Centrality dependence of dihadron correlations and azimuthal anisotropy harmonics in PbPb collisions at $\sqrt{s_{NN}}= 2.76\ \mbox{TeV}$

Abstract

Measurements from the CMS experiment at the LHC of dihadron correlations for charged particles produced in PbPb collisions at a nucleon-nucleon centre-of-mass energy of 2.76 TeV are presented. The results are reported as a function of the particle transverse momenta (p T ) and collision centrality over a broad range in relative pseudorapidity ( η) and the full range of relative azimuthal angle ( φ). The observed two-dimensional correlation structure in η and φ is characterised by a narrow peak at ( η, φ) ≈ (0, 0) from jet-like correlations and a longrange structure that persists up to at least | η| = 4. An enhancement of the magnitude of the short-range jet peak is observed with increasing centrality, especially for particles of p T around 1-2 GeV/c. The long-range azimuthal dihadron correlations are extensively studied using a Fourier decomposition analysis. The extracted Fourier coefficients are found to factorise into a product of single-particle azimuthal anisotropies up to p T ≈ 3-3.5 GeV/c for at least one particle from each pair, except for the second-order harmonics in the most central PbPb events. Various orders of the single-particle azimuthal anisotropy harmonics are extracted for associated particle p

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

“…Recent anisotropic flow measurements for charged particles at the LHC [15][16][17][18][19][20][21][22] indicate that the system created in Pb-Pb collisions at √ s NN = 2.76 TeV also behaves as a strongly interacting liquid. An additional constraint on the value of η/s can be obtained by studying the flow coefficients of eq.…”

“…The existence of the QGP has been stipulated by observations at the Relativistic Heavy Ion Collider (RHIC) [7][8][9][10]. The first experimental results from the heavy-ion program at the LHC [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] have also provided evidence of the existence of the QGP in this new energy regime.-1 - …”

Multiparticle azimuthal correlations inp-Pb and Pb-Pb collisions at the CERN Large Hadron Collider

“…While the initial state anisotropy is usually dominated by an elliptical overlap area which gives rise to v 2 , measurements of the third harmonic flow (v 3 , triangular flow) demonstrated initial state fluctuations modulate the overlap area, and they provide additional constraints to the transport coefficients of the system (e.g., the value of the shear viscosity over entropy ratio η/s) [7][8][9][10][11]. The combination of the second and higher harmonic flow coefficients manifest themselves in two-particle correlation structures (along η) such as the away-side double hump ( ϕ ∼ π ), and near-side ridge ( ϕ ∼ 0) observed both at RHIC and the LHC.…”

Characterization of initial fluctuations for the hydrodynamical description of heavy ion collisions

“…In recent years, data from ultrarelativistic nucleus-nucleus collisions at the CERN Large Hadron Collider [1][2][3][4] and at BNL Relativistic Heavy Ion Collider [5][6][7] have been understood as giving strong support to a dynamical picture according to which the produced soft hadronic distributions in transverse momentum, azimuthal orientation, centrality, and particle species are determined by the fluid dynamic response to fluctuating initial conditions [8][9][10][11][12]. A detailed dynamical exploration of this picture has the potential of addressing central questions in the study of hot and dense QCD matter with nucleus-nucleus collisions.…”