Parton model description of multiparticle azimuthal correlations in pA collisions

In K. Dusling et al. [arXiv:1705.00745.], 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 the Relativistic Heavy Ion Collider 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; and (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.