  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.
