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Fluctuations and Correlations in Relativistic Heavy Ion Collisions

Jeffery T. Mitchell (Brookhaven National Laboratory). Fluctuations and Correlations in Relativistic Heavy Ion Collisions. Outline: Charge Fluctuations Balance Functions Event-by-event <p T > Fluctuations Looking Ahead Conclusions, Credits, Apologies. Charge Fluctuations.

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Fluctuations and Correlations in Relativistic Heavy Ion Collisions

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  1. Jeffery T. Mitchell (Brookhaven National Laboratory) Fluctuations and Correlations in Relativistic Heavy Ion Collisions • Outline: • Charge Fluctuations • Balance Functions • Event-by-event <pT> Fluctuations • Looking Ahead • Conclusions, Credits, Apologies Jeffery T. Mitchell (BNL) – QM2004

  2. Charge Fluctuations Hypothesis: Fluctuations in net charge and net baryon number may be significantly reduced if a QGP is formed in the collisions Asakawa, Heinz, Müller PRL 85(2000)2072; Jeon & Koch PRL 85(2000)2076 Fractional electric charges of the quarks ==> Charges more evenly spread in a plasma ==> Reduced net charge fluctuations in a small region of phase-space Hadron Gas Scenario Quark-Gluon Plasma Scenario Jeffery T. Mitchell (BNL) – QM2004

  3. Summary of Charge Fluctuation Measures Quoted in this presentation Jeffery T. Mitchell (BNL) – QM2004

  4. Charge Fluctuation Magnitude Expectations Jeffery T. Mitchell (BNL) – QM2004

  5. Charge Fluctuations vs. Rapidity Acceptance (Excitation Function): NA49 Charge Conservation Correction for fluctuations due to charge conservation. Quark Coalescence Resonance Gas Quark-Gluon Plasma Also see talk by H. Sako for new CERES results. See poster by P. Chrisakogiou Jeffery T. Mitchell (BNL) – QM2004

  6. Charge Fluctuations vs. Rapidity Acceptance Phys. Rev. Lett. 89 (2002) 082301, 130 GeV.  = /2, 0.3  pT  2.0 GeV/c Charge Conservation Quark Coalescence Resonance Gas Quark-Gluon Plasma Jeffery T. Mitchell (BNL) – QM2004

  7. Charge Fluctuations vs. Rapidity Acceptance Phys. Rev. C68 (2003) 044905, 130 GeV. Charge Conservation Quark Coalescence Resonance Gas Quark-Gluon Plasma Jeffery T. Mitchell (BNL) – QM2004

  8. Balance Functions Bass, Danielewicz, & Pratt, Phys. Rev. Lett. 85, 2689 (2000) N+ - (Dy)= Histogram of | y(p+) - y(p--) |, for all possible pairs within an event. This histogram is summed over all events. • Designed to determine whether hadronization from a QGP occurs early (<1 fm/c) or late. • Based upon the fact that charge is conserved locally, and produced pairs are initially correlated in coordinate space. • Bottom line: The balance function is narrower in the delayed hadronization scenario. Early hadronization scenario: Pairs separate in rapidity due to expansion and rescattering. Delayed hadronization scenario: Pairs are more strongly correlated in rapidity. Jeffery T. Mitchell (BNL) – QM2004

  9. STAR 130 GeV Balance Function Results Phys. Rev. Lett. 90 (2003) 172301. Identified Pion Pairs All Charged Hadron Pairs Identified Pion Pairs All Charged Hadron Pairs Jeffery T. Mitchell (BNL) – QM2004

  10. STAR 200 GeV Balance Function Widths The balance function gets narrower in central collisions  Delayed hadronization scenario? See talk tomorrow by G. Westfall Increasing Centrality Jeffery T. Mitchell (BNL) – QM2004

  11. NA49 17 GeV Balance Function Widths Preliminary See talk by M. Gazdzicki A similar behavior AND narrowing magnitude is observed compared to the STAR data! The balance function gets narrower in central collisions. Increasing Centrality Jeffery T. Mitchell (BNL) – QM2004

