In this paper a new procedure to smooth out the initial energy densities of hydrodynamics is employed to show that the initial spatial eccentricities m,n, which drive the final state flow harmonics vn, are remarkably robust with respect to variations of the underlying scale of initial energy density spatial gradients, λ, in nucleus-nucleus collisions. For s=2.76 TeV Pb+Pb collisions, the ϵm,n's (across centrality classes) change by less than 10% if the scale of fluctuations is varied from 0.1 to 1 fm. We show, using the 2+1 Lagrangian hydrodynamic code v-USPhydro, that this robustness is transferred to the final vn's computed within event-by-event viscous hydrodynamics. This indicates that the flow harmonics in nucleus-nucleus collisions are not particularly sensitive to the underlying microscopic subnucleon physics below the confinement scale. On the other hand, the eccentricities of top 1% high multiplicity s=5.02 TeV p+Pb collisions are found to be very sensitive to subnucleonic scale fluctuations, which should be contrasted with the robustness found in peripheral Pb+Pb collisions with the same multiplicity.
ASJC Scopus subject areas
- Nuclear and High Energy Physics