Abstract
The multiplicity dependence of the pseudorapidity density of charged particles in proton–proton (pp) collisions at centre-of-mass energies sqrt{s}~=~5.02, 7 and 13 TeV measured by ALICE is reported. The analysis relies on track segments measured in the midrapidity range (|eta | < 1.5). Results are presented for inelastic events having at least one charged particle produced in the pseudorapidity interval |eta |<1. The multiplicity dependence of the pseudorapidity density of charged particles is measured with mid- and forward rapidity multiplicity estimators, the latter being less affected by autocorrelations. A detailed comparison with predictions from the PYTHIA 8 and EPOS LHC event generators is also presented. The results can be used to constrain models for particle production as a function of multiplicity in pp collisions.
Highlights
The study of high-multiplicity events in proton–proton and proton–nucleus high-energy collisions reveals striking similarities with respect to the observations made for larger systems like a nucleus–nucleus collision, which are interpreted in terms of the creation of a strongly-interacting, fluid-like QCD medium: the quark–gluon plasma (QGP)
In pp and p–Pb collisions, the selection of events with large hadronic final-state multiplicities biases the sample towards a large average number of Multiple Parton Interactions (MPIs) at the LHC [9,10]
In the description provided by the colour reconnection (CR) mechanism [11,12], CR in MPIs is expected to be pronounced at high multiplicity
Summary
The study of high-multiplicity events in proton–proton (pp) and proton–nucleus high-energy collisions reveals striking similarities with respect to the observations made for larger systems like a nucleus–nucleus collision, which are interpreted in terms of the creation of a strongly-interacting, fluid-like QCD medium: the quark–gluon plasma (QGP). An ALICE measurement reported an enhancement in the relative production of (multi) strange particles with respect to primary charged particles as a function of multiplicity in pp collisions [8]. This suggests that some observables related to the QGP formation might be driven just by the multiplicity regardless of collision systems at LHC energies. This document provides a large set of charged-particle multiplicity density measurements as a function of event multiplicity in pp collisions at different centre-of-mass energies. Measurements are performed for inelastic collisions with at least one charged particle produced in |η| < 1 (INEL>0), corresponding to about 75% of the total inelastic cross section [13,23,25,26]
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