1 / 40

Event by Event Fluctuations

Topics in Heavy Ion Collisions, Montreal 2003. Event by Event Fluctuations. P t Fluctuations Balance Function Net Charge Fluctuations Conclusions. Claude A Pruneau Wayne State University For the Star Collaboration. STAR Data. Analysis Presented based on STAR TPC data.

marcosr
Download Presentation

Event by Event Fluctuations

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Topics in Heavy Ion Collisions, Montreal 2003 Event by Event Fluctuations • Pt Fluctuations • Balance Function • Net Charge Fluctuations • Conclusions Claude A Pruneau Wayne State University For the Star Collaboration

  2. STAR Data • Analysis Presented based on STAR TPC data. • Au + Au Collisions • At 20, 130, and 200 GeV. • p + p Collisions • At 200 GeV. • Analyses presented are by the STAR e-by-e group • Gary Westfall, MSU, • Sergei Voloshin, WSU, • CP, WSU C. A. Pruneau, HIC03.

  3. Pt Fluctuations • 1st order Phase Transition • Fluctuations in energy density due to the formation of QGP droplets. • 2nd order phase transitions • Divergence of Specific Heat • Increased fluctuations in energy density due to long range correlations. • Proximity to tri-critical and critical points would also lead to changes in fluctuation patterns. • Production of DCCs. • Jet Production • Fluctuations at “high pt”. C. A. Pruneau, HIC03.

  4. Determination of the Collision Centrality Based on multiplicity of charged particles in the STAR TPC Example: C. A. Pruneau, HIC03.

  5. Histograms of <pt> • Au+Au • 20 GeV & 200 GeV • 5% most central bin using min bias data • || < 1.0 • Solid lines are gamma distributions • Real Data wider than mixed • Non-statistical fluctuations C. A. Pruneau, HIC03.

  6. Definition of pt • Proposed by S. Mrowczynski, and M. Gazdzicki. • “Complicated” • Explicitly dependent on multiplicity, acceptance size, beam energy. • Correction for finite efficiencies are non trivial • May be misleading because of dependence on multiplicity and acceptance. • Checks only one hypothesis. C. A. Pruneau, HIC03.

  7. Definition of <pt,i pt,j> C. A. Pruneau, HIC03.

  8. <pt,i pt,j> vs Centrality and Acceptance C. A. Pruneau, HIC03.

  9. <pt,i pt,j> vs Centrality Comparison with HIJING and Mixed Events • || < 1.0 • Mixed events are zero • HIJING ~ 1/2 Data • “1/N” behavior C. A. Pruneau, HIC03.

  10. <N><pt,i pt,j> vs Centrality Comparison with HIJING and Mixed Events • Multiply by <N> • Not corrected for finite efficiency. • || < 1.0 • Looks similar to pt • |Mixed events| are zero. • HIJING approaches data in peripheral collisions C. A. Pruneau, HIC03.

  11. Pt Fluctuations - Conclusions • <pt,i pt,j> exhibits small beam energy dependence. • <pt,i pt,j> exhibits qualitative 1/N scaling with centrality. • Scaling is however not perfect. • <N><pt,i pt,j> depends on collision centrality • At variance with “predictions” based on HIJING. • Observation: Strengthening of the Correlation in central collisions! C. A. Pruneau, HIC03.

  12. Balance Functions at 200 GeV Basic Idea from Bass, Danielewicz, and Pratt [Phys. Rev. Lett. 85, 2689 (2000)] . • Au+Au at 130 GeV Results Published • J. Adams et al., PRL 90, 172301 (2003) • B() for all charged particles • B(y) for pions • Widths of the Balance Function • New Results – This talk • Au+Au, p+p at 200 GeV • B() for all charged particles • B(y) for pions and kaons • Widths of the Balance Function • Comparisons with HIJING and Mixed Events C. A. Pruneau, HIC03.

  13. Definition of the Balance Function Counts correlated charge/anti-charge pairs as a function of relative rapidity, y  |y2-y1| N+-(y) is calculated by histogramming y for all negative particles correlated with all positive particles in a given event and the resulting histogram is summed over all events, similarly for N++(y), N-+(y), and N--(y) N+(-) is the total number of positive(negative) particles summed over all events C. A. Pruneau, HIC03.

