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 c₂4, which generates a real four-particle second Fourier harmonic v₂4; (ii) the ordering v₂2>v₂4≈v₂6≈v₂8 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 v₂2 and v₂4 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 v₂2 and v₂4. 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 v₂4. We provide an algorithm to compute expectation values of arbitrary products of the ``dipole'' lightlike Wilson line correlators.