Different patterns for different selections
A particle-physics preprint reports that charm baryons and mesons do not follow the same pattern when the event selection changes. The modeled ratios differed when charm resonances were found inside jets, narrow particle groupings used in the analysis, rather than in inclusive events. Baryon-to-meson ratios also varied with relative transverse activity, a count-based measure of charged particles in a transverse region. By contrast, D+/D0 and D*+/D0 were reported as independent of underlying-event activity in the SC-CR analysis. The Λc+/D0 ratio showed a reported dependence on event multiplicity.
This is a generator study. Pythia 8.312 produced predictions with two hadronisation settings, SC-CR and BLC-CR + Ropes, with simulation uncertainty shown around the predictions. Those outputs were compared with ALICE measurements of prompt charm-hadron ratios in proton-proton collisions at 13 TeV and central rapidity, |y| < 0.5. The question was how local jet conditions and global event conditions relate to the ratios, with particular attention to baryon-versus-meson behavior.
Inside the jet
For the jet part of the analysis, anti-kT jets were selected with a radius of R = 0.4, |ηJ| < 0.5 and transverse momentum of 7 < pTJ < 15 GeV/c. Charm hadrons were restricted to |yH| < 0.8 and 3 < pTH < 15 GeV/c. The study then compared normalized z|| distributions, using a momentum-sharing variable bounded from 0 to 1.
Those jet distributions were reproduced very well overall. The main mismatch was a small underestimation of D0 near the high end, at z|| approximately 1. But the ratio comparisons changed when charm resonances were required to be inside jets. For baryon-to-meson ratios, the differences were concentrated at low transverse momentum; for D+/D0 and D*+/D0, they were mainly visible between 1 and 7 GeV/c.
Sorting the wider event
Global event activity was examined with relative transverse activity, or RT. The selection required a leading particle with 8 < pLT < 15 GeV/c. The RT count used primary charged particles with pT > 0.5 GeV/c and |η| < 0.8 in the transverse region, while excluding charm-hadron decay products.
The resulting pattern split along the baryon-meson line. Baryon-to-meson ratios showed an important dependence on RT, while D+/D0 and D*+/D0 were reported as independent of underlying-event activity in the SC-CR analysis. The authors interpret this pattern as consistent with multiple-parton interactions, or MPI, and color reconnection for baryons, while the meson results are described as consistent with independent fragmentation. These are proposed mechanisms within the model interpretation of the curves.
A broad match with important boundaries
Across the main comparisons, both implementations were described as reproducing the data well overall. That agreement came with a model-specific problem: BLC-CR + Ropes overestimated the Sigma-c-to-D-zero ratio. The paper therefore points to a broad match alongside differences tied to the selection used, including inclusive, jet-contained, multiplicity-selected and relative-transverse-activity events.
The conclusions are tied to the stated simulation and comparison conditions. The authors' explanations remain model-based interpretations of the reported patterns, rather than measurements of an independently established mechanism. The study's central contribution is a picture of how the generator behaves under different jet, multiplicity and event-activity selections.
The document is an arXiv v1 preprint dated 25 Aug 2026. The authors acknowledge substantial computing resources from ACARUS at the Universidad de Sonora.
Paper data and sources
Original title: Impact of local and global event conditions in prompt charm hadron ratios
Authors: Luis Carlos Cruz Peralta, Lizardo Valencia Palomo
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-25
DOI: Not available
Original paper · Full text