1. Marcus Bleicher, Florence 2006 Longitudinal Flow and Onset of Deconfinement Marcus Bleicher Institut für Theoretische Physik Goethe Universität Frankfurt Germany

2. Marcus Bleicher, Florence 2006 Outline of the talk Introduction Fluctuations  Evidence for mixing Rapidity widths + Landau  softest point Summary

3. Marcus Bleicher, Florence 2006 The tool: UrQMD v2.2 Non-equilibrium transport model Hadrons and resonances String excitation and fragmentation Cross sections are parameterized via AQM or calculated by detailed balance pQCD hard scattering at high energies Generates full space-time dynamics of hadrons and strings

4. Marcus Bleicher, Florence 2006 Thanks to the UrQMD group @ Frankfurt Sascha Vogel (Resonances) Stephane Haussler (Event-by-Event Fluctuations) Hannah Petersen (Flow at FAIR) Diana Schumacher (Di-Leptons) Qingfeng Li (Isospin Dynamics & HBT) Xianglei Zhu (Elliptic Flow and Charm) Mohamed Abdel-Aziz (Event-by-Event Fluctuations) Elena Bratkovskaya (HSD) and Horst Stoecker (keeping it running)

5. Marcus Bleicher, Florence 2006 Motivation At RHIC: look for signals of freely moving partons. At FAIR/SPS: look for the mixed phase and the onset of deconfinement E. Bratkovskaya, M.Bleicher. et al., PRC 2005

6. Marcus Bleicher, Florence 2006 Excitation functions: ratios ‘Horn’ in the ratio not reproduced well reproduced relative strange baryon enhancement reproduced E. Bratkovskaya, M.Bleicher. et al., PRC 2005

7. Marcus Bleicher, Florence 2006 K/  fluctuations increase towards lower beam energy –Significant enhancement over hadronic cascade model p/  fluctuations are negative –indicates a strong contribution from resonance decays NA49 Preliminary Fluctuation studies Taken from Christoph Roland

8. Marcus Bleicher, Florence 2006 Energy dependence H. Petersen, X. Zhu, M.B. Qualitative description OK Importance of potentials at low energies Lack of pressure shows up at SPS energies EoS Flow

9. Marcus Bleicher, Florence 2006 ‘Partonic’ dof already at low SPS energy Breakdown of v2 in model coincides with onset of ‘partonic’ matter  signals onset of change of EoS in the early stage 30 AGeV H. Petersen, X. Zhu, M.B.

10. Marcus Bleicher, Florence 2006 Stopping power Linear increase of rapidity shift at low energies ‘Saturation’ above highest SPS energy However, relative momentum loss is energy independent UrQMD vs data Pb+Pb/Au+Au

11. Marcus Bleicher, Florence 2006 Multiplicities Temperatures Elliptic Flow Correlations have already been studied Can we learn more from the longitudinal dynamics?

12. Marcus Bleicher, Florence 2006 Multiplicity fluctuations Extraction of the multiplicity distribution for every N par Note: Calculation is narrower than the data for N par ~45 Pb+Pb (158 AGeV) in the NA49 acceptance (1.1<y CM <2.9)

13. Marcus Bleicher, Florence 2006 The fluctuation is quantified with the scaled variance : Enhanced fluctuations for mid- peripheral collisions are observed Multiplicity fluctuations at SPS: The problem Note : - for a poisson distribution, w=1 Similar results from HIJING, HSD and RQMD

14. Marcus Bleicher, Florence 2006 Where is the problem? Pb+Pb (158 AGeV) in the NA49 acceptance (1.1<y CM <2.9) Mean value correctly reproduced Variance reproduced for central and very peripheral events Failure for mid-peripheral events

15. Marcus Bleicher, Florence 2006 Analysis of different windows the normalized variance : flat in the projectile hemisphere larger in the mirror acceptance even larger in 4  maximum around N p =40 Konchakovski, Haussler,…, PRC 73 (2006)

16. Marcus Bleicher, Florence 2006 Fluctutions in target region the fluctuation has a maximum around N p =25 introduces an asymetry between projectile and target participants leads to an increase of the multiplicity fluctuation in the target hemisphere

17. Marcus Bleicher, Florence 2006 Correlation length in rapidity Rapidity window dependence : correlation length of the order of 1 unit of rapidity target and projectile hemisphere are independent in hadron-string models

18. Marcus Bleicher, Florence 2006 Mixing and fluctuations M. Gazdzicki and M. Gorenstein: arXiv:hep-ph/0511058 I.e. the trigger condition ‘marks’ projectile and target participants This allows to study the degree of mixing of the matter produced in HIC Data suggest strong mixing of hemispheres Hints to expanding initial fireball in contrast to string dynamics

19. Marcus Bleicher, Florence 2006 What the fluctuations told us… Initial fireball of newly produced particles Fireball seems to expand Landau-like Leads to strong correlations in rapidity We might use Landau-type hydro to explore the properties of this matter

20. Marcus Bleicher, Florence 2006 Pion rapidity density Pions rapidity densities are Gaussians at all energies D. Ouerdane, QM04

21. Marcus Bleicher, Florence 2006 Different particle types NA49 data yields Gaussian rapidity distributions Also ALL other experiments report Gaussians for newly produced particles

22. Marcus Bleicher, Florence 2006 Fireball expansion Assumptions: - applies only to newly produced particles - Lorentz contracted nuclei - simplified Hagedorn gas EoS E. Shuryak, Yad. Fiz. 16 (1972) 395 similar to Landau hydro For more praise on Landau hydro see. P. Steinberg

23. Marcus Bleicher, Florence 2006 Rapidity widths Rapidity width scales linearly with projectile rapidity M. Bleicher, hep-ph/0509314

24. Marcus Bleicher, Florence 2006 Speed of sound Analysis of the rapidity data indicates a softest point at 20-30 AGeV beam energy M. Bleicher, hep-ph/0509314

25. Marcus Bleicher, Florence 2006 Its soft, but… …is it the mixed phase? UrQMD also describes the rapidity widths UrQMD has a soft equation of state

26. Marcus Bleicher, Florence 2006 Summary Fluctuations indicate strongly mixed initial stage Assumption of Landau-type hydro allows to extract speed of sound from rapidity widths Apparent local minimum of sound velocity around 20 – 30 AGeV Nature of this softest point is unclear