Description du sujet de thèse

The proposed thesis concerns the study of jet quenching by measuring heavy flavor jets from data collected with the ALICE experiment during Run 3 of the Large Hadron Collider (LHC).
The aim of this PhD work is to elucidate the dependence of the jet quenching phenomenon on the flavor of the parton at the origin of the jet, by measuring and characterizing jets containing heavy flavors produced in high-energy heavy-ion collisions. The ultimate goal is to improve our understanding of the transport properties of quark-gluon plasma (QGP). Heavy quarks, such as the charm and beauty quarks, which give rise to heavy flavor jets, are indeed supposed to undergo a reduced energy loss due to the “dead-cone” effect. This phenomenon results from the quark's mass, which suppresses gluon emission at small angles, thus limiting radiation in a cone-shaped region around its direction of motion.
The ALICE detector has undergone major upgrades during the LHC's Long Shutdown 2 (LS2), strengthening its detection capabilities for Run 3. These improvements include upgrading the internal tracking system with new silicon pixel detectors and replacing the readout chambers of the Time Projection Chamber (TPC). In addition to a drastic increase in the data acquisition rate and, consequently, in the accumulated statistics, these enhancements provide better resolution on track momentum measurement, increased efficiency and improved particle identification, offering unrivalled accuracy for measurements of heavy flavor particles and jets.
By studying the behavior of heavy flavor jets produced in Pb–Pb collisions at the LHC, this thesis work will provide essential information on the mechanisms of parton energy loss in QGP, enabling us to gain a deeper understanding of QGP properties.
This research will enhance our understanding of QGP and the strong interaction, with wider implications for high-energy nuclear physics and potential technological spin-offs from detector improvements. The project will involve close collaboration with members of the ALICE team at LPSC and may benefit from inter-institutional partnerships, supported by computing resources and software tools for data analysis and simulations. The planned timetable extends over three years, starting with a review of the literature and theoretical studies, followed by data analysis and algorithm development, and concluding with model refinement, finalization of results and writing of the thesis.

- Activities will focus on jet reconstruction and flavor labeling using advanced machine learning techniques, such as deep learning algorithms for secondary vertex reconstruction and boosted decision trees for displaced trace identification.
- Experimental results will then be compared with theoretical models and simulations. In addition to standard observables such as transverse impulse spectra or fragmentation functions, original substructure observables may be introduced, such as the opening angle or the transverse impulse distribution between 2 subjets.
- The successful candidate will also contribute to the innovative ITS3 upgrade of the ALICE experiment's internal trajectography system (ITS), using state-of-the-art monolithic active pixel sensor (MAPS) technology. The ITS3 detector, made up of three truly cylindrical layers of large MAPS sensors in 65 nm technology, will significantly enhance the ALICE experiment's physics capabilities for Run 4. This upgrade will improve measurements of heavy flavor mesons and baryons, providing valuable information on the interaction of charm and beauty quarks as they pass through the plasma.

Contexte de travail

The Grenoble Laboratory of Subatomic Physics and Cosmology (LPSC) (http://lpsc.in2p3.fr) is a joint research unit associating CNRS-IN2P3, Université Grenoble Alpes (UGA) and Grenoble INP school, for an average staff of around 230.
The PhD student will be assigned́ to the ALICE research group, comprising 4 researchers and teacher-researchers, 1 post-doc and 1 PhD student.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.