Probing flavor effects in the QCD parton shower using ${\mathrm{D}}^0$-tagged jet angularities in proton$-$proton collisions at $\sqrt{\mathbf{s}}=5.02$ TeV

Abstract

The ALICE Collaboration presents the first measurements of ${\mathrm{D}}^0$-tagged jet angularities in proton$-$proton (pp) collisions at $\sqrt{s}=5.02$ TeV. Jet angularities are powerful substructure observables that characterize the angular and momentum distributions of particles within jets via tunable weighting parameters. Varying the angular parameter in jet angularities allows for a systematic probe of the sensitivity to collinear and soft radiation, enabling the study of flavor-dependent fragmentation and hadronization through comparisons of jets initiated by different partons. This paper reports ${\mathrm{D}}^0$-tagged and inclusive (gluon-dominated) charged-particle jet angularities with a resolution parameter $R=0.4$ in the low jet transverse momentum range ($10<p_{\mathrm{T}}^{ch.\mathrm{jet}}<20$ GeV/$c$), where charm-quark mass effects are most significant. At low angular weight, which emphasizes collinear radiation, ${\mathrm{D}}^0$-tagged jets exhibit smaller angularity values than inclusive jets. This provides evidence for the radiation suppression from massive quarks -- a phenomenon known as the QCD dead-cone effect. As the angular weight increases, giving more emphasis to wide-angle radiation, the difference between ${\mathrm{D}}^0$-tagged and inclusive jet distributions decreases. This indicates that the modification is concentrated within the jet core rather than its edge. PYTHIA 8 simulations qualitatively reproduce both the angularity of ${\mathrm{D}}^0$-tagged and inclusive charged-particle jets, but reproduce the ${\mathrm{D}}^0$-tagged jet distributions better than those of inclusive jets, offering a powerful new constraint for models. These results provide insight into flavor-dependent fragmentation and establish an essential baseline for future studies of jet modifications in the quark-gluon plasma produced in heavy-ion collisions.

Comments: 24 pages, 6 captioned figures, 1 table, authors from page 19, submitted to PRD, figures at http://alice-publications.web.cern.ch/node/13375