  12. Other explanations for the broadening of the balance function Resonance contributions P. Bozek, W. Broniowski, and W. Florkowski, nucl-th/0310062 Computing balance functions in a thermal model with neutral resonance decay. The calculations including resonances are consistent with the STAR results. • Quark Coalescence Model Predictions • Bialas, hep-ph/0308245. • Predicts a width consistent with the STAR result for central collisions with a transverse flow velocity below 0.5c. 0-10% centrality 10-40% centrality 40-70% centrality 70-96% centrality Jeffery T. Mitchell (BNL) – QM2004

  13. <pT> Fluctuations: Probing for Signs of a Phase Transition Analogy: Critical Opalescence M. Stephanov et al., Phys. Rev. Lett. 81 (1998) 4816: Suggest that near a tri-critical end-point in the QCD phase diagram, event-by-event fluctuations in average pT could increase significantly. B. Berdnikov and K. Rajagopal, Phys. Rev. D61 (2000) 105017: Estimate that the effect could be a 10-20% increase in average pT fluctuations. Movie of a sealed container containing freon on a hot plate at the critical point. The image is projected onto a wall. Movie by the University of Minnesota Physics Department Jeffery T. Mitchell (BNL) – QM2004

  14. Behold The Signal! Jeffery T. Mitchell (BNL) – QM2004

  15. Summary of Event-by-event <pT> Fluctuation Measures FpT Goal of the observables: State a comparison to the expectation of statistically independent particle emission. s2pT,dyn DspT,n Quoted in this presentation FpT SpT Jeffery T. Mitchell (BNL) – QM2004

  16. How To Measure A Fluctuation Gamma distribution calculation for statistically independent particle emission with input parameters taken from the inclusive spectra. See M. Tannenbaum, Phys. Lett. B498 (2001) 29. Red: Random Expectation (G distribution) Blue: STAR acceptance fluctuation of: fpT=52.6 MeV, FpT=14%, s2pT,dyn=52.3 (MeV/c2), SpT=9.8% MpT = Event-by-Event Average pT Jeffery T. Mitchell (BNL) – QM2004

  17. A Positive Signal is Observed!Known contributions to the <pT> fluctuation signal should be subtracted. Contributions from Known Processes • HBT – too small (NA49, STAR, CERES) • Resonances – too small (NA49, STAR) • Elliptic Flow – too small/negligible (PHENIX, CERES, NA49) • Hard Processes… • Or onset of thermalization… A Schematic Illustration of Elliptic Flow Jeffery T. Mitchell (BNL) – QM2004

  18. A Possible Explanation of the Signal: A System in Near-local Thermal Equilibrium Sean Gavin, nucl-th/0308067, see his talk tomorrow for more details. Jeffery T. Mitchell (BNL) – QM2004

  19. The onset of thermalization? See talks tomorrow by S. Gavin (model) and G. Westfall (data) Jeffery T. Mitchell (BNL) – QM2004

  20. A Large Fluctuation Contribution at high pT 0.2 < pT < pTmax 0.1 < pT < pTmax Preliminary See talk by M. Tannenbaum 20-30% centrality 20-25% centrality See talk by H. Sako An increase in observed fluctuations grows primarily in a pT region where number fluctuations vary little. This trend is observed at all centralities. Increases from pTmax=1.0 to 2.0 GeV/c PHENIX Fluctuations: 243% CERES Fluctuations: 34% <N>: < 15% Jeffery T. Mitchell (BNL) – QM2004

  21. Fluctuations: A Jet Contribution? A Schematic Illustration of Jet Suppression Jets inherently add particles that are correlated in pT to the event, so a contribution due to hard processes is expected, but how much? What about jet suppression? Jeffery T. Mitchell (BNL) – QM2004

