High Multiplicity pp and pA Collisions: Hydrodynamics at its Edge and Stringy Black Hole
High Multiplicity pp and pA Collisions is a place where the macroscopic description (thermo and hydrodynamics) meets with the microscopic one (pomerons and QCD strings). In the first part of the paper we study what happens with the hydrodynamical predictions as the system size gets smaller and smaller. For simplicity, we don't do it numerically, but analytically using Gubser$^′$ s flow. We found that the radial flow is expected to increase, while the elliptic flow decreases, and high harmonics become perhaps too small to be observed. In the second part of the paper we approach the problem from the opposite side, using a string-based Pomeron model. We found that as the intrinsic temperature of the string grows, it approaches the Hagedorn regime and produces a high entropy string ball, amusingly dual to a certain black hole. Furthermore, when the string temperature narrows on the Hagedorn temperature or $T/T_H-1=\cal O(1/N_c)$, the stringy ball becomes a sQGP ball with non-negligible pressure and hydrodynamical flow.