MTscaling in dilepton spectrum as a signature for quark-gluon plasma

In general, the spectrum of lepton pairs produced in nuclear reactions depends on both invariant mass and momentum. But under a few reasonable assumptions on the time evolution of the system, we show that once the quark-gluon plasma is created in ultrarelativistic heavy ion collisions, the observed dilepton spectrum between the φ and J/ψ peak becomes dependent essentially only on its transverse mass ${\mathit{M}}_{\mathit{T}}$ and thus shows ${\mathit{M}}_{\mathit{T}}$ scaling. This scaling will not be observed if the quark-gluon plasma is not created in collisions.