The role of the underlying event in the charmed-baryon enhancement in high-energy pp collisions

May 16, 2022, 3:10 PM


Zoltan Varga (Wigner RCP)


The production of heavy-flavor hadrons is usually described using the factorization hypothesis, in
which the production cross section is expressed as convolutions of three independent factors: the
parton distribution functions (PDF) of the colliding hadrons, the production cross-sections of the
heavy-quarks in the hard partonic process, and the fragmentation functions of the heavy-quarks into
the given heavy-flavor hadron species. Fragmentation has been widely regarded as being universal,
that is, independent of the collision system.
Charmed-baryon to meson ratios recently measured by ALICE and CMS at the LHC, however,
show a low-momentum enhancement over model predictions based on e+ -- e- collisions,
suggesting that universality is not fulfilled [1,2]. Furthermore, recent measurements showed that
this enhancement depends on the final-state multiplicity [3]. Several scenarios, based on string
formation beyond leading order, an augmented set of charm baryon states, or quark coalescence in
p--p collisions provide qualitative descriptions to these findings.
In this contribution we investigate the enhanced production of charmed baryons relative to charmed
mesons in proton--proton collisions at LHC energies utilizing PYTHIA 8 simulations with enhanced
color-reconnection. We proposed methods based on the comparative use of several event-activity
classifiers to identify the source of the charmed-baryon enhancement. We concluded that in the
investigated models the excess Λc production is primarily linked to the underlying event activity
and not to the production of jets. [4] We provide predictions for ratios of further charmed-baryon to
baryon and meson states to understand the role of strangeness and charm in the enhancement. The
proposed event-activity-differential observables, when utilized on data from the upcoming LHC
Run 3, will provide high selectivity and valuable input for model development.
[1] CMS Coll., Phys. Lett. B 803 (2020) 135328, arXiv:1906.03322.
[2] ALICE Coll., Physicial Review Letters 127, 202301 (2021), arXiv:2011.06078.
[3] ALICE Coll., CERN-EP-2021-245, arXiv:2111.11948.
[4] Z. V., R. V., arXiv:2111.00060, Submitted to J.Phys.G.

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