Parton model description of multiparticle azimuthal correlations in pA collisions

Kevin Dusling (American Physical Society, 1 Research Road, Ridge, New York 11961, USA; Physics Department, Brookhaven National Laboratory, Bldg. 510A, Upton, New York 11973, USA) ; Mark Mace (Physics Department, Brookhaven National Laboratory, Bldg. 510A, Upton, New York 11973, USA; Physics and Astronomy Department, Stony Brook University, Stony Brook, New York 11974, USA) ; Raju Venugopalan (Physics Department, Brookhaven National Laboratory, Bldg. 510A, Upton, New York 11973, USA)

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.

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      "value": "In K. Dusling et al. [arXiv:1705.00745.], an initial-state \u201cparton model\u201d 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 (<math><mi>p</mi><mi>A</mi></math>) collisions at the Relativistic Heavy Ion Collider and the LHC. The systematics included (i) the behavior of the four-particle cumulant <math><msub><mi>c</mi><mn>2</mn></msub><mo>{</mo><mn>4</mn><mo>}</mo></math>, which generates a real four-particle second Fourier harmonic <math><msub><mi>v</mi><mn>2</mn></msub><mo>{</mo><mn>4</mn><mo>}</mo></math>; (ii) the ordering <math><msub><mi>v</mi><mn>2</mn></msub><mo>{</mo><mn>2</mn><mo>}</mo><mo>&gt;</mo><msub><mi>v</mi><mn>2</mn></msub><mo>{</mo><mn>4</mn><mo>}</mo><mo>\u2248</mo><msub><mi>v</mi><mn>2</mn></msub><mo>{</mo><mn>6</mn><mo>}</mo><mo>\u2248</mo><msub><mi>v</mi><mn>2</mn></msub><mo>{</mo><mn>8</mn><mo>}</mo></math> 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 (<math><msub><mi>p</mi><mo>\u22a5</mo></msub></math>) dependence of multiparticle azimuthal correlations. We find that the dependence of <math><msub><mi>v</mi><mn>2</mn></msub><mo>{</mo><mn>2</mn><mo>}</mo></math> and <math><msub><mi>v</mi><mn>2</mn></msub><mo>{</mo><mn>4</mn><mo>}</mo></math> on the number of color domains in the target varies with the <math><msub><mi>p</mi><mo>\u22a5</mo></msub></math> window explored. We extend our prior discussion of symmetric cumulants and compute as yet unmeasured symmetric cumulants. We investigate the <math><msub><mi>N</mi><mi>c</mi></msub></math> dependence of <math><msub><mi>v</mi><mn>2</mn></msub><mo>{</mo><mn>2</mn><mo>}</mo></math> and <math><msub><mi>v</mi><mn>2</mn></msub><mo>{</mo><mn>4</mn><mo>}</mo></math>. 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 <math><msub><mi>v</mi><mn>2</mn></msub><mo>{</mo><mn>4</mn><mo>}</mo></math>. We provide an algorithm to compute expectation values of arbitrary products of the \u201cdipole\u201d lightlike Wilson line correlators."
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Published on:
25 January 2018
Publisher:
APS
Published in:
Physical Review D , Volume 97 (2018)
Issue 1
DOI:
https://doi.org/10.1103/PhysRevD.97.016014
arXiv:
1706.06260
Copyrights:
Published by the American Physical Society
Licence:
CC-BY-4.0

Fulltext files: