Baryon-to-meson ratios in the Lund jet plane: resolving string-junction and thermal-fragmentation effects

Abstract

Baryon-to-meson ratios inside charged jets are studied in the Lund jet plane using PYTHIA simulations of pp collisions at $\sqrt{s} = 14$ TeV, with 15 < $p_{\rm T}^{\rm ch,jet}$ < 30 GeV/$c$ in an acceptance compatible with the future ALICE 3 detector. Jets are reclustered with the Cambridge--Aachen algorithm and identified hadrons are tagged at the splitting where they first separate from the leading branch. Three model configurations are compared: Monash, color reconnection beyond leading color (CR-BLC), and CR-BLC combined with thermodynamical string fragmentation (Thermal+CR-BLC). The $Λ_c^+/{\rm D}^0$ ratio rises with $\log(1/z)$ in the two configurations that include color-string junctions and is approximately flat under Monash. The same trend is present at the first Cambridge--Aachen branching, indicating that the effect is set at the level of the color topology rather than through the cumulative action of many soft splittings. Light- and strange-sector ratios show no $z$-dependent signature of either mechanism, but the angular projection reveals non-trivial structure at the first branching that is washed out when emissions are summed. The Cambridge--Aachen declustering and the Lund plane together separate the kinematic signatures of the two baryon-enhancement mechanisms in PYTHIA and provide observables accessible to future ALICE 3 measurements.