Gluonic hot spot initial conditions in heavy-ion collisions

The initial conditions in heavy-ion collisions are calculated in many different frameworks. The importance of nucleon position fluctuations within the nucleus and subnucleon structure has been established when modeling initial conditions for input to hydrodynamic calculations. However, there remain outstanding puzzles regarding these initial conditions, including the measurement of the near equivalence of the elliptical v(2) and triangular v(3) flow coefficients in ultracentral 0-1% Pb+Pb collisions at the CERN Large Hadron Collider. Recently a calculation termed magma incorporating gluonic hot spots via two-point correlators in the color glass condensate framework, and no nucleons, provided a simultaneous match to these flow coefficients measured by the ATLAS experiment, including in ultracentral 0-1% collisions. Our calculations reveal that the magma initial conditions do not describe the experimental data when run through full hydrodynamic sonic simulations or when the hot spots from one nucleus resolve hot spots from the other nucleus, as predicted in the color glass condensate framework. We also explore alternative initial condition calculations and discuss their implications.

Automated summary

Initial conditions in heavy-ion collisions are calculated in various frameworks, with a focus on nucleon position fluctuations and subnucleon structure. However, there are outstanding puzzles regarding these initial conditions, including the measurement of flow coefficients. Recent magma calculations incorporating gluonic hot spots in the color glass condensate framework match experimental results but do not fully describe the data, prompting further exploration of alternative initial condition calculations and their implications.