Transverse Momentum Distributions and String Percolation Study in p+p,   d+Au and Au+Au at $\sqrt{s_{NN}}$ = 200 GeV
  Multiparticle production at high energies is described in terms of color strings stretched between the projectile and target. As string density increases, overlap among the strings leads to cluster formation. At some critical density a macroscopic cluster appears, spanning the entire system. This marks the percolation phase transition. Data from p+p, d+Au and Au+Au collisions at 200 GeV has been analyzed using the STAR detector to obtain the percolation density parameter, $\eta$. For 200 GeV Au+Au collisions, the value of $\eta$ is found to lie above the critical percolation threshold, while for 200 GeV d+Au collisions it is below the critical value. This supports the idea of string percolation, which at high enough string density is a possible mechanism to explore the hadronic phase transition to a quark-gluon plasma. 
Terence J. Tarnowsky, Brijesh K. Srivastava, Rolf P. Scharenberg (for   the STAR Collaboration)