Abstract
The striking similarities that have been observed between high-multiplicity proton-proton (pp) collisions and heavy-ion collisions can be explored through multiplicity-differential measurements of identified hadrons in pp collisions. With these measurements, it is possible to study mechanisms such as collective flow that determine the shapes of hadron transverse momentum (pT) spectra, to search for possible modifications of the yields of short-lived hadronic resonances due to scattering effects in an extended hadron-gas phase, and to investigate different explanations provided by phenomenological models for enhancement of strangeness production with increasing multiplicity. In this paper, these topics are addressed through measurements of the K⁎(892)0 and ϕ(1020) mesons at midrapidity in pp collisions at s= 13 TeV as a function of the charged-particle multiplicity. The results include the pT spectra, pT-integrated yields, mean transverse momenta, and the ratios of the yields of these resonances to those of longer-lived hadrons. Comparisons with results from other collision systems and energies, as well as predictions from phenomenological models, are also discussed.
Highlights
Recent studies of proton-proton and proton-lead (p–Pb) collisions at the LHC with high charged-particle multiplicities have shown patterns of behavior that are reminiscent of phenomena observed in heavy nucleus-nucleus (A–A) collisions such as Pb–Pb and Xe–Xe
The systems created in these collisions are compared by classifying events according to the final-state charged-particle multiplicity, which is used as a measure of the “activity” of the event
The observed enhancement of strange hadron production [8,9,12] could indicate the production of a quark–gluon plasma (QGP), while the possible suppression of the yields of short-lived resonances [8,11] may suggest the presence of an extended hadronic phase
Summary
Recent studies of proton-proton (pp) and proton-lead (p–Pb) collisions at the LHC with high charged-particle multiplicities have shown patterns of behavior that are reminiscent of phenomena observed in heavy nucleus-nucleus (A–A) collisions such as Pb–Pb and Xe–Xe. The larger and denser collision systems form color ropes [29,30,31], groups of overlapping strings that hadronize with a larger effective string tension This effect, implemented in models such as DIPSY [32,33,34], leads to an increase in the production of strange hadrons with increasing charged-particle multiplicity. It was observed that the slopes of hadron pT spectra increase with increasing multiplicity in pp and p–Pb collisions [8,9,10,11], while an enhancement in pT-differential baryonto-meson ratios (e.g. p/π and /K0S ) is observed at intermediate pT (2 pT 7 GeV/c) This is at least qualitatively similar to the behavior observed in Pb–Pb collisions [51,52,53,54], where the effects can be attributed to a collective expansion of the system.
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