Saehanseul Oh (Yale University)

Particle correlations in the longitudinal direction in relativistic heavy ion collisions

Longitudinal multiplicity correlations and longitudinal asymmetry studies have suggested a hint of some asymmetry in the initial geometry and its effects in the final state particle fluctuations in relativistic heavy ion collisions. In addition to the expansion of the medium in the transverse direction, commonly quantified using Fourier coefficients (v_n), the initial geometry and resulting longitudinal expansion as a function of azimuthal angle enable us to better understand the full 3-dimensional picture of heavy-ion collisions. In this talk, we will summarize recent analyses on particle correlations in the longitudinal direction, and show the latest ALICE results on azimuthal dependence of the longitudinal structure with comparisons to models. Analogous to the correlation analyses in the transverse direction, we will explore mathematical decompositions of the event by event pseudo-rapidity distributions, and discuss physical meaning of the extracted coefficients. Finally, we will explore how these coefficients relate to the reaction plane direction.