Proton-number fluctuations ins root S-NN=2.4 GeV Au + Au collisions studied with the High-Acceptance DiElectron Spectrometer (HADES)

We present an analysis of proton-number fluctuations in root S-NN = 2.4 GeV Au-197 + Au-197 collisions measured with the High-Acceptance DiElectron Spectrometer (HADES) at GSI Helmholtzzentrum fur Schwerionenforschung, Darmstadt. With the help of extensive detector simulations done with Isospin Quantum Molecular Dynamics (IQMD) transport model events including nuclear clusters, various nuisance effects influencing the observed proton cumulants have been investigated. Acceptance and efficiency corrections have been applied as a function of fine-grained rapidity and transverse momentum bins, as well as considering local track density dependencies. Next, the effects of volume changes within particular centrality selections have been considered and beyond-leading-order corrections have been applied to the data. The efficiency and volume-corrected proton number moments and cumulants K-n of orders n = 1, 2, 3, and 4 have been obtained as a function of centrality and phase-space bin, as well as the corresponding correlators C-n. We find that the observed correlators show a power-law scaling with the mean number of protons, i.e., C-n proportional to < N >(n), indicative of mostly long-range multiparticle correlations in momentum space. We also present a comparison of our results with Au + Au collision data obtained at the Relativistic Heavy Ion Collider (RHIC) at similar centralities but higher root S-NN.