“School of Particles And Accelerator”

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Paper   IPM / Particles And Accelerator / 15752
School of Particles and Accelerator
  Title:   Non-Bessel-Gaussianity and Flow Harmonic Fine-Splitting
1.  Hadi Mehrabpour
2.  Seyed Farid Taghavi
  Status:   Published
  Journal: Eur. Phys. J. C
  No.:  1, 88
  Vol.:  79
  Year:  2019
  Supported by:  IPM
Both collision geometry and event-by-event fluctuations are encoded in the experimentally observed flow harmonic distribution p(vn) and 2k-particle cumulants cn{2k}. In the present study, we systematically connect these observables to each other by employing Gram-Charlier A series. We quantify the deviation of p(vn) from Bessel-Gaussianity in terms of flow harmonic fine-splitting. Subsequently, we show that the corrected Bessel-Gaussian distribution can fit the simulated data better than the Bessel-Gaussian distribution in the more peripheral collisions. Inspired by Gram-Charlier A series, we introduce a new set of cumulants qn{2k} that are more natural to study distributions near Bessel-Gaussian. These new cumulants are obtained from cn{2k} where the collision geometry effect is extracted from it. By exploiting q2{2k}, we introduce a new set of estimators for averaged ellipticity \vb2 which are more accurate compared to v2{2k} for k > 1. As another application of q2{2k}, we show we are able to restrict the phase space of v2{4}, v2{6} and v2{8} by demanding the consistency of \vb2 and v2{2k} with q2{2k} equation. The allowed phase space is a region such that v2{4}−v2{6} >~0 and 12 v2{6}−11v2{8}−v2{4} >~0, which is compatible with the experimental observations.

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