Improved intermittency analysis of proton density fluctuations in NA49 ion collisions at 158 AGeV

Abstract

The existence of the QCD critical point is a controversial issue, which is expected to be clarified in current ion collision experiments. In the vicinity of the critical point, according to recent theoretical investigations, the chiral condensate (chiral order parameter) should exhibit critical fluctuations (self-similarity and scale-invariance). These fluctuations should also be present in the transverse momentum distributions of protons produced in ion collision experiments due to the coupling of the chiral condensate with the net-proton density. We use intermittency analysis to calculate the 2nd scaled factorial moment (SSFM) of transverse momenta of protons produced around mid-rapidity in central A+A collisions at the NA49 experiment (SPS,CERN). Three different systems are analysed (C+C, Si+Si and Pb+Pb). We develop techniques in order to improve the traditional intermittency approach, estimating the level of non-critical background and correcting for systematic methodological errors that arise in the case of low statistics. We find evidence of powerlaw dependence of the SSFM (intermittency) in the case of Si+Si and Pb+Pb systems. Furthermore, we perform a suitable correlation analysis in order to test and rule out the possibility that the observed behaviour is influenced by misidentified split tracks (spurious correlations) in the analysed data sets.