Higher harmonic flow coefficients of identified hadrons in Pb-Pb collisions at s N N = 2.76 $$ \sqrt{s_{\mathrm{NN}}}=2.76 $$ TeV

Abstract

The elliptic, triangular, quadrangular and pentagonal anisotropic flow coefficients for π ± , K ± and p+p in Pb-Pb collisions at √ s NN = 2.76 TeV were measured with the ALICE detector at the Large Hadron Collider. The results were obtained with the Scalar Product method, correlating the identified hadrons with reference particles from a different pseudorapidity region. Effects not related to the common event symmetry planes (non-flow) were estimated using correlations in pp collisions and were subtracted from the measurement. The obtained flow coefficients exhibit a clear mass ordering for transverse momentum (p T ) values below ≈ 3 GeV/c. In the intermediate p T region (3 < p T < 6 GeV/c), particles group at an approximate level according to the number of constituent quarks, suggesting that coalescence might be the relevant particle production mechanism in this region. The results for p T < 3 GeV/c are described fairly well by a hydrodynamical model (iEBE-VISHNU) that uses initial conditions generated by A Multi-Phase Transport model (AMPT) and describes the expansion of the fireball using a value of 0.08 for the ratio of shear viscosity to entropy density (η/s), coupled to a hadronic cascade model (UrQMD). Finally, expectations from AMPT alone fail to quantitatively describe the measurements for all harmonics throughout the measured transverse momentum region. However, the comparison to the AMPT model highlights the importance of the late hadronic rescattering stage to the development of the observed mass ordering at low values of p T and of coalescence as a particle production mechanism for the particle type grouping at intermediate values of p T for all harmonics.

Systematic studies of correlations between different order flow harmonics in Pb-Pb collisions at sNN=2.76 TeV

“…The string melting configuration of the AMPT without hadronic rescattering was used to study the influence of the hadronic phase on the development of the anisotropic flow. Even though the string melting version of AMPT [78,99] observed in a recent study [100] that it fails to quantitatively reproduce the flow harmonics of identified hadrons (v 2 , v 3 , v 4 , and v 5 ) at √ s NN = 2.76 TeV. It turns out that the radial flow in AMPT is 25% lower than that measured at the LHC, which is responsible for this quantitative disagreement [100].…”

“…Even though the string melting version of AMPT [78,99] observed in a recent study [100] that it fails to quantitatively reproduce the flow harmonics of identified hadrons (v 2 , v 3 , v 4 , and v 5 ) at √ s NN = 2.76 TeV. It turns out that the radial flow in AMPT is 25% lower than that measured at the LHC, which is responsible for this quantitative disagreement [100]. The details of the AMPT configurations used in this article and the comparisons of p T -differential v n for pions, kaons, and protons to the data can be found in Ref.…”

“…The details of the AMPT configurations used in this article and the comparisons of p T -differential v n for pions, kaons, and protons to the data can be found in Ref. [100].…”

Heavy Ions Overview

“…Figure 1 shows results for the three main harmonic coefficients v 2 , v 3 , and v 4 as a function of transverse momentum p T for non-central Pb-Pb collisions at the LHC [3,4]. The most striking feature in the figures is the fact that the coefficients sharply increase with p T , and that the point at which this increase sets in depends on the mass of the particle.…”

“…The effects of jet quenching can be used to study the properties of the plasma. Figure 1: Amplitudes v n of the Fourier decomposition of the azimuthal distributions of particle production with respect to symmetry planes in the event, as a function of p T , for different particle species in 20 − 30% central Pb-Pb collisions at the LHC [3,4].…”