Search for critical fluctuations of the proton density in central A+A collisions at maximum SPS energy

Abstract

We performed an intermittency analysis of the proton density fluctuations in transverse momentum space for the collisions Si+A (A=Al,Si,P) and C+A (A=C,N) at maximum SPS energy $\sqrt {s_{NN} }$ ≈ 17 GeV). In our analysis we used exclusively proton tracks in the midrapidity region (|y _CM | ≤ 0.75). For the Si+A system we find signature of power-law distributed density fluctuations quantified by the intermittency index ϕ ₂ which approaches in size the predictions of critical QCD [Phys. Rev. Lett. 97, 032002 (2006)]. This result supports further the recent findings of power-law fluctuations in the density of (π ⁺, π ⁻) pairs with invariant mass close to their production threshold for the Si+Si at the same energy, reported in [Phys. Rev. C 81, 064907 (2010)].