Speakers
Description
Measurements of quarkonium-in-jet fragmentation have established that hidden heavy-flavor hadrons, such as $J/\psi$ ($c\bar c$) and $\Upsilon$ ($b\bar b$) states, are produced copiously within active jet showers. This has motivated new developments in parton shower algorithms, opening a broader avenue for heavy-flavor jet substructure studies. We present a comparative phenomenological study of quarkonium-tagged and double-open-heavy-flavor-tagged jets using the Lund jet plane. Events are simulated with Pythia8 for proton-proton collisions at LHC energies, using the recent OniaShowers module to generate quarkonium-tagged jets. The Lund jet plane resolves successive stages of the jet shower associated with heavy-flavor gluon splitting, from the gluon-rich cascade preceding the $g\to Q\bar Q$ splitting, to the splitting itself, the subsequent radiation of the heavy-quark antenna, and ultimately hadronization. Collinear emissions along the quarkonium-following prong are found to be strongly suppressed relative to the corresponding double-open-heavy-flavor case, reflecting the formation of color-singlet heavy-flavor bound states. Comparisons to a gluon-jet baseline are used to visualize mass effects in the collinear region and to provide a reference Casimir color factor in the hard, wide-angle region of the plane. $J/\psi$-tagged jets exhibit Lund plane densities compatible with the gluon-jet baseline for hard emissions, suggesting a possible path to test the radiative behavior of intermediate color-octet states in general. Overall, these studies show how quarkonium-tagged and double-open-heavy-flavor jets can jointly provide new insight into the overall radiation pattern associated to jet showers.