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The hidden secrets of the event-shape fluctuations

The hidden secrets of the event-shape fluctuations. Jiangyong Jia. with Peng huo and Soumya Mohapatra arxiv:1311.7091, 1402.6680, 1403.6077. Geometry and harmonic flow. How (ε n ,Φ n * ) are transferred to (v n , Φ n )? What is the nature of final state (non-linear) dynamics?

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The hidden secrets of the event-shape fluctuations

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  1. The hidden secrets of the event-shape fluctuations Jiangyong Jia with Peng huo and Soumya Mohapatra arxiv:1311.7091, 1402.6680, 1403.6077

  2. Geometry and harmonic flow • How (εn,Φn*) are transferred to (vn, Φn)? • What is the nature of final state (non-linear) dynamics? • The nature of longitudinal flow dynamics?

  3. Event-by-event flow observables Many little-bang events JHEP11(2013)183 EbyE vn distribution:p(v2), p(v3), p(v4) Event-plane correlation: p(Φn,Φm) and p(Φn,Φm,ΦL) Soumya’s talk on Monday arXiv:1403.0489

  4. How (εn,Φn*) are transferred to (vn, Φn)? arXiv:1111.6538 • Flow response is linear for v2 and v3:

  5. How (εn,Φn*) are transferred to (vn, Φn)? arXiv:1111.6538 • Higher-order flow arises from EP correlations., e.g. : arXiv:1403.0489 • Flow response is linear for v2 and v3:

  6. Can we do better?

  7. Can we do better? Pb+Pb <ε2> • Variation of event shape at fixed centrality much bigger than Variation of mean across the full centrality range!! • All of this information has been averaged out!

  8. Can we do better? JHEP11(2013)183 • Variation of event shape at fixed centrality much bigger than Variation of mean across the full centrality range!! • All of this information has been averaged out!

  9. Hidden correlations in fixed-centrality Pb+Pb b=10fm • Correlation already exist in the initial state • e.g. anti-correlation between ε2 and ε3. • They are expected to influence the final state.

  10. Event-shape selection technique Schukraft, Timmins, and Voloshin, arXiv:1208.4563 Huo, Mohapatra, JJ arxiv:1311.7091 S Select events with certain v2,v3 p(vn)or p(Φn,Φm,…)

  11. AMPT model L Pang • AMPT model: Glauber+HIJING+transport • Has fluctuating geometry and collective flow • Longitudinal fluctuations and initial flow

  12. Event shape selection accuracy in AMPT -6<η<-2 b=8fm Events with certain v2,v3 Pb+Pb S • Fixed impact parameter b=8fm • Divide events into 10 equal bins • <ε2> vary by a factor of 3

  13. v2(η) : select on ε2 Flow suppressed v2(η)|η>0 when EP in -6<η<-2 v2(η)|η<0 when EP in 2<η<6 v2(η)||η|>2 when EP in |η|<1 Pb+Pb

  14. v2(η) : select on ε2 Flow suppressed v2(η)|η>0 when EP in -6<η<-2 v2(η)|η<0 when EP in 2<η<6 v2(η)||η|>2 when EP in |η|<1 Pb+Pb Flow enhanced Symmetric distribution expected

  15. v2(η) : compare with selection on q2 Suppression of flow in the selection window v2(η)|η>0 when EP in -6<η<-2 v2(η)|η<0 when EP in 2<η<6 v2(η)||η|>2 when EP in |η|<1 Pb+Pb enhancement of flow in the selection window

  16. What is the origin of v2(η) asymmetry? Pb+Pb Suppression/enhancement of flow in the selected window Decreasing response to flow selection outside the selection window

  17. Dependence of v3(η) on q2 in fixed centrality Pb+Pb v2 v3 v3 anti-correlated with v2 reflection of p(ε2,ε3)

  18. Two-Plane correlation selected on q2 Two types: ΦA2,ΦA4 ΦC2,ΦC4 Pb+Pb

  19. Two-Plane correlation selected on q2 Two types: ΦA2,ΦA4 ΦC2,ΦC4 Pb+Pb The full centrality dependence seen within one centrality bin!

