System-size dependence of the viscous attenuation of anisotropic flow in p + Pb and Pb + Pb collisions at energies available at the CERN Large Hadron Collider

The elliptic and triangular flow coefficients (vn,n=2,3) measured in Pb + Pb (sNN=2.76TeV) and p+Pb(sNN=5.02TeV) collisions are studied as a function of initial-state eccentricity (n) and dimensionless size characterized by the cube root of the midrapidity charged hadron multiplicity density (Nch)1/3. The results indicate that the influence of eccentricity (vnn) observed for large (Nch) is superseded by the effects of viscous attenuation for small (Nch), irrespective of the colliding species. Strikingly similar acoustic scaling patterns of exponential viscous modulation with a damping rate proportional to n2 and inversely proportional to the dimensionless size are observed for the eccentricity-scaled coefficients for the two sets of colliding species. The resulting scaling parameters suggest that, contrary to current predilections, the patterns of viscous attenuation as well as the specific shear viscosity ηs(T) for the matter created in p+Pb and Pb + Pb collisions are comparable.