A scaling relation between proton-nucleus and nucleus-nucleus collisions

It is recently discovered that at high multiplicity, the proton-nucleus (pA) collisions give rise to two particle correlations that are strikingly similar to those of nucleus-nucleus (AA) collisions at the same multiplicity, although the system size is smaller in pA. Using an independent cluster model and a simple conformal scaling argument, where the ratio of the mean free path to the system size stays constant at fixed multiplicity, we argue that flow in pA emerges as a collective response to the fluctuations in the position of clusters, just like in AA collisions. With several physically motivated and parameter free rescalings of the recent LHC data, we show that this simple model captures the essential physics of elliptic and triangular flow in pA collisions.