Event-by-event fluctuation of rapidity distributions in heavy-ion collisions

Event-by-event fluctuation in rapidity distributions is investigated using the power spectrum method. Non-statistical fluctuation is artificially injected in a small subset of events. A reference power spectrum, obtained by using mixed events, is found to be almost independent of the level of admixture of non-statistical fluctuation. This makes the power spectrum directly applicable to experimental data. Simulation results are presented for the efficiency of identification of non-statistical fluctuations in the form of spikes and holes in the rapidity distributions of photons at SPS and LHC energies. The results for limited detector coverage are slightly poorer than those for large coverage. Reducing the bin size in rapidity improves the efficiency of identification for weaker signals.