsstrahlung in a thin layer of matter, theoretically predicted in our earlier papers.