Sierra Cantway successfully defends thesis, "Probing jet hadrochemistry modification with measurements of identified particles in jets and the underlying event in pp and Pb–Pb collisions with ALICE"
On April 1, Sierra Cantway successfully defended the thesis “Probing jet hadrochemistry modification with measurements of identified particles in jets and the underlying event in pp and Pb–Pb collisions with ALICE” (advisor: Helen Caines).
Cantway explained, “My thesis focuses on understanding the strong force, one of the fundamental forces of the Universe. This force governs the interactions between quarks and gluons, which are elementary subatomic particles that, for instance, make up protons and neutrons. In particular, my thesis contributes to our understanding of two especially interesting aspects of the strong force: hadronization and the Quark-Gluon Plasma (QGP).”
“Hadronization is the process by which quarks and gluons combine to form composite particles called hadrons, which include protons and neutrons. The exact mechanism of how this occurs is unknown. In ordinary matter, quarks and gluons are confined to exist inside these hadrons. However, quarks and gluons exist freely outside of hadrons in the QGP, an exotic, high-energy-density state of matter. This state existed briefly just after the Big Bang and can now be recreated in high-energy collisions of heavy ions.”
Cantway continued, “My tools of choice to study both of these phenomena are identified particles—the different flavors of hadrons—and jets—narrow sprays of hadrons resulting from high momentum interactions of quarks and gluons. Specifically, my thesis measures how the flavors of identified particles vary in vs. out of jets and in the QGP vs. in vacuum. My thesis measurements provide the first indications of modified identified particle makeup of jets in the QGP compared to those of jets in vacuum, improving our understanding of jet-QGP interactions and hadronization.”
Cantway will continue to study jets in the QGP in her next position as a postdoctoral associate at the University of Illinois Urbana-Champaign, now in the ATLAS experiment.
Cantway added, “The Relativistic Heavy-Ion Group has been an amazing group of people not only to work with, but also to call my friends. I am so grateful for my time in this group, and I will miss seeing them all every day dearly.”
Thesis 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 π, 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 √(s_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.
Thesis committee: Helen Caines (advisor), Laura Havener, Ian Moult, Sarah Demers, Jana Bielčíková (Nuclear Physics Institute of the Czech Academy of Sciences)