Advisor: Helen Caines
Degree Year: 2026
Dissertation Title: Probing jet hadrochemistry modification with measurements of identified particles in jets and the underlying event in pp and Pb–Pb collisions with ALICE
Dissertation Abstract: The features of quantum chromodynamics (QCD) - the theory of the strong force - suggest that at sufficiently high energies or densities, quarks and gluons enter a deconfined state of matter called the quark-gluon plasma (QGP). The QGP is formed when heavy ions collide at relativistic energies, making the study of these collisions a great way to explore new regimes of QCD experimentally. Energetic partons produced early in the collisions lose energy in the QGP medium as it evolves. They then fragment and hadronize into showers of particles called jets. Measurements of the modification of the properties of these jets compared to vacuum are capable of revealing the nature of the QGP and how partons interact with it. Jet quenching models predict that the jet hadrochemical composition is modified in the QGP, arising from both modified jet fragmentation and the response of the medium to a jet passing through it. Although significant progress has been made in particle-species-inclusive jet measurements, a complete understanding of identified particle production inside jets (jet hadrochemistry) and its potential modification in the QGP remains elusive. Measurements of jet hadrochemistry help discriminate between proposed jet-medium interaction mechanisms.
Leveraging the excellent particle identification (PID) capabilities of the ALICE detector at the LHC, this thesis will discuss the first measurements of $\pi$, K, and p ratios within charged-particle-jets and the underlying event as a function of particle transverse momentum in pp and Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}$=5.02 TeV. In pp, it is observed that baryon and strangeness production in jets is lower than that of the inclusive event, and their production in jets is well described by fragmentation-dominated hadronization models. In Pb–Pb, the measurement shows hints of lower baryon and strangeness production in jets compared to the underlying event. While further quantitative comparison with theoretical models is required to constrain the relative effects of modified jet fragmentation and medium response, the enhanced baryon and strangeness production seen in Pb–Pb jets compared to pp jets provide the first hints of jet hadrochemistry modifications in heavy-ion collisions.
Information updated 04/06/2026
