An Update from STAR – Using Strangeness to Probe Collisions

1. An Update from STAR – Using Strangeness to Probe Collisions You are never too old to set another goal or to dream a new dream C.S.Lewis 1898-1963

2. Outline Soft - Bulk of the production - v2 flow - Charged hadrons, L, K - Chemical freeze-out – Strangeness enhancement? - Rescattering – K*,L(1520) - Thermal Freeze-out – X,W,f different behaviour? - Radii – K0s HBT Hard – Early times - Quark vs Gluon production – p/p and L/L - High pt suppression – charged hadron vs K0s vs L p-p - <pt> - Mini jets? Outlook – Look out for at QM2004 - Comparison p-p data – Relative rates - d-Au – Cold vs hot nuclear matter - FTPC - L at high y Strange Particles the Ultimate Probes!

3. STAR Strange Spectra @ 200 GeV preliminary preliminary X STAR Preliminary K0s STAR Preliminary f STAR Preliminary K* L STAR Preliminary W Preliminary K

4. Year 2000, The STAR Detector (Year-by-Year) Time Projection Chamber Silicon Vertex Tracker * FTPCs Endcap Calorimeter Vertex Position Detectors Barrel EM Calorimeter + TOF patch year 2001, year-by-year until 2003, installation in 2003 Magnet Coils TPC Endcap & MWPC ZCal ZCal Central Trigger Barrel RICH * yr.1 SVT ladder

5. 130 GeV Data STAR Preliminary W+W All strange particles seem to increase linearly with h- No step functions, no big surprises

6. Improvements with 200 GeV Data STAR Preliminary L+L 18% extrapolation X+X STAR Preliminary K+ STAR Preliminary Better stats. W and W measurements Much higher reach in pt STAR Preliminary Finer centrality binning

7. B/B Ratios • All data: • mid-rapidity • ratios from raw yields STAR p+p √s = 200 GeV Talk: Anja Billmeier, Fri Similar net baryon densities in all 3 collision data Au+Au STAR preliminary

8. Statistical models As we know beautiful agreement between models and data

9. Centrality Systematics of Chemistry Appears to be a saturation of strangeness

10. Statistical models What about the resonances?!? As we know beautiful agreement between models and data

11. Resonances and Survival Probability  K*  K K* measured lost  K K*   K* K K K measured Kinetic freeze-out Chemical freeze-out • Initial yield established at chemical freeze-out • Decays in fireball mean daughter tracks can rescatter destroying part of signal • Rescattering also causes regeneration which partially compensates • Ratio to “stable” particle reveals information on behaviour and timescale between chemical and kinetic freeze-out time Two effects compete – Dominance depends on decay products and lifetime Need more than one resonance

12. Resonance Ratios STAR Preliminary Au-Au and p-p √s=200GeV L(1520) ->pK (13 fm/c) K* -> Kp ( 4 fm/c) r -> pp (1.3 fm/c) UrQMD:signal loss K*(892) (1520) SPS (17 GeV) [1] 66% 50% RHIC (200GeV) [2] 55% 30% Talks: Patricia Fachini, Ludovic Gaudichet & Haibin Zhang, Sun.

13. Hydro-dynamically motivated fit p b s  R Shape of the mT spectrum depends on particle mass STAR Preliminary solid : used in fit - K- Multiple interactions lead to thermalization -> limiting behaviour ideal hydrodynamic flow 1/mT dN/dmT (a.u.) where E.Schnedermann et al, PRC48 (1993) 2462 r =s(r/R)n mT - m0(GeV) Two Parameters: T and b

14. Thermal freeze-out at 130 GeV  • , (?): Show different thermal freeze-out behaviour:  ,K,P, ,K,P, • , K, P, : Common thermal freeze-out at T~100MeV and <>~0.52c Assume br= bs(r/R) Tfo - (), 1 and 2  contours • Early freeze-out due to smaller cross-section ? • Radial flow developing at early times? STAR Preliminary Talk: Javier Castillo, Mon

15. <pt> vs Centrality p, K, p - <pt> increase with centrality - Heavy mass increase faster All consistent with radial flow Talk: Jinguo Ma, Sun f seems to flow differently – Early freeze-out too?

