Multiplicity dependence study of the pseudorapidity density distribution of charged particles in pp collisions with ALICE

Reported in this contribution, is the multiplicity dependence of the pseudorapidity density distribution of charged particles in proton-proton (pp) collisions at √s = 5.02 TeV and at 13 TeV with the ALICE experiment. The measurements rely on track segments reconstructed with the Silicon Pixel Detector in the kinematic region ∣η∣ < 1.8. Results are presented for three different event classes: inelastic (INEL), inelastic events with at least one charged particle in the central region ∣η∣ < 1.0 (INEL > 0), and non-single-diffractive (NSD) events for pp collisions at √s = 5.02 TeV. The measurements are shown for different multiplicity slices, defined by a forward multiplicity estimator and a central multiplicity estimator, which manifest different physics. To understand better the role of collective effects that have been recently observed in pp collisions, the evolution of the shapes of pseudorapidity density distributions at very high multiplicities is presented for pp collisions at √s = 13 TeV using data collected with high-multiplicity triggers. The results are compared to the predictions from the QCD-inspired Monte Carlo (MC) event generator PYTHIA and to expectations from the hydrodynamically treated MC event generator EPOS-LHC. (author)