  14. Theoretical expectations • PYTHIA (p+p) shows a characteristic width of about 1 unit of y • Bjorken thermal model representing delayed hadronization shows narrower balance function width • Nucleon-nucleon wide • Delayed hadronization narrow C. A. Pruneau, HIC03. No STAR acceptance

  15. Balance Function for All Charged Pairs, Au+Au at 200 GeV no electrons Central Peripheral C. A. Pruneau, HIC03.

  16. Balance Function Widths, All Charged Particles C. A. Pruneau, HIC03.

  17. Balance Function Widths, p+p and Au+Au – 200 GeV Charged Pions All Charged Particles C. A. Pruneau, HIC03.

  18. Conclusions based on Balance function widths • Measured widths for Au+Au • scale smoothly to p+p as a function of Npart • Widths predicted by HIJING (Au+Au) • Show no centrality dependence • Consistent with Au+Au peripheral and p+p widths • Balance functions for Au+Au get narrower in more central collisions, • Stronger correlation • Consistent with the idea of delayed hadronization C. A. Pruneau, HIC03.

  19. Koch, Jeon et al. Asakawa et al. Heiselberg et al. Net Charge Fluctuations • Reduced variance: • D – variable : • Equilibrated system C. A. Pruneau, HIC03.

  20. Dynamical Net charge Fluctuations • Sensitive to net charge • Insensitive to volume fluctuations • Statistical Limit – Independent particle production. • Dynamical Fluctuations. Measured Quantity C. A. Pruneau, HIC03.

  21. Dynamical Fluctuations ISR data. Filled circles – sqrt(s) = 63 GeV 1-body density Integral Correlation 2-body density Differential Correlation C. A. Pruneau, HIC03.

  22. 130 GeV 200 GeV Net Charge Dynamical Fluctuations - Au+Au @ 130, 200 GeV 130 GeV : 180k events, 200 GeV : 900k events u+-dyn(|h|<0.5) vs. M (|h|<0.75) C. A. Pruneau, HIC03.

  23. Magnitude of the Dynamical Fluctuations Measurement: 5% most central collisions @ 130 GeV u+-,dyn = -0.00236 ± 0.00006 (stat) ± 0.00005 (syst) Charge conservation contribution: u+-,dyn = -0.00095 40% of measured fluctuations Perfect Correlation : u+-,dyn (MAX) = -0.0076 • Dynamical Fluctuations are FINITE, correlations are FINITE. • Correlations exceed values expected from charge conservation alone. • Observed Correlations amount to ~30% of Maximum Value (-4/N) C. A. Pruneau, HIC03.

  24. Dynamical Fluctuations Dependence on Centrality Au+Au @ 130 GeV Charge conservation HIJING Thermalized Resonance Gas QGP ~ -3 C. A. Pruneau, HIC03.

  25. 130 GeV 200 GeV N u+-dyn(|h|<0.5) Au+Au 130, 200 GeV Measurement Acceptance: |h| < 0.5; pt > 0.15 GeV/c; Df = 2p Poisson Charge conservation Resonance Gas C. A. Pruneau, HIC03.

  26. In collaboration with S. Gavin, C. Gale, et al URQMD Calculation • Finite centrality dependence! • But different from measurement! C. A. Pruneau, HIC03.

  27. Net Charge Fluctuations - Conclusions • Measured Fluctuations • Finite centrality dependence • Inconsistent with predictions of Strong Suppression in thermalized QGP. • Larger but near those expected for a thermalized resonance gas. • Magnitude in Qualitative Agreement with HIJING calculation but… • Data exhibit centrality dependence not present in HIJING. • Observed centrality dependence at variance with that predicted by URQMD. C. A. Pruneau, HIC03.

  28. Conclusions • Pt Fluctuations • Stronger Correlations in Central Collisions • Small Energy Dependence. • Balance Function • Narrowing of the Balance Function in Central Collisions. • I.e. Stronger Correlations in Central Collisions. • Consistent with “delayed hadronization”. • Net Charge Fluctuations are finite • Stronger Correlations in Central Collisions. • More or less consistent with Thermal Resonance Gas in Thermal Equilibrium. • Small Energy Dependence. • Common Themes • Stronger correlations (not weaker) in Central Collisions. • Behavior Contrary to What is expected from “final state”, rescattering. • Memory of pp “strings” is lost • Points to a change of “initial conditions”. C. A. Pruneau, HIC03.

