« Heavy quark observables of the Quark-Gluon Plasma produced in high energy heavy ion collisions. »
The six quarks and antiquarks are the fundamental bricks of matter that build up composite particles called hadrons. The most famous and stable of which are the protons and neutrons, the components of atomic nuclei. More unstable hadrons like the quarkonia (bound states of heavy quark and antiquark pairs) or open heavy mesons (bound states of heavy/light quark and antiquark pairs) can also be produced in high energy particle colliders (e.g. LHC).
Via the exchange of gluons, the strong interaction confines the quarks and antiquarks within the hadron and makes them impossible to be observed independently. The theory of elementary particles (Standard Model) predicts the existence of a new state of matter where the quarks and gluons are deconfined: the Quark-Gluon Plasma (QGP). The latter may have existed at the first moments of the Universe after the Big Bang and can, in theory, be re-produced in heavy ion collisions at high energy colliders.
Project 1 (Subatech, France): Quarkonia, QGP, open quantum systems
One of the QGP possible observables (and especially of its temperature) is the suppression of the quarkonia, i.e. a characteristic decrease of the detected amount of quarkonia in comparison to proton-proton collisions, in which no QGP production is possible. This suppression has indeed been observed experimentally, but is still poorly understood. Treating the heavy quark/antiquark pair as an open quantum system, we study its fate inside a hydrodynamic QGP, by considering its binding potential and energy exchanges.
Project 2 (University of São Paulo, Brazil): Open heavy flavors, coalescence, event-by-event engineering
Some other interesting observables are the suppression and flow of the open heavy mesons. The flow describes the collectivity of their motion in the plane transverse to the collision axis. The simultaneous description of these obervables has revealed to be a long standing puzzle. The project consists in building a state-of-the-art simulation that includes an event-by-event viscous hydrodynamic description of the QGP, an energy loss model for the heavy quark propagation, a fragmentation/coalescence process for their hadronisation… A special focus is given to event-by-event obervables and to the cumulant method for flow determination. We performed a system size scan at LHC energies with D mesons and showed that their flow is roughly equivalent regardless of system size in most central collisions.