Enhanced production of multi-strange hadrons in high-multiplicity proton–proton collisions

Abstract

At su ciently high temperature and energy density, nuclear matter undergoes a transition to a phase in which quarks and gluons are not confined: the quark-gluon plasma (QGP) 1 . Such an exotic state of strongly interacting quantum chromodynamics matter is produced in the laboratory in heavy nuclei high-energy collisions, where an enhanced production of strange hadrons is observed 2-6 . Strangeness enhancement, originally proposed as a signature of QGP formation in nuclear collisions 7 , is more pronounced for multi-strange baryons. Several e ects typical of heavy-ion phenomenology have been observed in high-multiplicity proton-proton (pp) collisions 8,9 , but the enhanced production of multi-strange particles has not been reported so far. Here we present the first observation of strangeness enhancement in high-multiplicity proton-proton collisions. We find that the integrated yields of strange and multi-strange particles, relative to pions, increases significantly with the event charged-particle multiplicity. The measurements are in remarkable agreement with the p-Pb collision results 10,11 , indicating that the phenomenon is related to the final system created in the collision. In high-multiplicity events strangeness production reaches values similar to those observed in Pb-Pb collisions, where a QGP is formed.The production of strange hadrons in high-energy hadronic interactions provides a way to investigate the properties of quantum chromodynamics (QCD), the theory of strongly interacting matter. Unlike up (u) and down (d) quarks, which form ordinary matter, strange (s) quarks are not present as valence quarks in the initial state, yet they are sufficiently light to be abundantly created during the course of the collisions. In the early stages of high-energy collisions, strangeness is produced in hard (perturbative) 2 → 2 partonic scattering processes by flavour creation (gg → ss, qq → ss) and flavour excitation (gs → gs, qs → qs). Strangeness is also created

Baryon production from cluster hadronisation

“…Again we point out the interplay between baryonic colour reconnection and the strangeness production mechanism which is responsible for the improvement in the description of the heavy baryons and − . In a recent analysis by ALICE a significant enhancement of strange to non-strange hadron production with increasing particle multiplicity in pp collisions was observed [6]. Since we are developing a model that incorporates strangeness production and the enhanced production of baryons it is instructive to compare our model to the data published by the ALICE collaboration.…”

“…Among the problems that are being observed are the correct description of high-multiplicity events and the flavour composition of final states. One striking observation, made recently by the ALICE collaboration, was that in highmultiplicity pp events properties similar to that of AA and pA collisions are observed [6].…”

Rope Hadronization and Strange Particle Production

“…Results are shown both for the original Dipsy implementation, as well as the Pythia8 implementation (the latter for pp only). The figure can be compared to experimental results obtained by ALICE [26]. Rope Hadronization can be seen to describe strangeness in all systems from e + e − to PbPb well.…”

Energy and multiplicity dependence of strange and non-strange particle production in proton-proton collisions at the LHC with ALICE

“…The yields of strange hadrons increase linearly with the charged particle multiplicity, and the production rate is the same at the two energies for a given multiplicity. It should also be noted that the yields of particles with larger strange quark content increase faster as a function of multiplicity as already reported in [5]. Data are compared to several Monte Carlo models.…”

“…Concerning the hadrochemistry one of the most intriguing results recently reported by the ALICE collaboration is the enhancement observed in the production of (multi-)strange hadrons relative to pions as a function of multiplicity in pp collisions at √ s = 7 TeV [5]. These are surprising observations, because strangeness enhancement was considered historically one of the signatures for the deconfinement in heavy-ion collisions [6], and also because none of the commonly-used pp Monte Carlo models reproduces quantitatively the existing data.…”