16. Elliptic Flow and the Hydro limit y x Zhang, Gyulassy, Ko, PL B455 (1999) 45 py px coordinate space • Coordinate space configuration anisotropic (almond shape) however, initial momentum distribution isotropic (spherically symmetric) • Only interactions among constituents generate a pressure gradient, which transforms the initial coordinate space anisotropy into a momentum space anisotropy (no analogy in pp) Momentum space High v2 evidence of early thermalization

17. Strange particle v2 at low pt V2 STAR Preliminary Au-Au 200 GeV 1 • Mass dependence • well described by blastwave model modified to allow for an azimuthal modulation of the second harmonic to the transverse rapidity: • = r0 +racos(2f) and a variation in the azimuthal density: s2. Combined fit to K0s and L gives Tfo ~ 100 MeV r0 ~ 0.66 ra ~ 0.04 s2 ~ 0.04 In good agreement with mt spectra Pt GeV/C Also seen at 130 GeV 2002, Phys. Rev. Lett. (2002) 132301-1 Do X and W agree?

18. K0sK0s Correlations X 10 C2 l = 0.5 0.1 Rinv = 5.8  0.7 STAR Preliminary\ K0s Enough K0s/event to perform HBT measurement Fit to a gaussian M (GeV/C2) Talk: Selemon Bekele, Thurs

19. HBT vs mt Wiedemann and Heinz expect: to drop with 1/mat due to collective flow. (a ~ 0.5) Rinv for K0s does not seem to obey same mt scaling Need more detailed studies before conclusive statement made

20. Kaons 200 GeV Au-Au STAR Preliminary Observing Hadronization Timescale The Premise: • Charge/anti-charge pairs are created close in space-time • Early creation (hadron gas) • Longitudinal expansion and rescattering pulls pairs apart • Loose correlation in rapidity • Late creation (after deconfined phase?) • Pairs only form at hadronization, late in collision • Less rescattering • Less loss of correlation in rapidity • Balance function tries to measure this correlation • Width of balance function then related to time between hadronization and freeze-out

21. Balance Function at 200 GeV STAR Preliminary Smooth transition from p-p to Au-Au K narrower than p (just mass effect?) Talk: Gary Westfall, Fri Narrower widths for more central data: Delayed hadronziation?

22. Particle production is large Small change from 130 to 200 GeV Vanishing anti-baryon/baryon ratio (0.7-0.8) close to net baryon-free but not quite, ~same for 130, 200 and pp Particles ratios suggest chemical equilibrium Tch170 MeV, mb<50 MeV  near lattice phase boundary Resonances appear strongly affected by rescattering in medium Rescattering and regeneration compete System exhibits collective behavior (radial + elliptic flow) strong internal pressure that builds up very early Some particles appear to freeze-out at earlier times The system appears to hadronize late Balance function results Large system at freeze-out K0s appear to break mt scaling Summary of Low pt Observations Need more Au-Au data to get clearer picture Overall picture: system appears to be in equilibrium, but it explodes and hadronizes rapidly

23. Strange Particles at High pt preliminary preliminary Change in shape at higher pt.

24. “Soft” vs “Hard” Physics N-N cross section <Nbin>/sinelp+p If no “effects”: R < 1 in regime of soft physics R = 1 at high-pt where hard scattering dominates “Soft” Physics - Npart: Number of participants number of incoming nucleons (participants) in the overlap region “Hard” Physics - Nbin: Number of binary collisions number of equivalent inelastic nucleon-nucleon collisions Nuclear Modification Factor:

25. Identified Particle Measurements preliminary preliminary A significant difference is seen between the pt dependence of K0S and Λ RAA. For pt from 1.8-3.2 GeV/c in central collisions Λ production approximately follows Nbin scaling. At higher pthowever,a suppression with respect to Nbin scaling is seen for both – “standard” fragmentation? Talk: Hui Long, Thurs Baryon/Meson difference or merely mass?

26. Minimum bias v2 preliminary preliminary Au-Au 200 GeV At high pt Hydro-like behaviour stops Deviation occurs earlier For K0s than for L Talk: Paul Sorensen, Thurs Again mass or baryon/meson dependence?

