Event-by-Event Fluctuations in Transport Models

1. Event-by-Event Fluctuations in Transport Models Marcus Bleicher Institut für Theoretische Physik Goethe Universität Frankfurt Germany Marcus Bleicher, VI-SIM 2005

2. Outline of the talk • Introduction • Ratio fluctuations • Charge correlations • Baryon-strangeness correlations • Scaled variance  Elena Bratkovskaya • Summary Marcus Bleicher, VI-SIM 2005

3. Motivation At RHIC: look for signals of freely moving partons.At SPS:look for the mixed phase and the onset of deconfinement E. Bratkovskaya et al., PRC 2005 Marcus Bleicher, VI-SIM 2005

4. What can transport models do? • Provide baseline calculations,including resonances, jets, flow,…Study energy/centrality dependence • Study acceptance effects, i.e. how does limited detector coverage influence the results Marcus Bleicher, VI-SIM 2005

5. Sources of fluctuations I • Centrality determination- same volume?- same energy deposition?- same particle density? • Number of (initial) collisions- elastic vs inelastic • Collision energy spectrum of the individual collisions Marcus Bleicher, VI-SIM 2005

6. Fluctuations/Correlations II • String mass: P(m2)~1/m2Multiplicity fluctuations at fixed Ecm • Fluctuations of string tension (A. Bialas 2000)strangeness and pT fluctuations • Resonance decays • Flow • Jets Marcus Bleicher, VI-SIM 2005

7. Fluctuations are everywhere • Au+Au at RHIC • Strong fluctuations of initial state eccentricity Marcus Bleicher, VI-SIM 2005

8. Fluctuations are everywhere • Au+Au at RHIC • Strong fluctuations of final elliptic flow Zhu, Bleicher, Stoecker, nucl-th/0509081 Marcus Bleicher, VI-SIM 2005

9. Marcus Bleicher, VI-SIM 2005

10. Energy density fluctuations Pb(160AGeV)+Pb • Hot spots in the ‘thermal’ energy density • ‘Clusters’ of size ~ 5 fm3 e (GeV/fm3) X (fm) y (fm) Dz=1fm M. Bleicher et al, Nucl.Phys.A638:391,1998 Marcus Bleicher, VI-SIM 2005

11. Low pT correlations • Idea: find predicted enhancement of low momentum modes, e.g. due to DCCs • Use factorial moments to investigate different low pT behavior Marcus Bleicher, VI-SIM 2005

12. Factorial moments and DCCs Bleicher, Randrup, Snellings, Wang, Phys.Rev.C62:041901,2000 Marcus Bleicher, VI-SIM 2005

13. Ratio fluctuations • proposed by Jeon, Koch, Mueller, Asakawa… (2000) • E.g. Marcus Bleicher, VI-SIM 2005

14. The ‘famous’ D: The first smoking gun prediction Bleicher, Jeon, Koch, PRC (2000) Marcus Bleicher, VI-SIM 2005

15. Similar results from other models Marcus Bleicher, VI-SIM 2005 Zhang, Topor Pop, Jeon, Gale, hep-ph/0202057

16. and why it doesn’t work • Hadronization (quark recombination) destroys the fluctuation • Finite acceptance might also destroy the signal (Zaranek et al.) qMD calculation by S. Scherrer Marcus Bleicher, VI-SIM 2005

17. Fluctuation studies: Ratios • K/p fluctuations increase towards lower beam energy • Significant enhancement over hadronic cascade model • p/p fluctuations are negative • indicates a strong contribution from resonance decays Taken from Christoph Roland NA49 Preliminary NA49 Preliminary Marcus Bleicher, VI-SIM 2005

18. Charge correlations: the idea: • Creation of QGP blob around midrapiditysurrounded by a hadron gas • Different charge correlation lengths giin QGP and hadron gas  try to measure the charge correlation length in rapidity Shi and Jeon, hep-ph/0503085 Marcus Bleicher, VI-SIM 2005

19. How to do it QF/B is net charge forward/backward of y k is proportional to the charge correlation length Thomas, Chao, Quigg, PRD7,PRD9 (1973/1974) Marcus Bleicher, VI-SIM 2005

20. What do transport models say • k does not depend on rapidity in HIJINGconstant charge correlation length Marcus Bleicher, VI-SIM 2005

21. Is the signal robust? Au+Au at 200 AGeV kbar means restricted to |eta|<1 Marcus Bleicher, VI-SIM 2005

22. Baryon-Strangeness Correlations I Definition: Idea: Strangeness and baryon numbercarriers are different in QGP and hadron gas. First suggested by V. Koch et al., 2005 • HG: strangeness is decoupled from baryon number (mesons)  small CBS correlation • QGP: strangeness is fixed to baryon number (strange quark) large CBS correlation Marcus Bleicher, VI-SIM 2005

23. Baryon-Strangeness Correlations 2 • Limiting cases for CBS: • Large mB: CBS3/2 • large acc. window: CBS0Explored with help of increasing rapidity window inAu+Au reaction at RHIC • Present models yield similar results for small rapidity window • Different handling of the fragmentation region/spectators influences results at large rapidities Haussler, Stoecker, Bleicher,hep-ph/0507189 Marcus Bleicher, VI-SIM 2005

24. Baryon-Strangeness Correlations 3 Energy dependence of CBS allows to study the onset of deconfinement transition Note that the QGP result is for m=0 Here |ymax|<0.5 • Deviations from the HG are expected around high SPS energy region, due to QGP onset. Haussler, Stoecker, Bleicher,hep-ph/0507189 Marcus Bleicher, VI-SIM 2005

25. Baryon-Strangeness Correlations 4 Centrality dependence of CBS allows to study the critical volume needed for QGP formation. Note that the QGP result is for m=0 |ymax|<0.5, Ecm=200AGeV • Hadron-string transport models predict no centrality dependence of CBS • A QGP transition leads to a strong centrality dependence Haussler, Stoecker, Bleicher,hep-ph/0507189 Marcus Bleicher, VI-SIM 2005

26. Summary • The D puzzle is solved: hadronization destroys all initial state correlations • Dynamical fluctuation of K/p increase towards 20 AGeV beam energy (not present in hadron-string models) • Charge correlations might allow to probe QGP formation in a limited rapidity interval • Baryon-strangeness correlations allow to pin down the onset of the QGP transition. • Fluctuations and correlations are valuable tools to study heavy ion reactions. • However, the interpretation is usually difficult. Marcus Bleicher, VI-SIM 2005

27. Thanks • Diana Schumacher • Hannah Petersen • Stephane Haussler • Diana Schumacher • Elena Bratkovskaya • Manuel Reiter • Sascha Vogel • Xianglei Zhu • Horst Stoecker Marcus Bleicher, VI-SIM 2005