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| CMS-PAS-HIN-18-001 | ||
| Charged particle angular correlations in XeXe collision at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.44 TeV | ||
| CMS Collaboration | ||
| May 2018 | ||
| Abstract: Azimuthal correlations of charged particles in xenon-xenon collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.44 TeV are studied using data collected by the CMS experiment at the CERN LHC. The $v_{2}$, $v_{3}$, and $v_{4}$ Fourier coefficients that characterize the azimuthal behavior are obtained using two-particle correlations, the scalar product method and the multiparticle cumulant method. Within a hydrodynamic picture, these methods have different sensitivities to non-flow and flow fluctuation effects. The system size dependence of the results is explored by taking ratios with comparable results found in PbPb collisions. Model calculations that include fluctuation effects are compared to the experimental results. | ||
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Links:
CDS record (PDF) ;
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These preliminary results are superseded in this paper, PRC 100 (2019) 044902. The superseded preliminary plots can be found here. |
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| Figures | Summary | Additional Figures | References | CMS Publications |
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| Figures | |
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Figure 1:
Elliptic flow coefficient, $v_2$, based on different analysis techniques, as a function of transverse momentum and in eleven centrality bins. The results for the 2- and multi-particle correlations correspond to the range $|\eta | < $ 2.4, while the SP results are for $|\eta | < $ 0.8. The shaded boxes represent systematic uncertainties. |
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Figure 2:
Triangular flow coefficients, $v_3$, based on the different analysis techniques, as a function of transverse momentum and in eleven centrality bins. The results for the 2- and multi-particle correlations correspond to the range $|\eta | < $ 2.4, while the SP results are for $|\eta | < $ 0.8. The shaded boxes represent systematic uncertainties. |
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Figure 3:
The $v_4$ coefficients, based on the different analysis techniques, as a function of transverse momentum and in eleven centrality bins. The results for the 2- and multi-particle correlations correspond to the range $|\eta | < $ 2.4, while the SP results are for $|\eta | < $ 0.8. The shaded boxes represent systematic uncertainties. |
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Figure 4:
Centrality dependence of the spectrum-weighted $v_2$, $v_3$ and $v_4$ flow harmonics with 0.3 $ < p_{\mathrm{T}} < $ 3.0 GeV/$c$. The $v_2$ results are shown for 2-, 4-, 6- and 8-particle correlations (left panel). The $v_3$ results are shown for 2- and 4-particle correlations (middle panel), while the $v_4$ values are presented for two-particle correlations technique, only. The shaded boxes represent systematic uncertainties. |
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Figure 5:
Centrality dependence of $v_2\{4\}/v_2\{2\}$, $v_2\{6\}/v_2\{4\}$ (left panel) and $v_3\{4\}/v_3\{2\}$ (right panel) ratios. Theoretical predictions based on the IP-Glasma + Music + UrQMD and the hydrodynamic model from Ref. [31] are compared to the data. |
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Figure 6:
Comparison of $v_2$ results measured with two-particle correlations from two different systems, XeXe collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.44 TeV and PbPb collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV, shown as a function of $ p_{\mathrm{T}} $ in eleven centrality bins. The shaded boxes represent systematic uncertainties. |
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Figure 7:
Comparison of $v_3$ results measured with two-particle correlations from two different systems, XeXe collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.44 TeV and PbPb collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV shown as a function of $ p_{\mathrm{T}} $ in eleven centrality bins. The shaded boxes represent systematic uncertainties. |
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Figure 8:
Comparison of $v_4$ results measured with two-particle correlations from two different systems, XeXe collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.44 TeV and PbPb collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV, shown as a function of $ p_{\mathrm{T}} $ in eleven centrality bins. The shaded boxes represent systematic uncertainties. |
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Figure 9:
Centrality dependence of the spectrum-weighted $v_2$, $v_3$, and $v_4$ harmonic coefficient from two-particle correlations method with 0.3 $ < p_{\mathrm{T}} < $ 3.0 GeV/$c$ for XeXe collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.44 TeV and PbPb collisions at $ {\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV. The lower panels show the ratio of the results for the two systems. Theoretical predictions from Ref. [31] are compared to the data. The shaded boxes represent systematic uncertainties. |
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Figure 10:
Ratio of the $v_2$, $v_3$, and $v_4$ harmonic coefficients from two-particle correlations for XeXe and PbPb collisions as a function of $ p_{\mathrm{T}} $ in eleven centrality bins. The shaded boxes represent systematic uncertainties. |
| Summary |
| In this note, the $v_2,v_3$ and $v_4$ azimuthal flow harmonics are shown for XeXe collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.44 based on data obtained using the CMS detector. Three different analysis techniques, including two-particle correlations, the scalar product method, and the multiparticle cumulant method, are used to explore the fluctuation behavior through the different effect of flow fluctuations on each of these techniques. The harmonic coefficients are compared to those found with PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV to explore the influence of the system size. The magnitude of the $v_2$ coefficients for XeXe collisions are larger than found in PbPb collisions for the most central collisions. This is attributed to a larger fluctuation component in the lighter collision system. In more peripheral events, PbPb $v_n$ coefficients are consistently greater than those found for XeXe collisions. This behavior is qualitatively consistent with expectations from hydrodynamic models. A clear ordering $v_2\{2\} > v_2\{4\} \approx v_2\{6\} \approx v_2\{8\}$ is observed, with a splitting of 2-3% for $v_2\{6\}/v_2\{4\}$. The $v_3\{4\} / v_3\{2\}$ ratio is found to be significantly smaller than the $v_2\{4\} / v_2\{2\}$ ratio for XeXe collisions, suggesting a dominant fluctuation component for the $v_3$ harmonic. Hydrodynamic models that consider the xenon nuclear deformation are better able to reproduce the centrality dependence of the $v_{2}[\mathrm{XeXe}]/v_{2}[\mathrm{PbPb}]$ ratio, although the deformation appears to have little effect on the overall fluctuation behavior. These measurements provide new tests on the hydrodynamics models and help to constrain hydrodynamical descriptions of the nuclear collisions. |
| Additional Figures | |
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Additional Figure 1:
Upper panel: $v_2$ measured with two-particle correlations as a function of centrality in XeXe collisions from HYDJET generator at 5.44 TeV after selecting events based on the generator level $N_{\text{coll}}$ (circles), or using event selection based on total $E_{\mathrm{T}}$ measured in forward region (squares). Bottom panel: the ratio of the blue to the red points in the upper panel. |
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Additional Figure 2:
Upper panel: $v_2$ measured with multi-particle cumulants as a function of centrality in XeXe collisions from HYDJET generator at 5.44 TeV after selecting events based on the generator level $N_{\text{coll}}$ (circles), or using event selection based on total $E_{\mathrm{T}}$ measured in forward region (squares). Bottom panel: the ratio of the blue to the red points in the upper panel. |
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Additional Figure 3:
Upper panel: $v_3$ measured with two-particle correlations as a function of centrality in XeXe collisions from HYDJET generator at 5.44 TeV after selecting events based on the generator level $N_{\text{coll}}$ (circles), or using event selection based on total $E_{\mathrm{T}}$ measured in forward region (squares). Bottom panel: the ratio of the blue to the red points in the upper panel. |
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