  We study production and equilibration of pions and muons in relativistic
electron-positron-photon plasma at a temperature $T\ll m_\mu, m_\pi $. We argue
that the observation of pions and muons can be a diagnostic tool in the study
of the initial properties of such a plasma formed by means of strong laser
fields. Conversely, properties of muons and pions in thermal environment become
accessible to precise experimental study.

High Energy Physics - Phenomenology;Nuclear Experiment;Nuclear Theory;Optics;Plasma Physics