Continuous particle emission: a probe of thermalized matter evolution?

Continuous particle emission during the whole expansion of thermalized matter is studied and a new formula for the observed transverse mass spectrum is derived. In some limit, the usual emission in the freeze-out scenario (Cooper-Frye formula) may be recovered. This scenario changes completely the usual interpretation of transverse momentum spectra, may help to understand data on strange particle ratios and is possible to include in hydrodynamical codes.