  22. Results from a 2-component hybrid simulation. Component 1: Reproduce soft processes by sampling the inclusive pT and N data distributions. Component 2: Embed PYTHIA hard scattering events at a given rate per particle produced in Part 1. Keep the rate fixed, or scale it by RAA. Jet Simulation Results: PHENIX at 200 GeV PHENIX Data: nucl-ex/0310005 This decrease is due to the signal competing with the MpT width increase for low N. This decrease is due to jet suppression? See poster by J. T. Mitchell 20-25% centrality Jeffery T. Mitchell (BNL) – QM2004

  23. Jet Simulation Results: STAR at 130 GeV STAR data: nucl-ex/0308033 Error bars are the quoted total systematic error. The simulation predicts ~15-20% increase when going from 130 to 200 GeV Jeffery T. Mitchell (BNL) – QM2004

  24. Jet Simulation Results: NA49 at 17 GeV NA49 Preliminary Data: See poster by K. Grebieszkow & M. Rybczynski Jeffery T. Mitchell (BNL) – QM2004

  25. Estimate of the Magnitude of Residual Event-by-Event Temperature Fluctuations R. Korus and S. Mrowczynski, Phys. Rev. C64 (2001) 054908. p inclusive pT, G(p,b), p~1 Jeffery T. Mitchell (BNL) – QM2004

  26. Add a dimension: 2-point transverse momentum correlations Higher ptpairs from hard scattering ? NA49 17 GeV Pb+Pb STAR Preliminary 130 GeV Au+Au Data s(T) = 5 MeV Like sign Thermal Fluctuation Model Simulations s(T) = 10 MeV s(T) = 20 MeV STAR Preliminary hep-ex/0311009 L. Ray, DNP 2003, see his poster HBT and Coulomb interaction In PHENIX, x(1.5 GeV/c) ~ 0.93 Jeffery T. Mitchell (BNL) – QM2004

  27. Coming Soon: A Multi-dimensional Analysis (centrality, pT,1, pT,2, pseudorapidity, azimuth) T. Trainor, DNP 2003 STAR Preliminary See poster by D. Prindle Same side Opposite side Elliptic flow has been removed. Jeffery T. Mitchell (BNL) – QM2004

  28. Synopsis • Charge fluctuations: • SPS results and RHIC-PHENIX results are close to the random expectation after correcting for charge conservation. • RHIC-STAR results are consistent with a quark coalescence model prediction in central collisions. • Balance Functions: • Both SPS (NA49) and RHIC (STAR) results show a narrowing of the balance function in central collisions. • The narrowing is indicative of delayed hadronization. • The narrowing may also be explained within the quark coalescence picture, or by resonance decay contributions. • <pT> Fluctuations: • A positive fluctuation signal that decreases for more central collisions is seen at the SPS and at RHIC. • The signal can be explained within a model that simulates jet production, however, a jet suppression scenario must be introduced to describe the most central collisions at RHIC. • The signal can also be explained within a thermalization onset scenario. • Stay tuned for more exciting results soon! Jeffery T. Mitchell (BNL) – QM2004

  29. But wait! There’s more! Acknowledgements The following topics could not be covered in this presentation. • Multiplicity Fluctuations • Spatial Fluctuations, or “Event Texture” • Charge/Neutral (Isospin) Fluctuations • Particle Ratio Fluctuations Many thanks to H. Appelshauser (CERES), M. Gazdzicki (NA49), S. Gavin, D. Prindle (STAR), L. Ray (STAR), C. Roland (NA49), H. Sako (CERES), T. Trainor (STAR), G. Westfall (STAR), for providing input into this presentation. Jeffery T. Mitchell (BNL) – QM2004

  30. Auxiliary Slide Fluctuations According to HIJING 20-25% centrality HIJING cannot reproduce the centrality dependence of the fluctuations. One problem is that <N> changes depending on the HIJING settings – not matched to the observed dataset. Example for 0-5% centrality: <N> = 93.0 for jet suppression, 76.6 without suppression, and 51.2 without jets. Jeffery T. Mitchell (BNL) – QM2004

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