Cumulants and nonlinear response of high pT harmonic flow at s NN =5.02 TeV

Event-by-event fluctuations caused by quantum mechanical fluctuations in the wave function of colliding nuclei in ultrarelativistic heavy ion collisions were recently shown to be necessary for the simultaneous description of RAA as well as the elliptic and triangular flow harmonics at high pT in PbPb collisions at the Large Hadron Collider (LHC). In fact, the presence of a finite triangular flow as well as cumulants of the flow harmonic distribution that differ from the mean are only possible when these event-by-event fluctuations are considered. In this paper we combine event-by-event viscous hydrodynamics and jet quenching to make predictions for high pTRAA, v2{2}, v3{2}, and v2{4} in PbPb collisions at sNN=5.02 TeV. With an order of magnitude larger statistics we find that high pT elliptic flow does not scale linearly with the soft elliptical flow, as originally thought, but has deviations from perfectly linear scaling. A new experimental observable, which involves the difference between the ratio of harmonic flow cumulants at high and low pT, is proposed to investigate the fluctuations of high pT flow harmonics and measure this nonlinear response. By varying the path length dependence of the energy loss and the viscosity of the evolving medium we find that RAA(pT) and v2{2}(pT) strongly depend on the choice for the path length dependence of the energy loss, which can be constrained using the new LHC run 2 data.