Parton model description of multiparticle azimuthal correlations in p A collisions

In [1], an initial state “parton model” of quarks scattering off a dense nuclear target was shown to qualitatively reproduce the systematics of multiparticle azimuthal anisotropy cumulants measured in proton/deuteron-nucleus (pA) collisions at RHIC and the LHC. The systematics included i) the behavior of the four-particle cumulant c2{4}, which generates a real four-particle second Fourier harmonic v2{4}, ii) the ordering v2{2} > v2{4} ≈ v2{6} ≈ v2{8} for two-, four-, six-, and eight-particle Fourier harmonics, iii) the behavior of so-called symmetric cumulants SC(2,3) and SC(2,4). These features of azimuthal multiparticle cumulants were previously interpreted as a signature of hydrodynamic flow; our results challenge this interpretation. We expand here upon our previous study and present further details and novel results on the saturation scale and transverse momentum (p⊥) dependence of multiparticle azimuthal correlations. We find that the dependence of v2{2} and v2{4} on the number of color domains in the target varies with the p⊥ window explored. We extend our prior discussion of symmetric cumulants and compute as yet unmeasured symmetric cumulants. We investigate the Nc dependence of v2{2} and v2{4}. We contrast our results, which include multiple scatterings of each quark off the target, to the Glasma graph approximation, where each quark suffers at most two gluon exchanges with the target. We find that coherent multiple scattering is essential to obtain a positive definite v2{4}. We provide an algorithm to compute expectation values of arbitrary products of the “dipole” lightlike Wilson line correlators.