Non-thermal p/pi ratio at LHC as a consequence of hadronic final state   interactions
  Recent LHC data on Pb+Pb reactions at sqrt(s_{NN})=2.7 TeV suggests that the p/pi is incompatible with thermal models. We explore several hadron ratios (K/pi, p/pi, Lambda/pi, Xi/pi) within a hydrodynamic model with hadronic after burner, namely UrQMD 3.3, and show that the deviations can be understood as a final state effect. We propose the p/pi as an observable sensitive on whether final state interactions take place or not. The measured values of the hadron ratios do then allow to gauge the transition energy density from hydrodynamics to the Boltzmann description. We find that the data can be explained with transition energy densities of 840 +- 150 MeV/fm^3. 
Jan Steinheimer, J\"org Aichelin and Marcus Bleicher
nucl-th hep-ph