Speaker
Description
Collider data shows that elliptic flow in high-multiplicity proton-nucleus and nucleus-nucleus collisions emerges as a response to the spatial ellipticity characterizing the energy density deposited in the transverse plane by the collision process. For collisions at small multiplicities, however, elliptic flow is expected to receive as well an important contribution from the anisotropic structures of the full energy-momentum tensor of the system, beyond the mere energy density. I show that, in the color glass condensate effective theory of high-energy QCD, these structures emerge from the correlation of gluon fields in the earliest stages of the collision, so that obtaining evidence of their manifestation in experiments is of the utmost importance. A recent study within the IP-Glasma+MUSIC+urQMD framework shows that signatures of these primordial anisotropies can be found experimentally in $v_2$-$\langle p_t \rangle$ correlations, whose sign at low multiplicities depends on whether or not the full structure of the IP-Glasma energy-momentum tensor is included in the simulations. I review these results, and use them to argue that the discovery of the primordial anisotropic flow of heavy-ion collisions is a simple matter of defining the right correlations that magnify its signatures.
