Access the emergence of hydrodynamics with dileptons – AccessEmergence

Collisions between two heavy ions in particle colliders allow us to study the properties of strongly interacting matter with high energy density. Such collisions create small systems with up to a few thousand produced particles which are found to behave as fluids with remarkable properties.
The experimental results suggest that hydrodynamic behaviour emerges on a rather short time scale, a feature that is theoretically not well understood. In order to obtain direct information on the early stages of the matter evolution which precede the hydrodynamic phase, we propose to measure the production of dileptons (electron-positron or muon-antimuon pairs) in these collisions in the mass range of 1-5 GeV/c². These are indeed preequilibrium processes and could shed light on the mechanism that lead to thermalisation.
These dileptons have not yet been observed because they are hidden under a large background coming from the decays of charm and beauty hadrons. In addition, at high masses dileptons are produced directly from the initial wave functions of the incoming nuclei by the so-called Drell-Yan process.
The LHC beauty (LHCb) experiment has been constructed especially to detect charm and beauty hadrons in proton-proton collisions. Its currently installed upgrade is designed to handle a larger number of particles such as produced in heavy-ion collisions. This provides a unique opportunity to perform the first measurement of dileptons with m within 1-5 GeV/c² in heavy-ion collisions.
Based on my experience and leadership on muon and electron measurements in two LHC collaborations, I will build a team to measure the Drell-Yan background in pp collisions and to study the feasibility to access experimentally the equilibration process in heavy-ion collisions with dileptons.