Impact parameter dependence of anisotropic flow: bayesian reconstruction in ultracentral nucleus-nucleus collisions
Peculiar phenomena have been observed in analyses of anisotropic flow (π£π) fluctuations in ultracentral nucleus-nucleus collisions: The fourth-order cumulant of the elliptic flow (π£2) distribution changes sign. In addition, the ATLAS Collaboration has shown that cumulants of π£π fluctuations of all o...
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| Main Authors: | , , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
9 December, 2024
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| In: |
Physical review
Year: 2024, Volume: 110, Issue: 6, Pages: 1-16 |
| ISSN: | 2469-9993 |
| DOI: | 10.1103/PhysRevC.110.064906 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1103/PhysRevC.110.064906 Verlag, lizenzpflichtig, Volltext: https://link.aps.org/doi/10.1103/PhysRevC.110.064906 
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| Author Notes: | Mubarak Alqahtani, Rajeev S. Bhalerao, Giuliano Giacalone, Andreas Kirchner, and Jean-Yves Ollitrault |
| Summary: | Peculiar phenomena have been observed in analyses of anisotropic flow (π£π) fluctuations in ultracentral nucleus-nucleus collisions: The fourth-order cumulant of the elliptic flow (π£2) distribution changes sign. In addition, the ATLAS Collaboration has shown that cumulants of π£π fluctuations of all orders depend significantly on the centrality estimator. We show that these peculiarities are due to the fact that the impact parameter π always spans a finite range for a fixed value of the centrality estimator. We provide a quantitative determination of this range through a simple Bayesian analysis. We obtain excellent fits of STAR and ATLAS data, with a few parameters, by assuming that the probability distribution of π£π solely depends on π at a given centrality. This probability distribution is almost Gaussian, and its parameters depend smoothly on π, in a way that is constrained by symmetry and scaling laws. We reconstruct, thus, the impact parameter dependence of the mean elliptic flow in the reaction plane in a model-independent manner, and assess the robustness of the extraction using Monte Carlo simulations of the collisions where the impact parameter is known. We argue that the non-Gaussianity of π£π fluctuations gives direct information on the hydrodynamic response to initial anisotropies, ATLAS data being consistent with a smaller response for π=4 than for π=2 and π=3, in agreement with hydrodynamic calculations. |
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| Item Description: | Gesehen am 06.05.2025 |
| Physical Description: | Online Resource |
| ISSN: | 2469-9993 |
| DOI: | 10.1103/PhysRevC.110.064906 |