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arXiv · 1405.3605

Eccentric protons? Sensitivity of flow to system size and shape in p+p, p+Pb and Pb+Pb collisions

Bjoern Schenke·Raju Venugopalan
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Abstract

We determine the transverse system size of the initial non-equilibrium Glasma state and of the hydrodynamically evolving fireball as a function of produced charged particles in p+p, p+Pb and Pb+Pb collisions at the Large Hadron Collider. Our results are consistent with recent measurements of Hanbury-Brown-Twiss (HBT) radii by the ALICE collaboration. Azimuthal anisotropy coefficients v_n generated by combining the early time Glasma dynamics with viscous fluid dynamics in Pb+Pb collisions are in excellent agreement with experimental data for a wide range of centralities. In particular, event-by-event distributions of the v_n agree with the experimental data out to fairly peripheral centrality bins. In striking contrast, our results for p+Pb collisions significantly underestimate the magnitude and do not reproduce the centrality dependence of data for v_2 and v_3 coefficients. We argue that the measured v_n data and HBT radii strongly constrain the shapes of initial parton distributions across system sizes that would be compatible with a flow interpretation in p+Pb collisions. Alternately, additional sources of correlations may be required to describe the systematics of long range rapidity correlations in p+p and p+Pb collisions.

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Bjoern Schenke, Raju Venugopalan. 2014-05-14. Eccentric protons? Sensitivity of flow to system size and shape in p+p, p+Pb and Pb+Pb collisions. https://doi.org/10.1103/physrevlett.113.102301

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