Effects of nuclear charge fluctuations on dilepton photoproduction

Fluctuations of dilepton production from two photon interactionsγγ→l^+l^-are studied in semicentral and peripheral nuclear collisions.Based on the Weizsacker-Williams approach,electromagnetic(EM)fields generated by moving nuclear charges are approximated as quasi-real photons.As fluctuating EM fields in each collision event are hard to be measured directly in experiments due to its short lifetime,we study the dilepton photoproduction with fluctuating EM fields,which are crucial for the EM fields induced chiral and charged particle evolutions,and calculate the relative standard deviation of the dilepton mass spectrum with the event-by-event fluctuating nuclear charge distributions.This fluctuation effect becomes smaller in more peripheral collisions where the shift of proton positions is implicit for EM fields outside the nucleus.The uncertainty of effective impact parameter△b on the standard deviation is also studied,and its effect is around one-third of the effect of nuclear charge fluctuations when△b is taken as^1 fm.