Laboratory link : https://irfu.cea.fr/dphn/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=500
More : https://home.cern/fr/science/experiments/lhcb
Heavy-ion collisions are the golden system to study the quark-gluon plasma (QGP), an exotic state of matter that presumably existed few microseconds after the Big Bang. Among the probes to study the QGP, the production of hadrons containing charm quark (e.g D0 mesons) is one of the historical smoking guns. Indeed, being produced in the very first stages of the collisions, these particles keep track of their subsequent interactions with the QGP. In particular, the study of simultaneous double charm production, never carried out in ion-ion collisions at the LHC, could shed a light on the transport properties of the QGP.
At the end of 2023, the LHCb collaboration will record high energy Pb-Pb collisions at the LHC. These data will benefit from the latest LHCb upgrades which offer enhanced detector capabilities. Notably, the new tracking system of this heavy-quark dedicated detector will allow us to cope with the high detector occupancy in ion-ion collisions. This combined with an increase of the data sample by a factor of two will provide the best Pb-Pb data recorded by the collaboration so far.
Finally, a new upgrade phase of the detector is scheduled for 2030 for which new tracker projects are developed. Among the new detectors, the Upstream Tracker (UT) is the key to reduce the rate of fake tracks reconstructed in head-on ion-ion collisions and ensure good data quality for LHCb heavy-ion program. The development of the UT has started, but the final design is still to be defined. In addition, sophisticated tracking algorithms based on machine learning could be developed to fully exploit the detector future capabilities. Not only this work could improve further the LHCb tracking efficiency in ion data, but also in regular proton-proton collisions, which is at the heart of the collaboration physics program.
# Research project
The PhD research project is divided in two main parts:
- Study of the double charm cross-section in Pb-Pb data with LHCb: this objective implies the participation to the 2023 ion data-taking, the extraction of the signal in these data, and the study of uncertainties using simulations. The study could follow what was done previously by the collaboration with other data sets, but more specific studies to ion-ion collisions will be done in close relationship with the theory community.
- Participation to the UT project: this objective focuses on the development of a new tracking algorithm. In particular, the usage of the Graph Neural Network to the LHCb tracking strategy will be explored to improve both efficiency and computing performance.