How Far Can We See Back in Time in High-Energy Collisions Using Charm Hadrons?

We use open charm production to estimate how far we can see back in time in high-energy hadron-hadron collisions. We analyze the transverse momentum distributions of the identified D mesons from pp, p-Pb and A-A collisions at the ALICE and STAR experiments covering the energy range from sNN=200GeV up to 7 TeV. Within a non-extensive statistical framework, the common Tsallis parameters for D mesons represent higher temperature and more degrees of freedom than that of light-flavour hadrons. Assuming Bjorken-expansion, the production of D mesons corresponds to a significantly earlier proper time, tau D = (0.18 +/- 0.06)tau LF.