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| CMS-PAS-HIN-23-002 | ||
| Elliptic anisotropy at high $ p_{\mathrm{T}} $ in pPb collisions using subevent cumulants | ||
| CMS Collaboration | ||
| 12 June 2024 | ||
| Abstract: The second-order (elliptic) Fourier coefficients ($ v_{2} $) as a function of particle transverse momentum ($ p_\mathrm{T} $) and event multiplicity are presented for pPb collisions using a subevent multiparticle cumulant analysis where nonflow effects are strongly suppressed. The data were recorded by the CMS experiment at a nucleon-nucleon center-of-mass energy of $ \sqrt{s_{_{\mathrm{NN}}}} = $ 8.16 TeV. The new measurement probes an extended range of particle $ p_\mathrm{T} $, up to values where the influence of nonflow effects are shown to strongly influence the results using a standard cumulant analysis. Results for both pPb and PbPb collisions are compared in similar multiplicity ranges, allowing for an assessment of the medium influence on the elliptic anisotropy associated with high $ p_\mathrm{T} $ particle production. | ||
| Links: CDS record (PDF) ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Subevent chosen in various cases in the CMS tracker acceptance to correlate four particles |
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Figure 2:
$ v_{2}\{4\} $ vs $ p_T $ in 185 $ \leq \mathrm{N}^{\mathrm{offline}}_{\mathrm{trk}} < $ 250 for pPb (Left) and PbPb (Right). Statistical uncertainty is represented by solid lines and systematic uncertainty by boxes. |
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Figure 3:
Left: Comparison of $ v_{2}\{4\} $ with 4 subevent vs $ p_T $ in 185 $ \leq \mathrm{N}^{\mathrm{offline}}_{\mathrm{trk}} < $ 250 between pPb and PbPb. Right: Comparison of $ v_{2}\{4\} $ with 4 subevent vs $ \langle \mathrm{N}^{\mathrm{offline}}_{\mathrm{trk}}\rangle $ for $ p_{\mathrm{T}} $ of POI $ > $ 6 GeV between pPb and PbPb. Statistical uncertainty is represented by solid lines and systematic uncertainty by boxes. |
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Figure 3-a:
Left: Comparison of $ v_{2}\{4\} $ with 4 subevent vs $ p_T $ in 185 $ \leq \mathrm{N}^{\mathrm{offline}}_{\mathrm{trk}} < $ 250 between pPb and PbPb. Right: Comparison of $ v_{2}\{4\} $ with 4 subevent vs $ \langle \mathrm{N}^{\mathrm{offline}}_{\mathrm{trk}}\rangle $ for $ p_{\mathrm{T}} $ of POI $ > $ 6 GeV between pPb and PbPb. Statistical uncertainty is represented by solid lines and systematic uncertainty by boxes. |
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Figure 3-b:
Left: Comparison of $ v_{2}\{4\} $ with 4 subevent vs $ p_T $ in 185 $ \leq \mathrm{N}^{\mathrm{offline}}_{\mathrm{trk}} < $ 250 between pPb and PbPb. Right: Comparison of $ v_{2}\{4\} $ with 4 subevent vs $ \langle \mathrm{N}^{\mathrm{offline}}_{\mathrm{trk}}\rangle $ for $ p_{\mathrm{T}} $ of POI $ > $ 6 GeV between pPb and PbPb. Statistical uncertainty is represented by solid lines and systematic uncertainty by boxes. |
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Figure 4:
Comparison of $ v_{2}\{4\} $ values with $ p_{\mathrm{T}}^{\mathrm{POI}} > $ 6 GeV based on the 4-subevent method as a function of $ \langle \mathrm{N}^{\mathrm{corrected}}_{\mathrm{trk}} \rangle $ between pPb and PbPb. The solid lines and boxes indicate the statistical and systematic uncertainties, respectively. |
| Tables | |
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Table 1:
Average multiplicity $ \langle \mathrm{N}^{\mathrm{offline}}_{\mathrm{trk}}\rangle $ and tracking efficiency corrected multiplicity $ \langle \mathrm{N}^{\mathrm{corrected}}_{\mathrm{trk}} \rangle $ in various $ \mathrm{N}^{\mathrm{offline}}_{\mathrm{trk}} $ bin is given below. |
| Summary |
| In summary, the $ v_{2}\{4\} $ values calculated using subevents are presented for pPb and PbPb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 8.16 TeV and $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 5.02 TeV, respectively. This analysis investigates an extended phase space region that has not been previously studied in small systems. After using a subevent method to remove nonflow correlations due to jet fragmentation, a significant and positive value for $ v_n\{4\} $ is determined for higher multiplicity pPb events extending to high particle $ p_\mathrm{T} $. A striking similarity is observed in the magnitudes of high $ p_{\mathrm{T}} v_{2}\{4\} $ values in high multiplicity pPb and peripheral PbPb collisions, suggesting a similar mechanism for the observed anisotropy at high $ p_{\mathrm{T}} $ in the two systems. These results provide new information on the interaction of high-$ p_{\mathrm{T}} $ partons with the surrounding medium in heavy ion collisions. |
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