Parton model description of multiparticle azimuthal correlations in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi><mml:mi>A</mml:mi></mml:math> collisions

Abstract

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 ${c}_{2}{4}$, which generates a real four-particle second Fourier harmonic ${v}_{2}{4}$; (ii) the ordering ${v}_{2}{2}&gt;{v}_{2}{4}\ensuremath{\approx}{v}_{2}{6}\ensuremath{\approx}{v}_{2}{8}$ 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 (${p}_{\ensuremath{\perp}}$) dependence of multiparticle azimuthal correlations. We find that the dependence of ${v}_{2}{2}$ and ${v}_{2}{4}$ on the number of color domains in the target varies with the ${p}_{\ensuremath{\perp}}$ window explored. We extend our prior discussion of symmetric cumulants and compute as yet unmeasured symmetric cumulants. We investigate the ${N}_{c}$ dependence of ${v}_{2}{2}$ and ${v}_{2}{4}$. 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 ${v}_{2}{4}$. We provide an algorithm to compute expectation values of arbitrary products of the ``dipole'' lightlike Wilson line correlators.