= Solution
Particles are lost when a process drives their transverse amplitude or energy outside the machine's accepted region. Principal causes include scattering from residual gas; <Touschek scattering> within a bunch, which can convert transverse momentum into excessive longitudinal momentum; collision losses at an interaction point; diffusion from nonlinear resonances, field or RF noise; and collective instabilities or insufficient RF acceptance. Mechanical aperture restrictions turn large-amplitude motion into a loss.
Synchrotron-radiation energy loss is normally replenished by RF, so it does not by itself remove one electron for each emitted photon. Rare large energy deviations can nevertheless contribute to losses if they exceed the accepted energy range. Continuous top-up injection can hide the underlying decay and must be accounted for when measuring a lifetime.
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