A Strange Perspective – Spectra

1. A Strange Perspective – Spectra If we knew what we were doing it would not be called research, would it? - A. Einstein

2. Spectra – What to look at mt spectral shapes • Is there evidence of re-scattering? • Enough to thermalise? • If so for all centralities? • Do particles freeze-out at the same temperature? • Is there any dependence on centrality? • How long does rescattering phase last? • What about simpler systems? Shape change as function of centrality Species shape dependence Short lived resonances Compare to p+p

3. Particle identification a) dE/dx c) Topology  K p d e b) Resonances Approx. 10% of a central event

4. Data Quality 1: Resonances STAR Preliminary K* f _ K* Mass and width are consistent with PDG book convoluted with TPC resolution

5. Data Quality 2: Peaks 6e-4W-/ev , 6e-4~W+/ev _ ~0.84 L/ev, ~ 0.61 L/ev ~0.006 X-/ev, ~0.005 X+/ev _ ~1.6 K0s/ev

6. Data Quality 3: Lifetime check Star Preliminary L Star Preliminary K0s Lifetime : 8.03 ±0.05 (stat)cm PDG Value : 7.89 cm Lifetime : 2.64 ±0.01(stat)cm PDG Value : 2.68 cm Get pt shape of correction factors correct

7. Data quality 4: Kaon Comparison STAR Preliminary 3 different methods with 3 drastically different efficiencies get same Slope and yield

8. Comparison of h- and L,L pT dist. Suggestive that the ratio baryons/mesons > 1 at high pT Consequence of radial flow ? or novel baryon dynamics ? Vitev and Gyulassy nucl-th/0104066 STAR Preliminary

9. Kinetic Freeze-out and Radial Flow 1/mt d2N/dydmt Look at mt = (pt2 + m2 )distribution A thermal distribution gives a linear distribution dN/dmt  mte-(mt/T) mt Slope = 1/T If there is transverse flow Slope = 1/Tmeas ~ 1/(Tfo+ mo<vt>2) Want to look at how energy distributed in system. Look in transverse direction so not confused by longitudinal expansion

10. Mass dependence in p+p? NA44- Phys. Rev. Lett (78) 1997 2080 At lower energy (s=23 GeV) p+p collisions all particle species exhibit same inverse slope Deviation of this behaviour in A+A attributed to flow

11. K0s m Spectra Centrality % T (MeV) 0-5 289 ± 3 ± 17 5-10 291 ± 3 ± 17 10-20 286 ± 5 ± 17 20-35 278 ± 4 ± 17 35-75 269 ± 4 ± 16 Spectra well reproduced by an exponential

12. L mt Spectra Note spectra are not feed-down corrected Fits are e(-mt/T) Centrality % T (MeV) 0-5 342 ± 9 ± 20 5-10 336 ± 9 ± 20 10-20 328 ± 7 ± 20 20-35 331 ± 8 ± 20 35-75 295 ± 7 ± 19 L T=300-350 MeV Spectra slightly better fit by a Boltzmann |y|<0.5 See the same results (within errors) for L

13. Inverse slope for f and X _ 0-14% STARPreliminary

14. Mass dependence of mT slopes STAR Preliminary Indication of strong radial flow at RHIC Situation appears to be more complicated at RHIC than at the SPS Note: inverse slope depends on the measured pT range (dE/dx p < 1 GeV/c) 1/mT dN/dmT (a.u.) Multi-strange baryon seems to have early freeze-out mT-m

15. mT dist. from Hydrodynamic type model b s R 1/mT dN/dmT (a.u.) s Ref. : E.Schnedermann et al, PRC48 (1993) 2462 flow profile selected (r =s (r/Rmax)0.5) p K p

16. Fits to the hydro. model  p K- solid : used for fit - Tth[GeV] Tth[GeV] K- - 1/mT dN/dmT (a.u.) p <r > [c] 0 0.4 <r > [c] 0 0.4 ßr (RHIC) = 0.52c Tfo (RHIC) = 0.13 GeV  mT - m[GeV/c2] STAR Preliminary explosive radial expansion at RHIC  high pressure

17. Tth and <br> systematic <r> [c] Tth [GeV] STAR PHENIX • <r> • saturates around AGS energy • increased at RHIC? • Tth • saturates around AGS energy Picture for central collisions - lots of rescattering and flow

18. mT slopes vs. Centrality Common T at most peripheral collisions?

19. mt in p+p at high s Dumitru, Spieles –Phy. Lett. B 446 1999 Pythia – Confirmed by UA1/5 experiments at 540 GeV shows strong mass dependence NOT flow as Hydro calc. shows. Due to mini jets – create colour strings that are not ONLY longitudinal. Want to look in more detail at 200 GeV More complicated picture at high s – How to disentangle

20. p+p, STAR and Strangeness Data is from ~1/10th of that taken Should get nice spectra

21. How long does rescattering last? 10 100 s GeV From spin counting K*/K = vector mes/mes = V/(V+P) = 0.75 See lower ratio at RHIC than in elementary collisions Due to re-scattering of daughters?

22. K* Slope STAR Preliminary Central events (top 14%) K*0 Statistical error only MT-M0 (GeV/c2) T ~ 400 MeV Similar to that of L and f (same mass) No evidence of a low pt suppression Must be short time scale from chemical freeze-out to thermal OR long lifetime with lots of regeneration.

23. Getting the time scale and temp Can be hot and long lived or cooler and short timescales to get same ratio. G. Torrieri and J. Rafelski, hep-ph/0103149 Measure more than one resonance and can pin down T and t

24. What to look at - Conclusion mt suggest thermalization has occurred • Is there evidence of re-scattering? • Enough to thermalise? • If so for all centralities? • Do particles freeze-out at the same temperature? • Is there any dependence on centrality? • How long does re-scattering phase last? • What about simpler systems? Yes but with a large flow. Not seen as strongly by strange particles Flow decreases with decreasing centrality Elastic re-scattering phase short comparison to p+p data harder at this energy

25. The STAR Collaboration Russia: MEPHI - Moscow LPP/LHE JINR - Dubna IHEP - Protvino U.S. Labs: 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 Paolo China: IHEP - Beijing IPP - Wuhan England: 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 Poland: Warsaw University of Technology