The understanding of heavy ion collisions and its quark-gluon plasma (QGP) formation requires a complicated interplay of rich physics in a wealth of experimental data. In this work we compare for identified particles the transverse momentum dependence of both the yields and the anisotropic flow coefficients for both PbPb and $p\mathrm{Pb}$ collisions. We do this in a global model fit including a free streaming prehydrodynamic phase with variable velocity $v_{\mathrm{fs}}$, thereby widening the scope of initial conditions. During the hydrodynamic phase we vary three second order transport coefficients. The free streaming velocity has a preference slightly below the speed of light. In this extended model the QGP bulk viscosity is small and even consistent with zero.

• Received 5 November 2020
• Revised 26 February 2021
• Accepted 12 April 2021

DOI:https://doi.org/10.1103/PhysRevLett.126.202301

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society