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Event-by-event charged-neutral fluctuations in Pb+Pb collisions at 158 A~GeV

Charged particles and photons have been measured in central Pb+Pb collisions at 158 A GeV in a common ($η$ - $ϕ$)-phase space region in the WA98 experiment at the CERN SPS. The measured distributions have been analyzed %using the sliding window method in order to quantify the frequency with which phase space regions of varying sizes have either small or large neutral pion fraction. The measured results are compared with VENUS model simulated events and with mixed events. Events with both large and small charged-neutral fluctuations are observed to occur more frequently than expected statistically, as deduced from mixed events, or as predicted by model simulations, with the difference becoming more prominent with decreasing size of the $Δη$ - $Δϕ$ region.