Study of γ-charge correlation in heavy ion collisions, various approaches

Event-by-event \gamma-charge correlation is used in studying systems going through QCD chiral phase transition. In this paper various methods for measuring \gamma-charge correlation in heavy ion collisions have been discussed. Dynamical fluctuation due to formation of domains of DCC that can affect \gamma-charge correlation has been discussed. We study known detector and statistical effects involved in these measurements and suggest suitable robust observables \Delta\nu_{dyn} and r_{m,1} sensitive to small \gamma-charge correlation signal. These variables are constructed based on moments of multiplicity distributions of photon and charged particles. Estimations of expected measurable signals of \gamma-charge correlation from various available models such as for ideal Boltzmann gas of pions, monte-carlo models based on transport and mini-jets have been discussed. Collision centrality dependence of the observables have been estimated from Central Limit Theorem and found to be consistent with the model predictions. We find that observables show high sensitivity to fraction of DCC events and have nonlinear dependence on fraction of pions carrying DCC signals. Variation of r_{m,1} with orders of its higher moments m is an observable to extract the nature and strength of \gamma-charge correlation.