Identified-hadron pt spectra and collectivity in small systems

Not scheduled
20m
High Multiplicities (small system) High Multiplicities (small system)

Speaker

Thomas Trainor

Description

Certain data features that were attributed to quark-gluon plasma (QGP) formation in more-central A-A collisions -- evidence for radial flow and jet quenching in pt spectra, v2, v3, etc. in azimuth correlations, one or two "ridge" structures in long-range angular correlations -- have more recently been observed in high-multiplicity p-A and even p-p collisions. Arguing by analogy with A-A collisions it is suggested that a flowing dense medium or QGP may be formed even in small collision systems. Alternatively, one could argue that data features appearing in small low-density systems should not be associated with QGP, and alternative explanations are required for any collision system. In this talk I focus on evidence (or not) for radial flow and jet modification in pt spectra from several collision systems. I present a comparison of identified-hadron (PID) pt spectra from p-p, p-Pb, Au-Au and Pb-Pb collisions. The PID spectra are described with a two-component (soft + hard) model of hadron production. To the statistical limits of spectrum data radial flow is excluded from p-p and p-Pb spectra for any charge multiplicity, and is unlikely in A-A collisions as well. Jet modification is also excluded from p-p and p-Pb collisions, whereas strong modification is evident in more-central A-A collisions as has long been evident. The combined results suggest that QGP formation can be questioned for any collision system and that an alternative non-QGP explanation is required for v2 data.

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