Critical fluctuations of the proton density in A+A collisions at 158A GeV

Abstract

We look for fluctuations expected for the QCD critical point using an intermittency analysis in the transverse momentum phase space of protons produced around midrapidity in the 12.5 % most central C+C, Si+Si and Pb+Pb collisions at the maximum SPS energy of 158A GeV. We find evidence of power-law fluctuations for the Si+Si data. The fitted power-law exponent $$\phi _{2} = 0.96^{+0.38}_{-0.25}\text { (stat.)}$$ $$\pm $$ $$0.16\text { (syst.)}$$ is consistent with the value expected for critical fluctuations. Power-law fluctuations had previously also been observed in low-mass $$\pi ^+ \pi ^-$$ pairs in the same Si+Si collisions.