Abstract
The journal Nature recently published a letter titled "Creating small circular, elliptical, and triangular droplets of quark-gluon plasma" [1]. The basis for that claim is a combination of measured Fourier amplitudes v2 and v3 from collision systems p-Au, d-Au and h-Au (helion h is the nucleus of atom 3He), Glauber Monte Carlo estimates of initial-state transverse collision geometries for those systems and hydrodynamic Monte Carlo descriptions of the vn data. Apparent correspondence between hydrodynamic model vn trends and data trends is interpreted as confirmation of “collectivity” occurring in the small collision systems, further interpreted to indicate QGP formation. QGP formation in small systems runs counter to pre-RHIC theoretical assumptions that QGP formation should require large collision systems (e.g. central A-A collisions). There is currently available a broad context of experimental data from p-p, A-A and p-Pb collisions at the RHIC and LHC against which the validity of the Nature letter claims may be evaluated. This talk provides a summary of such results and their implications. [1] Nature Phys. 15, no. 3, 214 (2019).
Highlights
A recent letter published in the journal Nature reports observation of “short-lived QGP droplets” in 200 GeV p-Au, d-Au and h-Au (h representing the helion nucleus of 3He) [1]
The overall argument is based on five critical assumptions that have been challenged in Ref. [2]
Fourier amplitudes vn inferred from two-particle angular correlations can be derived from direct model fits to full 2D angular correlations or from Fourier fits to 1D azimuth projections of 2D angular correlations
Summary
A recent letter published in the journal Nature reports observation of “short-lived QGP droplets” in 200 GeV p-Au, d-Au and h-Au (h representing the helion nucleus of 3He) [1]. The claimed observation is based on a combination of Glauber Monte Carlo estimates of initial conditions (IC), hydrodynamic theory evolution from the IC to the hadronic final state and comparison of theory results with measurements of azimuth Fourier components v2(pt) and v3(pt). The letter concludes: “...hydrodynamical models which include QGP formation provide a simultaneous and quantitative description of the data in three systems.”. The context for comparison is the two-component (soft + hard) model (TCM) of hadron production in high-energy nuclear collisions. Arguments in favor are based on azimuthal asymmetries (v2, v3 etc.) and jet quenching (RAA high-pt suppression) as common manifestations of a dense and flowing QCD medium or QGP. That assumption can be strongly questioned based on analysis of ensemble-mean pt data from 5 TeV p-Pb collisions
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