Hierarchy of Azimuthal Anisotropy Harmonics in Collisions of Small Systems from the Color Glass Condensate

Abstract

We demonstrate that the striking systematics of two-particle azimuthal Fourier harmonics v_{2} and v_{3} in ultrarelativistic collisions of protons, deuterons, and helium-3 ions off gold nuclei measured by the PHENIX Collaboration at the Relativistic Heavy Ion Collider (RHIC) is reproduced in the color glass condensate effective field theory. This contradicts the claim in C. Aidala et al. (PHENIX Collaboration), arXiv:1805.02973, that their data rule out initial state-based explanations. The underlying systematics of the effect, as discussed previously in K. Dusling, M. Mace, R. Venugopalan, Phys. Rev. D 97, 016014 (2018)PRVDAQ2470-001010.1103/PhysRevD.97.016014; Phys. Rev. Lett. 120, 042002 (2018)PRLTAO0031-900710.1103/PhysRevLett.120.042002; Proc. Sci., QCDEV2017 (2018) 039, arise from the differing structure of strong color correlations between gluon domains of size 1/Q_{S} at fine (p_{⊥}⪆Q_{S}) or coarser (p_{⊥}⪅Q_{S}) transverse momentum resolution. Further tests of the limits of validity of this framework can be carried out in light-heavy ion collisions at both RHIC and the Large Hadron Collider. Such measurements also offer novel opportunities for further exploration of the role of the surprisingly large short-range nuclear correlations measured at Jefferson Lab.

What does the matter created in high multiplicity proton-nucleus collisions teach us about the 3-D structure of the proton?

“…While such effects are certainly there, there are open issues remaining whether they can be expressed as the generalized transverse momentum dependent (G-TMD) expressions as suggested in [77,76] and what their impact on the results are. At any rate, these effects should be contained in the full Yang-Mills computation alluded to previously [58,59]. Preliminary computations in the Yang-Mills framework suggest that the results are similar to those discussed here.…”

“…(The same problem bedevils event-by-event hydrodynamic computations of multiparticle correlations in pA collisions.) Very recent developments suggest however a considerable simplification to numerical solutions of the Yang-Mills equations that enable efficient computations of multiparticle azimuthal anisotropies [57]; these shall not be discussed at length any further but will be discussed separately [58,59].…”

Imaging the nucleus with high-energy photons

“…Despite the success of the hydrodynamical simulations and the hot spot picture, we note that there are other explanations for the azimuthal anisotropies seen in proton-nucleus collisions that do not rely on hydrodynamical evolution. For example, the Color Glass Condensate initial state description can produce the same systematic trends for the v n harmonic coefficients as observed in experiments [80]. Further, the applicability of hydrodynamics to small systems like those produced in proton-nucleus collisions is not yet completely established [81,82].…”

Elliptic flow in ultrarelativistic collisions with light polarized nuclei

“…Since these two color domains would contribute independently, forming a "double" p+A collision, the elliptic flow in d+A would be smaller than in p+A collisions, unlike in the experiment. The argument outlined above, however, was recently circumvented in [30][31][32], where contrary to naive expectations the highest multiplicity events in CGC correspond to configurations where the nucleons from the deuteron are one behind the other, which leads to larger saturation scales. See also the discussion in [33].…”