Interactions between hadrons are strongly modified near the QCD (tri)critical point

Abstract

The QCD (tri)critical point, a genuine second-order phase transition, implies existence of a massless scalar mode, and singular behavior near it. In this work we however focus on the finite region around it, defined by a condition $m_\sigma=2m_\pi$. We point out that in this region the inter-hadron interaction should be dramatically changed. Light sigma should increase attractive mean field potentials for baryons and non-Goldstone mesons. The same effect can be observed in additional downward shift of the mass of vector mesons $\rho,\omega,\phi$, accessible via dilepton experiments. For pions we predict that the mean change due to light sigma is in fact a $repulsive$ mean potential. The implications of these effects for collective pion and nucleon flows, radial directed and elliptic, are estimated. Finally, we speculate tha unusual behavior of flows observed by NA49 at 40 GeV PbPb collisions at SPS may be explained by location of the critical point region nearby.