27. Interplay of soft and hard processes GLV theory Hydrodynamics plus jet quenching describes general form of v2 pt dependence Moderate pt - pion dominated by quenched pQCD, - baryon production dominated by non pQCD effects (e.g.baryon junctions or hydro) expect qualitative different v2 behaviour for different particle species Does it explain RAA?

28. Recombination vs Fragmentation Lower pt -Recombination dominates High pt - Fragmentation dominates Intermediate pt - Two processes compete Bass et al., nucl-th/0301087 Also S. Voloshin QM2002 Recombination dominates out to higher pt for baryons (3 q) - hadron suppression due to parton energy loss dominates later RAA different for mesons and baryons, What about v2 ?

29. B/B ratio at High Pt Both Ratios fall at High pt L/L Talk: Ben Norman, Thurs Seeing difference in quark vs gluon production mechanisms?

30. Summary of High pt Observations • Strong hadronic suppression • Onset at different times for different species • Azimuthal anisotropy at high pt • Plateau occurs at different times for different species • Suppression of back-to-back hadron pairs • (Not shown here) • large parton energy loss and surface emission? • Need • d-Au • disentangle initial state effects in jet production • (shadowing, Cronin enhancement) •  resolution of jet quenching picture • J/ and open charm: direct signature of deconfinement?

31. <pt> and p-p collisions L K0s STAR Preliminary p-p 200 GeV STAR Preliminary p-p 200 GeV X Power Law fits STAR Preliminary p+p @s = 200 GeV K0s Talk: Richard Witt, Thurs Not flow in p-p so evidence for mini-jets?

32. News from the front - Latest d-Au update STAR running since January √s = 200 GeV already > 40M events taken! K0s L, L X Varying Number of events in each plot, NO PHYSICS!!!! But there will be..

33. High Rapidity Ls? Not only use the FTPC’s for multiplicity at high y Results from ~ 2 M dAu minbias events FTPC west only (d side) STAR preliminary, uncorrected First hint of L signal in d-Au at forward rapidity

34. Physics with the BEMC Et p0 B(arrel)EMC • High-pt trigger • x100 enhancement at 5 GeV • Jet and Quarkonia Trigger • Under commisioning p0 d-Au Poster – Manual Calderon Thorsten Kollegger • dAu run (January 2003) • 60 modules instrumented • (Dh, Df) ~ (1.0, 2p) • 2400 towers

35. The STAR Collaboration more than 450 collaborators, 46 institutions, 9 countries Many here today: Talks: Selemon Bekele – Kaon HBT Anja Billmeier – Strange particle ratios in p-p Javier Castillo – Multi-strange baryons and thermal freeze-out Patricia Fachini – r and f0 production Ludovic Gaudichet – L(1520) production Hui Long – Suppression of high pt strange hadrons Jinguo Ma – f production Ben Norman – Ratios as function pt and centrality Paul Sorensen – K0s and L Azimuthal Anisotropy Gary Westfall – Balance functions Richard Witt – Strange particle spectra in p-p Haibin Zhang – K* production Posters: John Adams – L reconstruction Manuel Calderon de la Barca Sanchez – J/y triggering Magali Estienne – X reconstruction Julien Faivre – Improving reconstruction with LDA methods? Mark Heinz – K0s reconstruction Thorsten Kollegger – Heavy flavour reconstruction Sevil Salur – S* reconstruction Russia: MEPHI - Moscow LPP/LHE JINR - Dubna IHEP - Protvino U.S. Laboratories: Argonne Berkeley Brookhaven U.S. Universities: Arkansas University UC Berkeley UC Davis UC Los Angeles Carnegie Mellon University Creighton University Indiana University Kent State University Michigan State University City College of New York Ohio State University Penn. State University Purdue University Rice University Texas A&M UT Austin Washington University Wayne State University Yale University Brazil: Universidade de Sao Paulo China: IHEP – Beijing IMP - Lanzou IPP – Wuhan USTC SINR – Shanghai Tsinghua University Great Britain: University of Birmingham France: IReS Strasbourg SUBATECH - Nantes Germany: MPI – Munich University of Frankfurt India: IOP - Bhubaneswar VECC - Calcutta Panjab University University of Rajasthan Jammu University IIT - Bombay VECC – Kolcata Poland: Warsaw University of Tech.