What is SO special about strangeness in heavy ion collisions ?

1. What is SO special about strangeness in heavy ion collisions ? Rene Bellwied Wayne State University 7th International Conference on Strangeness in Quark Matter North Beach, March 12-17, 2003

2. A connection to cosmology • Essential: Witten’s ‘Cosmic Separation of phases’ (Phys.Rev.D 30 (1984) 272) and his idea of strange quark matter. • The impact on cosmology might be far reaching and definitely affected the search for strangeness enhancement in general and strange quark matter in particular (see Jack Sandweiss talk). • Strange Quark Matter is still considered a possibility for stable or metastable matter in the universe.

3. Two recent examples in astrophysics Fundamental paper on ‘How to identify a strange star’ by Jes Madsen, PRL 81 (1998) 3311 Recent measurements by Drake et al. and Helfand et al. in 2002 with the Chandra X-ray telescope (see Markus Thoma’s talk) These two NASA Chandra X-ray Observatory images show two stars - one too small, one too cold - that reveal cracks in our understanding of the structure of matter. (AFP) 3C58 RXJ1856

4. Did quark matter strike the earth ? Two anomalous seismic events occurred in 1993, and were measured independently by 9 monitoring stations. Strange quark matter should pass through the earth at 400 km/s (40 times the speed of seismic waves), i.e. search for seismic events not connected with traditional seismic disturbances e.g. earth quakes. (Herrin et al., SMU, 2002)

5. What can we do in the laboratory ? The idea of strange quark matter did not only initiate strangelet searches (see Jack’s talk) but led also to potential signatures for the QGP phase transition. Increasing strangeness enhancement as a signal for QGP and strangeness equilibration as a signal for thermalization of the particle emitting source were for years at the forefront of our research.

6. Early 80’s: Strangeness enhancement (K/p and later anti-baryon/baryon as function of beam energy (Rafelski, Mueller, Koch et al.) • Late 80’s: Strangeness equilibration (strangeness production in thermal models as signal for phase equilibration and collective flow) • 1990’s: Strangeness enhancement (multistrange antibaryons as function of system size and beam energy) Re-invent strangeness as a QGP signature • 2000’s: parton quenching (strange particles as leading jet particles), timescales (strange resonances), fluctuations (strange particles e-by-e), partonic flow (radial and elliptic flow of strange particles)

7. K/p K+/K- [GeV] History of strangeness enhancement • K/p – the benchmark for abundant strangeness production:

8. STAR preliminary STAR preliminary The impact of baryon density • K-/K+ – is a simple function of baryon density see talk by M.Velkovsky

9. NA49: volume effects (saturation ?) • Compare: different system sizes at common incident energy • Search for better scaling variable than Npart • Good measure: mean collision density in space and time (UrQMD simulation) See talks by Ingrid Kraus & Jean Cleymans

10. Lines of constant lS I. Increase instrange/non-strangeparticle ratios PBM et al., hep-ph/0106066 total II. Maximum isreached mesons III. Ratios decrease (Strange baryonsaffected more stronglythan strange mesons) baryons hidden strangeness mesons <E>/<N> = 1 GeV Peaks at 30 A GeV in AA collisions due to strong mB dependence Wroblewski factor evolution dependent on T and mB dominated by Kaons Wroblewski factor

11. 4p yields mid-rapidity yields Experimental L/p

12. new European ‘can-do-all’ facility see talk by H.Gutbrod New machines to explore the high density regime A new European heavy-ion and anti-proton machine A complementary high energy hadron facility in Japan (JHF)

13. Strangeness enhancement in B/B ratios • Baryon over antibaryon production can be a QGP signature as long as the baryochemical potential is high (Rafelski & Koch, Z.Phys. 1988) • With diminishing baryochemical potential (increasing transparency) the ratios approach unity with or without QGP, and thus only probe the net baryon density at RHIC.

14. STAR p+p 200 GeV BRAHMS, PRL nucl-ex/0207006 STAR preliminary New RHIC data of baryon ratios See talk by J.H.Lee • The ratios for pp and AA at 130 and 200 GeV are almost indistinguishable. The baryochemical potentials drop from SPS to RHIC by almost an order of magnitude to ~50 MeV at 130 GeV and ~20 MeV at 200 GeV.

15. equilibration volume ? STAR Preliminary Tounsi et al. Strangeness enhancement in yields • Enhancement factors up to 20 (!) comparing pp to AA for W. Still very large centrality dependence for W. See talks by C.Meurer, M.Mitrovski, L.Sandor

16. Is strangeness still enhanced at RHIC ? • Anti-strange baryon production is a measure of enhancement, whereas strange baryon production at RHIC is strongly affected by vanishing net baryon density NA49 preliminary

17. Strangeness thermalization: Doyields (ratios) agree with the statistical model picture ?

18. Are thermal models boring ? Good success with thermal models in e+e-, pp, and AA collisions. Thermal models generally make tell us nothing about QGP, but (e.g. PBM et al., nucl-th/0112051): Elementary particle collisions: canonical description, i.e. local quantum number conservation (e.g.strangeness) over small volume. Heavy ion collisions: grand-canonical description, i.e. percolation of strangeness over large volumes, most likely in deconfined phase if chemical freeze-out is close to phase boundary.

