Non-linear flow modes of identified particles in Pb-Pb collisions at s NN $$ \sqrt{s_{\mathrm{NN}}} $$ = 5 . 02 TeV
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Springer
Received: February 10, Revised: May 11, Accepted: June 7, Published: June 24,
2020 2020 2020 2020
The ALICE collaboration E-mail: [email protected] Abstract: The pT -differential non-linear flow modes, v4,22 , v5,32 , v6,33 and v6,222 for π ± , √ K± , K0S , p + p, Λ + Λ and φ-meson have been measured for the first time at sNN = 5.02 TeV in Pb-Pb collisions with the ALICE detector at the Large Hadron Collider. The results were obtained with a multi-particle technique, correlating the identified hadrons with reference charged particles from a different pseudorapidity region. These non-linear observables probe the contribution from the second and third order initial spatial anisotropy coefficients to higher flow harmonics. All the characteristic features observed in previous pT -differential anisotropic flow measurements for various particle species are also present in the non-linear flow modes, i.e. increase of magnitude with increasing centrality percentile, mass ordering at low pT and particle type grouping in the intermediate pT range. Hydrodynamical calculations (iEBE-VISHNU) that use different initial conditions and values of shear and bulk viscosity to entropy density ratios are confronted with the data at low transverse momenta. These calculations exhibit a better agreement with the anisotropic flow coefficients than the non-linear flow modes. These observations indicate that non-linear flow modes can provide additional discriminatory power in the study of initial conditions as well as new stringent constraints to hydrodynamical calculations. Keywords: Heavy Ion Experiments ArXiv ePrint: 1912.00740
Open Access, Copyright CERN, for the benefit of the ALICE Collaboration. Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP06(2020)147
JHEP06(2020)147
Non-linear flow modes of identified particles in Pb-Pb √ collisions at sNN = 5.02 TeV
Contents 1
2 Experimental setup
4
3 Event sample, track selection and particle identification 3.1 Trigger selection and data sample 3.2 Selection of primary π ± , K± and p + p 3.3 Reconstruction of K0S , Λ + Λ and φ meson
5 5 6 7
4 Analysis method
8
5 Systematic uncertainties
9
6 Results and discussion 6.1 Centrality and pT dependence of non-linear flow modes 6.2 Comparison with vn of identified particles 6.3 Comparison with models
11 12 17 18
7 Summary
25
A Additional figures A.1 KET scaling
31 31
The ALICE collaboration
41
1
Introduction
Lattice quantum chromodynamics (QCD) calculations [1, 2] suggest that at extremely high temperature and energy density a state of matter is produced in which quarks and gluons are no longer confined into hadrons. This state of matter is called the quark-gluon plasma (QGP) [3–5]. The main goal of heavy-ion collision experiments is to study the properties of the QGP, such as the speed of sound, the equation of state and its shear and bulk viscosities. One of the observables sensitive to these properties is the azimuthal angular distribution of particles emitted in the plane perpendicular to the beam
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