  It was shown that the particle distribution detected by a uniformly
accelerated observer in the inertial vacuum (Unruh effect) deviates from the
pure Planckian spectrum when considering the superposition of fields with
different masses. Here we elaborate on the statistical origin of this
phenomenon. In a suitable regime, we provide an effective description of the
emergent distribution in terms of the nonextensive q-generalized statistics
based on Tsallis entropy. This picture allows us to establish a nontrivial
relation between the q-entropic index and the characteristic mixing parameters
sin{\theta} and \Delta m. In particular, we infer that q < 1, indicating the
superadditive feature of Tsallis entropy in this framework. We discuss our
result in connection with the entangled condensate structure acquired by the
quantum vacuum for mixed fields.