  29. Backup Slides C. A. Pruneau, HIC03.

  30. Charge Conservation Effects • Assume N- created +/- pairs, the 2-particle density can be written: • One finds • Charge conservation contribution to dynamic fluctuations • At RHIC (130 GeV), based on total charged particle multiplicities published by PHOBOS (|h|<5.6), one expects : uAA,dyn= -0.00095 C. A. Pruneau, HIC03.

  31. Dynamical Fluctuations Properties C. P., S. Gavin, and S. Voloshin, nucl-ex/0204011, PRC 66 (2002).] Independent of volumefluctuationsIndependent Particle Production Collision Dynamics Independent of collisioncentrality Robust Observable(Independent of efficiency) Charge Conservation Perfect N+=N- correlation C. A. Pruneau, HIC03.

  32. C. P., S. Gavin, and S. Voloshin, nucl-ex/0204011, PRC 66 (2002).] Relationship to other Fluctuation Observables Observable Definition Relationship(s) “F-Measure” RHIC Central Rapidities Reduced Variance “D-Measure” C. A. Pruneau, HIC03.

  33. Au+Au @ 130 GeV Dynamical Fluctuations Dependence on Rapidity Acceptance Charge conservation • Slow variation with size of acceptance. • Tends towards charge conservation limit for largest acceptance. C. A. Pruneau, HIC03.

  34. PHENIX Au+Au Result @ 130 GeV From nucl-ex/0203014, PRL 86 (2001) 3500, and J. Nystrand – private communication • Measurement: 10% most central collisions • Detector Acceptance: • |h| < 0.35 • pt > 0.2 GeV/c • Df = p/2 • <Nch>=79 • MESSAGES : • Efficiency Corrections Are Needed • Different Azimuthal Acceptance but… • Qualitative Agreement with STAR measurement • STAR : u+-,dyn = -0.00236 ± 0.00006 (stat) ± 0.00005 (syst) • PHENIX : u+-,dyn = -0.0018 ± 0.0004 (stat) –0.0027 (syst) wQ = 0.965 ± 0.007 (stat) – 0.019 (syst) u+-,dyn = -0.0018 ± 0.0004 (stat) –0.0027 (syst) D = 3.2 ± 0.16 (stat) – 0.5 (syst) F = -0.143 ± 0.02 (stat) – 0.06(syst) |h| < 0.5 Df = 2p My calculation C. A. Pruneau, HIC03.

  35. C. A. Pruneau, HIC03.

  36. Motivation: Delayed Hadronization • Bass, Danielewicz, and Pratt [Phys. Rev. Lett. 85, 2689 (2000)] . • Basic premise: charge/anti-charge pairs are created close together in space-time • Pairs if created early in the collision • will be pulled apart in rapidity by longitudinal expansion • will suffer scattering for the duration of the collision, • losing their correlation in rapidity • If instead, the system exists in a deconfined phase for a substantial time, pairs formed at hadronization, • will experience less expansion and fewer collisions, • retaining more of their correlation in rapidity C. A. Pruneau, HIC03.

  37. Strategy • Measure B() and B(y)for Au+Au and p+p collisions at 200 GeV. • In peripheral Au+Au collisions, expect behavior that is similar to nucleon-nucleon scattering. • Measure whether central Au+Au collisions show any difference from peripheral collisions or p+p • Use the width of the balance function to quantify centrality dependence. • Compare with centrality dependence of HIJING. C. A. Pruneau, HIC03.

  38. Balance Function for Pion Pairs, Au+Au at 200 GeV p < 0.7 GeV, no electrons Identified charged pion pairs (+,-) Central Peripheral C. A. Pruneau, HIC03.

  39. Balance Function for p+p at 200 GeV All Charged Particle Pairs Charged Pion Pairs C. A. Pruneau, HIC03.

  40. C. A. Pruneau, HIC03.

More Related