Welcome to QCD challenges at LHC Guy Paic

Are we near to a breakthrough? The body of data will probably bring many new insights into the system of quarks and gluons in collisions. There are many questions that necessitates explanation and understanding. From the long range plane 2015 “horizon 2020”: the emergent phenomenon that a macroscopic volume of quarks and gluons at extreme temperatures would form a nearly perfect liquid came as a complete surprise and has led to an intriguing puzzle. A perfect liquid would not be expected to have particle excitations, yet QCD is definitive in predicting that a microscope with sufficiently high resolution would reveal quarks and gluons interacting weakly at the shortest distance scales within QGP.

How to understand sQGP We coined this strange term to fulfill what? What do we understand by that? Interaction of strings like in MPI with color reconnection in pp collisions or some other. We observe “perfect fluid” as a result of “something” but we do not know the details of the interaction. We observe collective phenomena but these can have various origins

Is hydro the end word? In the following slides I will show on some examples what I see as the limitations of hydro. Talking with many hydro practioners I have gotten the impression that the community is aware of the incompleteness

M. Luzum (IS2014) It’s difficult to prove a theory is correct. The best one can do is try to disprove it, and failing that, look for other explanations that might be just as successful and more compelling

The limited range of the hydro fits The range of success is limted

Anysotropy at very central evts

Two important ingredients of the fits η/S and the initial state configuration

The extent of the anisotropy is much farther then the reach of the hydro fits

May the workshop contribute to the understanding Discussing the essence of the problems Concentrating on the differences rather than on where the “theory “qualitatively” fits the data.