Importance of correlations and fluctuations on the initial source eccentricity in high-energy nucleus-nucleus collisions

By Burak Han Alver, B. Back, M. Baker, M. Ballintijn, D. Barton, R. Betts, R. Bindel, W. Busza, V. Chetluru, E. Garcia and 29 more. 2007

243 citations recorded by the source corpus.

In relativistic heavy-ion collisions, anisotropic collective flow is driven, event by event, by the initial eccentricity of the matter created in the nuclear overlap zone. Interpretation of the anisotropic flow data thus requires a detailed understanding of the effective initial source eccentricity of the event sample. In this paper, we investigate various ways of defining this effective eccentricity using the Monte Carlo Glauber (MCG) approach. In particular, we examine the participant eccentricity, which quantifies the eccentricity of the initial source shape by the major axes of the ellipse formed by the interaction points of the participating nucleons. We show that reasonable variation of the density parameters in the Glauber calculation, as well as variations in how matter production is modeled, do not significantly modify the already established behavior of the participant eccentricity as a function of collision centrality. Focusing on event-by-event fluctuations and correlations of the distributions of participating nucleons, we demonstrate that, depending on the achieved event-plane resolution, fluctuations in the elliptic flow magnitude v{sub 2} lead to most measurements being sensitive to the root-mean-square rather than the mean of the v{sub 2} distribution. Neglecting correlations among participants, we derive analytical expressions for the participant eccentricity cumulants as amore » function of the number of participating nucleons, N{sub part}, keeping nonnegligible contributions up to O(1/N{sub part}{sup 3}). We find that the derived expressions yield the same results as obtained from mixed-event MCG calculations which remove the correlations stemming from the nuclear collision process. Most importantly, we conclude from the comparison with MCG calculations that the fourth-order participant eccentricity cumulant does not approach the spatial anisotropy obtained assuming a smooth nuclear matter distribution. In particular, for the Cu+Cu system, these quantities deviate from each other by almost a factor of 2 over a wide range in centrality. This deviation reflects the essential role of participant spatial correlations in the interaction of two nuclei.« less

Subfields: Aerospace Engineering, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/98aef82ff7643a67ad4490c6515fc8f7b7fcd344

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Citations in the corpus

Study of high-pT charged particle suppression in PbPb compared to pp collisions at sqrt(sNN)=2.76 TeV (2012, methodology): “This factor is computed as the ratio between the number of binary nucleon-nucleon collisions Ncoll, calculated from the Glauber model of the nuclear collision geometry [10], and the inelastic nucleon-nucleon (NN) cross section σNN inel = 64± 5 mb at √ s = 2.”
Study of high-pT charged particle suppression in PbPb compared to pp collisions at $\sqrt{s_{\mathrm{NN}}}=2.76~\mathrm{TeV}$ (2012, methodology): “This factor is computed as the ratio between the number of binary nucleon–nucleon collisions Ncoll, calculated from the Glauber model of the nuclear collision geometry [10], and the inelastic nucleon– nucleon (NN) cross section σ NN inel = 64 ± 5 mb at √ s = 2.”
Properties of hot and dense matter from relativistic heavy ion collisions (2015, background): “More recently, it was realized that fluctuations in the initial energy density generate substantial higher harmonics, including odd Fourier moments such as v3 [184], as well as fluctuations of the flow angles relative to the impact parameter plane [185].”
Relativistic Fluid Dynamics in and out of Equilibrium (2017, background): “[346] can then be obtained as [341, 347] v{abs} n (p⊥, Y ) = 1 events ∑”
Charged-particle nuclear modification factors in PbPb and pPb collisions at √(s_N N) = 5.02 TeV (2017, methodology): “The calculation of these properties is based on a Glauber model of the incoming nuclei [12, 17] and studies of bin-to-bin smearing, which is evaluated by examining the effects of finite resolution on fully simulated and reconstructed events [18].”
Improved Monte Carlo Glauber predictions at present and future nuclear colliders (2017, methodology): “Historically, either π [23] or 4π [24] have been used, where the latter essentially coincides with the geometrical overlap area of two uniform disks.”