Event-shape studies of strangeness production in √S = 13 TeV proton–proton collisions with ALICE

Adrian Nassirpour,On Behalf Of The Alice Collaboration

doi:10.1051/epjconf/202225913005

Abstract

The ALICE Collaboration has observed that the relative fraction of strange hadrons grows strongly with multiplicity in small collision systems at LHC energies, in particular for multi-strange baryons. The origin of this effect is still under debate, and models need significant final-state interactions to accommodate the new ALICE results, requiring new tools to discriminate experimentally between the various phenomenological ideas. In these proceedings we present a multi-differential study of identified particle spectra with respect to the event multiplicity and two different event shape observables, the unweighted transverse spherocity SOpT=1, and the self-normalized, transverse charged particle density, RT, which allows us to explore particle production associated with hard and soft QCD processes. ALICE has measured π, K, ϕ, and Ξ production at mid-rapidity (|η| < 0.8) as a function of SOpT=1 and RT in pp collisions at √S = 13 TeV. This work reports on how these multi-differential measurements compare with predictions from PYTHIA and EPOSLHC.

Highlights

Measurements in proton–proton and proton–lead (p–Pb) collisions at the Large Hadron Collider (LHC) have revealed that the relative production of strange hadrons is enhanced in high-multiplicity events, and the strength of the enhancement increases with the strange quark content
Ξ-to-π ratios as a function of both EPOS-LHC and PYTHIA are able to qualitatively describe the double-ratios, which suggests that the simulations capture most of the
=1 selection but overestimate/underestimate the general enhancement of strange particle production in highmultiplicity events. Both the K/π and Ξ/π ratios highlight an overall relative enhancement of K and Ξ hadrons compared to pions in Isotropic events, and a suppression in Jetty events. This suggests that strangeness enhancement in high-multiplicity pp collisions is driven by the multiple softer collisions found in isotropic topologies, rather than hard processes

Summary

Introduction

Measurements in proton–proton (pp) and proton–lead (p–Pb) collisions at the Large Hadron Collider (LHC) have revealed that the relative production of strange hadrons is enhanced in high-multiplicity events, and the strength of the enhancement increases with the strange quark content. Multi-differential observables are needed in order to distinguish which of these models most accurately describes hadronization in high-multiplicity small-systems collisions; to understand whether the final-state multiplicity is the driving force for the enhancement of strange hadrons, or if both the multiplicity and strangeness enhancement are driven by underlying phenomena that are currently not well understood This contribution presents results from A Large Ion Collider Experiment (ALICE) on strange particle production as functions of the transverse spherocity, the self-normalized charged-particle density in the transverse region, RT, which relate to the event topology and the underlying event activity respectively. Π,K,p are identified via the specific energy loss dE/dx and the time-of-flight (TOF). φ and Ξ yields are extracted from invariant mass distributions of their identified decay daughters (φ → K+K− and Ξ−[Ξ+] → π−[π+] + Λ[Λ ])

Results

Particle production as a function of RT

Conclusion