19. Do we understand strangeness production ? • Chemical (and thermal) equilibrium models describe the data, so do non-equilibrium models ! Is equilibrium an applicable concept ? (see QM round table discussion) • Even if we assume thermal equilibrium, do we understand production on a microscopic (partonic) level ? Not really.

20. Radial flow and thermalization ? STAR preliminary STAR preliminary see Javier Castillo’s talk

21. Common parametrization of flow ? • Blast wave parametrization fits for NA49 & STAR • Do particles with smaller interaction cross section decouple earlier and still show transverse flow ? , STAR preliminary ,K,P, NA49 – PbPb 158 A GeV

22. Particle identified elliptic flow • v2 measurements: p, k, p, L flow, do X and W flow ? STAR preliminary see talk by Paul Sorensen

23. RHIC Particle Spectra at 200 GeV BRAHMS: 10% central PHOBOS: 10% PHENIX: 5% STAR: 5% see PHOBOS talk by Gabor Veres

24. preliminary preliminary One sees the mass dependence of the transverse expansion, which is well described by thermal and hydrodynamics models Strangeness pushing the boundaries of particle identification

25. Strange jet-like particles • R(AA) & v2 measurements in Au-Au (see talks by Hui Long, Paul Sorensen and Julia Velkovska) Effects due to: initial state (gluon saturation) or final state (partonic energy loss, quark coalescence, hadronic/partonic flow) ? Is there a mass dependence or a flavor dependence ? Note: L show no suppression out to 3 GeV/c (similar to PHENIX protons and D-mesons)

26. L+Lbar/K0s preliminary Interplay between soft and hard processes (Vitev et al., QM 2002) see talks by B.Norman and H.Long

27. Strange resonances in medium Short life time [fm/c] K* < *< (1520) <  4 < 6 < 13 < 40 see talks by: L. Gaudichet H. Zhang J. Ma P. Fachini D. Jouan Rescattering vs. Regeneration ? Red: before chemical freeze out Blue: after chemical freeze out Medium effects on resonance and their decay products before (inelastic) and after chemical freeze out (elastic).

28. STAR preliminary     Giorgio Torrieri and Johann Rafelski Phys.Lett.B509:239-245, 2001 Resonances come into their own • Resonances tells us about production, rescattering, and regeneration & medium modifications • Resonances tell us about timescales (together with balance functions & HBT measurements)

29. f-measurements at SPS & RHIC • The f is interesting in terms of thermal radial flow and in terms of medium modifications. • NA50 / NA 49 difference due to different decay channels (i.e. medium modifications) ? PHENIX will do precision measurement in the K+K- and the e+e--channels see J.Ma’s talk

30. 4.0 3.0 L / p 2.0 1.0 Some puzzles along the way AGS: measured by E864/E878 confirmed by E917 SPS: measured by NA49 RHIC: measured by STAR Large ratio at AGS (and SPS) still not understood

31. Sub-threshold Kaon production (KaOS) see Andreas Foerster, Laura Tolos & Christoph Hartnack talks

32. Recent non-RHIC measurement X production in Au-Au collisions at 6 A GeV (E895@AGS) see Paul Chung’s talk

33. Future measurement of interest • Hyperon polarization in AA:L is measured (E896 @ AGS) and in agreement with pp and pA data, but pp and pA data from FNAL show intriguing differences between L,X,W and their antiparticles

34. STAR p+p 200 GeV STAR preliminary STAR preliminary STAR preliminary What did we learn in pp ? see talks by: A. Billmeier, R. Witt & posters by: M.Heinz and J.Adams

35. a.) as reference for strangeness enhancement & production mechanisms b.) as reference for high pt phenomena: (Cronin, jet quenching, quark coalescence) P.B. Straub et al., PRL 68 (1992) FNAL experiments measuring R (W / Be) for identified particles at Ös of 27.4 and 51.3 GeV. What is to come in pA ? use particle identified strange particle spectra from the RHIC dA run:

36. Main topics for the ‘new’strangeness • Can we prove that we have buildup of transverse and elliptic flow in the partonic phase by measuring multistrange baryon elliptic, transverse, and directed flow ? • Can we show that high pt particle suppression (measured through R(AA), v2, and back-to-back jets) is due to final state effects (e.g. quenching in the QGP) and that these effects are flavor and/or mass dependent by measuring K+,K-,K0, L, L-bar, X, X-bar R(AA) functions ? • Can we determine timescales for all phases of the collision and quantify medium modifications by precisely measuring the generation, rescattering, and regeneration of strange resonances ? • We need pp and pA reactions for reference

37. We have come a long way ! 4th SQM 98, Padova, RHIC summary talk: Yes !?! Well, maybe …. Let’s just wait and see ! Yeah ! Heck, YEAH !!

38. Old ‘smoking guns’ (e.g. strangeness enhancement) get replaced by new ‘smoking guns’ (e.g. strangeness quenching and flow). There will be plenty more SQM’s to make Jan’s day !! Strangeness is alive & well • The systematic studies of strangeness production have entered a very sophisticated stage (volume effects, timescales, medium effects) • We have a program that is relevant at high energies (RHIC,LHC) and high densities (new facilities in Europe and Japan).