Energy and system size dependence of strongly intensive fluctuation measures in heavy-ion collisions at FAIR energies

Abstract

Event-by-event fluctuations of multiplicity and transverse momentum of charged hadrons produced in heavy-ion collisions at FAIR energies, 10A, 20A, 30A and 40A GeV are studied in the framework of relativistic transport model, URQMD. Dependence of two families of strongly intensive measures of multiplicity($N$) and transverse momentum($p_{\rm T}$) fluctuations, $\Delta[p_{\rm T},N]$ and $\Sigma[p_{\rm T},N]$, on collision centrality, centrality bin-widths and pseudorapidity windows are examined. Attempts are also made to study $NN$, $N$$p_{\rm T}$ and $p_{\rm T}$$p_{\rm T}$ fluctuations using two window analysis method. The findings suggest that the measure, $\Delta[p_{\rm T},N]$ be dealt with proper selection of centrality intervals. This measure also exhibits a strong dependence on the widths of $\eta$ windows. The variable $\Sigma[p_{\rm T},N]$, however, is observed to be insensitive to the centrality bin-widths and shows a variation of $< 5\%$ with the widths of $\eta$ windows. The analysis of data after event mixing gives $\Delta[p_{\rm T},N]$ and $\Sigma[p_{\rm T},N]$ values as $\sim 1$ irrespective of the widths of $\eta$ windows and collision centrality, as predicted by model of independent particle emission, IPM. The study of joint fluctuations of the two quantities on two $\eta$ windows separated in $\eta$ space, reveals that $\Sigma[N_{\rm F},N_{\rm B}]$ values are $\sim 1$ irrespective of the position of $\eta$ windows whereas, the values of $\Sigma[N_{\rm F},p_{\rm T_B}]$ and $\Sigma[p_{\rm T_F},p_{\rm T_B}]$ firstly increase with $\eta_{sep}$ and later acquire saturations. The observed trend of centrality dependence of $\Sigma[N_{\rm F},N_{\rm B}], \Sigma[N_{\rm F},p_{\rm T_B}]$ and $\Sigma[p_{\rm T_F},p_{\rm T_B}]$ agrees fairly well with those observed in MC simulated studies carried out for AA collisions at LHC energies in the framework model of string fusion.