  20. What is the origin of v2(η) asymmetry? Pb+Pb Suppression/enhancement of flow in the selected window Decreasing response to flow selection outside the selection window

  21. Longitudinal particle production wounded nucleon model Bialas, Bzdak, Zalewski, Wozniak…. STAR/PHOBOS Emission function of one wounded nucleon f(η) Extracted from d+Au data Phobos dAu Assumes that after the collision of two nuclei, the secondary particles are produced by independent fragmentation of wounded nucleons

  22. Forward/backward eccentricity fluctuations P.Huo, JJ 1403.6077 • Energy density profile in xy naturally interpolates between two limits • Fluctuations of participants in the two nuclei are not the same • So the forward event shape more correlated with and vice versa

  23. Consequence…… Backward Forward • Eccentricity vector interpolates between and • Equal to only at η=0 • Assuming hydro-response to be linear then (good for v2 and v3)

  24. FB eccentricity fluctuations from Glauber b=8fm Pb+Pb • Significant FB asymmetry: • Significant twist:

  25. What AMPT tell us? b=8fm Pb+Pb FB asymmetry survives

  26. What AMPT tell us? Pb+Pb b=8fm Initial twist survives • Twist in initial geometry appears as twist in the final state flow • Participant plane angles: • Final state event-plane angles

  27. How to measure the twist angle Backward Forward • Non-vanishing sine term if there is twist • Used to extract the twist angle in η. • Need event selection in order to see it.

  28. Select initial event-shape Select events with different asymmetry and twist at INITIAL STATE And then measure relative to the participant planes

  29. Type-1 Pb+Pb

  30. Type-2 Pb+Pb

  31. Type-3 Pb+Pb P.Huo, JJ 1402.6680, 1403.6077 Residual difference indicate other EP-decorrelation sources orthogonal to the event-shape selection

  32. Results for inclusive events Pb+Pb Results depend on which PP used, clearly suggest the influence of decorrelation effects.

  33. Implications Pb+Pb • System not boost-invariant EbyEnot only for dN/dη, but also flow • Longitudinal decorrelation effects breaks the factorization, despite being initial state effects. • Decorrelation effects much stronger in p+A and Cu+Au system

  34. Summary Event-shape selection and event twist techniques • Event-shape fluctuations are much richer than what is currently studied • Strong fluctuation/correlation between vnand Φns within given centrality • Rich patterns forward/backward EbyE flow fluctuations: • These initial state fluctuations are very large (comparable to the entire centrality dependence) and they are expected to survive collective expansion. We demonstrated this via the AMPT model • New avenue to study initial state fluctuations, particle production and collective expansion dynamics • More detailed study via EbyEhydro are needed.

  35. Backup

  36. p(vn) distributions JHEP11(2013)183 Probability distributions for v2, v3 and v4 in many centrality ranges

  37. Event-plane correlations arXiv:1403.0489 Two-plane Three-plane Event-plane correlators with rich centrality dependence

  38. Rapidity fluctuations of flow X.N. Wang. • vn(η) for events selected on εn or qn show direct evidence for decorrelation. Au+Au collision @ 200 GeV : Ideal hydrodynamics • Previous study suggest EP correlation weakens with larger η gap in AMPT

  39. vn(η) shape for all n: select on q2 v2 v3 v4 v5 v6 Anti-correlation with v3  reflection of p(ε2,ε3) v4, v5, v6 correlates with v2 selection, direct measure of non-linear effects!!

  40. Type-4 • But cross point is pushed to backward rapidity. Similar to Type-3

  41. Compare to Event Plane result 41 Type-1 Type-2

  42. Compare to Event Plane result Type-3 Type-4

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