The elliptic, $v_2$, triangular, $v_3$, and quadrangular, $v_4$, azimuthal anisotropic flow coefficients are measured for unidentified charged particles, pions and (anti-)protons in Pb-Pb collisions at $\snn = 2.76$ TeV with the ALICE detector at the Large Hadron Collider. Results obtained with the event plane and four-particle cumulant methods are reported for the pseudo-rapidity range $|\eta|< 0.8$ at different collision centralities and as a function of transverse momentum, $\pt$, out to $\pt=20$ GeV/$c$. The observed non-zero elliptic and triangular flow depends only weakly on transverse momentum for $\pt>8$ GeV/$c$. The small $\pt$ dependence of the difference between elliptic flow results obtained from the event plane and four-particle cumulant methods suggests a common origin of flow fluctuations up to $\pt=8$ GeV/$c$. The magnitude of the (anti-)proton elliptic and triangular flow is larger than that of pions out to at least $\pt=8$ GeV/$c$ indicating that the particle type dependence persists out to high $\pt$.
Phys. Lett. B 719 (2013) 18
HEP Data
e-Print: arXiv:1205.5761 | PDF | inSPIRE
CERN-PH-EP-2012-142
Figure 1
$v_2$, $v_3$, and $v_4$ measured for unidentified charged particles as a function of transverse momentum for various centrality classes. The dashed line represents the WHDG model calculations for neutral pions $v_2$ extrapolated to the LHC collision energy. For clarity, the markers for $v_3$ and $v_{4/\Psi_{2}}$ results are slightly shifted along the horizontal axis. Error bars (shaded boxes) represent the statistical (systematic) uncertainties. |  |
Figure 3
Relative event-by-event elliptic flow fluctuations for unidentified charged particles versus transverse momentum for different centrality classes. For clarity, the markers for centrality classes $\ge 10\%$ are slightly shifted along the horizontal axis. Error bars (shaded boxes) represent the statistical (systematic) uncertainties. |  |
Figure 4
Unidentified charged particle $v_2$, $v_3$, and $v_4$ integrated over the transverse momentum range $10< \pt< 20$ GeV/$c$ as a function of collision centrality, with the more central (peripheral) collisions shown on the left-(right-)hand side, respectively. The dashed line represents the WHDG model calculations for neutral pions extrapolated to the LHC collision energy. Error bars (shaded boxes) represent the statistical (systematic) uncertainties. |  |
Figure 5
$v_2$ (top) and $v_3$ (bottom) of charged pion and proton as a function of transverse momentum for 10-50% centrality class compared to unidentified charged particles results from the event plane method. For clarity, the markers for $v_2$ and $v_3$ at $\pt>8$ GeV/$c$ are slightly shifted along the horizontal axis. PHENIX $\pi^0$ $v_2$ measurements are also shown. The dashed line represents the WHDG model calculations for neutral pions extrapolated to the LHC collision energy for the 20-50% centrality range. Error bars (shaded boxes) represent the statistical (systematic) uncertainties. |  |