Harmonic decomposition of two-particle angular correlations in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV

ALICE Collaboration

doi:10.1016/j.physletb.2012.01.060

paper

Harmonic decomposition of two-particle angular correlations in Pb-Pb collisions at $s_{NN}$ = 2.76 TeV

arXiv:1109.2501 · doi:10.1016/j.physletb.2012.01.060

Abstract

Angular correlations between unidentified charged trigger ( $t$ ) and associated ( $a$ ) particles are measured by the ALICE experiment in Pb-Pb collisions at $s_{NN} = 2.76$ TeV for transverse momenta $0.25 < p_{T}^{t, a} < 15$ GeV/ $c$ , where $p_{T}^{t} > p_{T}^{a}$ . The shapes of the pair correlation distributions are studied in a variety of collision centrality classes between 0 and 50% of the total hadronic cross section for particles in the pseudorapidity interval $∣ η ∣ < 1.0$ . Distributions in relative azimuth $Δ ϕ \equiv ϕ^{t} - ϕ^{a}$ are analyzed for $∣Δ η ∣ \equiv ∣ η^{t} - η^{a} ∣ > 0.8$ , and are referred to as "long-range correlations". Fourier components $V_{n Δ} \equiv ⟨ cos (n Δ ϕ)⟩$ are extracted from the long-range azimuthal correlation functions. If particle pairs are correlated to one another through their individual correlation to a common symmetry plane, then the pair anisotropy $V_{n Δ} (p_{T}^{t}, p_{T}^{a})$ is fully described in terms of single-particle anisotropies $v_{n} (p_{T})$ as $V_{n Δ} (p_{T}^{t}, p_{T}^{a}) = v_{n} (p_{T}^{t}) v_{n} (p_{T}^{a})$ . This expectation is tested for $1 \leq n \leq 5$ by applying a global fit of all $V_{n Δ} (p_{T}^{t}, p_{T}^{a})$ to obtain the best values $v_{n} {GF} (p_{T})$ . It is found that for $2 \leq n \leq 5$ , the fit agrees well with data up to $p_{T}^{a} \sim 3$ -4 GeV/ $c$ , with a trend of increasing deviation as $p_{T}^{t}$ and $p_{T}^{a}$ are increased or as collisions become more peripheral. This suggests that no pair correlation harmonic can be described over the full $0.25 < p_{T} < 15$ GeV/ $c$ range using a single $v_{n} (p_{T})$ curve; such a description is however approximately possible for $2 \leq n \leq 5$ when $p_{T}^{a} < 4$ GeV/ $c$ . For the $n = 1$ harmonic, however, a single $v_{1} (p_{T}$ curve is not obtained even within the reduced range $p_{T}^{a} < 4$ GeV/ $c$ .

26 pages, 11 captioned figures, 2 tables, authors from page 20, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/3504

Harmonic decomposition of two-particle angular correlations in Pb-Pb collisions at $s_{NN}$ = 2.76 TeV

Abstract

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Harmonic decomposition of two-particle angular correlations in Pb-Pb collisions at sNN​​ = 2.76 TeV

Abstract

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Cited by in corpus (169)

Harmonic decomposition of two-particle angular correlations in Pb-Pb collisions at $s_{NN}$ = 2.76 TeV