Nuclear Theory/RIKEN Seminar

It has long been known that sub-nucleonic fluctuations of the energy density in the initial stages of heavy ion collisions play an important role in generating the observed distributions of particles and their flow. These energy density fluctuations are dominated by the radiation of small-x gluons which are populated to classically large occupation numbers in the wave functions of ultra-relativistic heavy ions. While these soft gluons dominate the initial conditions for the energy density, it is quark production which determines the initial conditions of other conserved charges, like flavor and baryon number. With the recent development of state-of-the art hydrodynamics codes tailored to the Beam Energy Scan which can propagate these conserved charges into the final state, it is timely and important to calculate the initial conditions of these conserved charges from first principles in QCD. In this talk, I will present new results for the spatial correlations among quarks and antiquarks produced at mid-rapidity by pair production from small-x gluons. This single-pair production mechanism, which has been studied for some time in momentum space, is the leading contribution to these correlations in coordinate space for dilute-dense collisions. As one moves from the dilute-dense regime toward the dense-dense regime, correlations due to double pair production become more important, and these correlations persist over larger length scales than the single-pair production mechanism. Over nonperturbative length scales, only the correlations from the overlap geometry remain. I will present explicit results for quark-antiquark correlations due to single pair production, and I will outline some preliminary results for the various double-pair production mechanisms. The ultimate goal of this work will be to construct a code which can initialize these conserved charges over all length scales in heavy-ion collisions.