Mean pt scaling with m/nq at the LHC: Absence of (hydro) flow in small systems?

Abstract

In this work, a study of the average transverse momentum (pt) as a function of the mid-rapidity charged hadron multiplicity (Nch) and hadron mass (m) in p-Pb and Pb-Pb collisions at LHC energies is presented. For the events producing low Nch, the average pt is found to scale with the reduced hadron mass, i.e., mass divided by the number of quark constituents (m/nq), this scaling also holds for inelastic pp collisions at RHIC and LHC energies. The scaling is broken in high multiplicity p-Pb and Pb-Pb collisions, where, for <Nch/deta> < 60 the average pt is higher for baryons than that for mesons, though they increase linearly with m/nq. This behavior is qualitatively well reproduced by Pythia 8, but not by hydro calculations, where an universal scaling with the hadron mass (and not with m/nq) is predicted for all the multiplicity event classes. Only the central (0-60%) Pb-Pb collisions behave as expected from hydro.

8 pages, 6 figures. Minor changes were implemented in the text

References in corpus (13)

• An Introduction to PYTHIA 8.2
• Tuning PYTHIA 8.1: the Monash 2013 Tune
• Observation of long-range near-side angular correlations in proton-lead collisions at the LHC
• String Formation Beyond Leading Colour
• The ridge in proton-proton collisions at the LHC
• Phobos results on charged particle multiplicity and pseudorapidity distributions in Au+Au, Cu+Cu, d+Au, and p+p collisions at ultra-relativistic energies
• K*(892)${}^0$ and $\Phi$(1020) production in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV
• Study of the inclusive production of charged pions, kaons, and protons in pp collisions at sqrt(s) = 0.9, 2.76, and 7 TeV
• Long-range azimuthal correlations in proton-proton and proton-nucleus collisions from the incoherent scattering of partons
• Mid-rapidity charged hadron transverse spherocity in pp collisions simulated with Pythia
• Thermal photon radiation in high multiplicity p+Pb collisions at the Large Hadron Collider
• Thoughts on opportunities from high-energy nuclear collisions
• Collectivity in high-multiplicity events of proton-proton collisions in the framework of String Percolation

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