Probing Meson Spectral Functions with Double Differential Dilepton Spectra in Heavy-Ion Collisions

The double differential dilepton spectrum dN/ (dM² dM _^ ²)
at fixed transverse mass M _^ allows a direct access to the vector meson spectral
functions. Within a fireball model the sensitivity of dN/ (dM²dM _^ ²) against variations of both the in-medium properties of mesons and the dynamics of the fireball is investigated. In contrast to the integrated invariant-mass spectrum dN/dM², in the spectrum dN/dM²dM _^ ² with fixed M _^ the ω signal is clearly seen as bump riding on the ρ background even in case of strong in-medium modifications.