Closepacking effects on strangeness and baryon production at the LHC

Abstract: Data from the LHC show a rise in strange-hadron production with charged-particle multiplicity in pp collisions. The Monte-Carlo event generator PYTHIA, using its default Monash tune, instead predicts constant strangeness. We investigate a mechanism invoked during hadronization called string closepacking, where overlapping strings generate a background field, here assumed to be predominantly aligned with the beam axis. This increases the effective string tension with rapidity, reducing strangeness suppression and thus enhancing strangeness production. We tune this model to LHC data and contrast it with several alternatives. We comment specifically on the challenge of simultaneously describing the strangeness data and the non-strange p/pi ratio, and introduce a mechanism which may act to suppress the latter. Many of the salient particle-production ratios can be qualitatively described by this model, although the XiC/D ratio and the shape of pT spectra remain challenging to account for.