Alex Jentsch, UT-Austin

"Studying Heavy-Flavor Quark Jets Using D0-Hadron Two-Dimensional Angular Correlations in Au+Au Collisions at 200 GeV"

Abstract: The study of Quantum Chromodynamics (QCD) in conditions of extreme temperature and energy density has been accomplished over the past two decades using heavy-ion collisions at the Relativistic heavy-ion Collider (RHIC). Recently, the addition of the Heavy Flavor Tracker from 2014-2016 has granted the STAR experiment the ability to precisely reconstruct decay-vertices of secondary particles separated from the primary collision vertex by $sim 30 mu m$. This enables the direct reconstruction of heavy-flavor quark (e.g. charm, bottom) mesons, which are useful for studying the hot and dense medium - known as the Quark-Gluon Plasma (QGP) - formed in heavy-ion collisions. Heavy-flavor quarks are useful for studying the QGP because they are formed in hard-scattering interactions that take place before the formation of the medium and then hadronize and decay outside the medium. This makes heavy-quarks sensitive to the entire evolution of the QGP, and therefore an ideal probe for its study.

In this analysis, correlations on relative azimuth and pseudorapidity between a charm-containing meson ($D^0$) and all other charged hadrons are presented. In particular, the near-side ($Deltaphi < frac{pi}{2}$) jet-like peak is studied, with the $D^{0}$ serving as a proxy for charm-jet. Using a multi-parameter fit-model with no underlying physics assumptions, the widths and associated yield of the near-side peak are studied as a function of centrality. The evolution of this near-side correlation structure yields insight into the charm-jet interactions with the partonic medium.

These results are compared to PYTHIA and a trigger-associated light-flavor correlation analysis. The results imply significant interaction of the charm-quark with the medium via gluon radiation and collisions with neighboring partons, similar to what is observed for light-flavor correlations at a similar transverse momentum. Model predictions for heavy-ion collisions that include charm are needed for further understanding of these measurements.