Helen Caines Yale University 18 th Winter Workshop on Nuclear Dynamics – Nassau, Bahamas Jan 2002 A Strange Perspective – Spectra If we knew what we were doing it would not be called research, would it? - A. Einstein

Helen Caines Jan 2002 Spectra – What to look at m t spectral shapes Shape change as function of centrality Species shape dependence 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? Compare to p+p Short lived resonances

Helen Caines Jan 2002 Particle identification Approx. 10% of a central event a) dE/dx c) Topology  Kpd e b) Resonances

Helen Caines Jan 2002 Data Quality 1: Resonances Mass and width are consistent with PDG book convoluted with TPC resolution K* _  STAR Preliminary

Helen Caines Jan 2002 Data Quality 2: Peaks ~0.84  /ev, ~ 0.61  /ev _ _ ~0.006   /ev, ~0.005   /ev ~1.6   s /ev 6e -4   /ev, 6e -4 ~  + /ev

Helen Caines Jan 2002 Data Quality 3: Lifetime check  K0sK0s Lifetime : 8.03 ±0.05 (stat)cm PDG Value : 7.89 cm Lifetime : 2.64 ±0.01(stat)cm PDG Value : 2.68 cm Star Preliminary Get p t shape of correction factors correct

Helen Caines Jan 2002 Data quality 4: Kaon Comparison STAR Preliminary 3 different methods with 3 drastically different efficiencies get same Slope and yield

Helen Caines Jan 2002 Comparison of h - and ,  p T dist. STAR Preliminary Suggestive that the ratio baryons/mesons > 1 at high p T Consequence of radial flow ? or novel baryon dynamics ? Vitev and Gyulassy nucl-th/

Helen Caines Jan 2002 Kinetic Freeze-out and Radial Flow If there is transverse flow Look at m t =  (p t 2 + m 2 ) distribution A thermal distribution gives a linear distribution dN/dm t  m t e -(mt/T) mtmt 1/m t d 2 N/dydm t Slope = 1/T Slope = 1/T meas ~ 1/(T fo + m o 2 ) Want to look at how energy distributed in system. Look in transverse direction so not confused by longitudinal expansion

Helen Caines Jan 2002 Mass dependence in p+p? 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 NA44- Phys. Rev. Lett (78)

Helen Caines Jan 2002 K 0 s m  Spectra Centrality % T (MeV) ± 3 ± ± 3 ± ± 5 ± ± 4 ± ± 4 ± 16 Spectra well reproduced by an exponential

Helen Caines Jan 2002 T= MeV  Note spectra are not feed-down corrected  m t Spectra |y|<0.5 Centrality % T (MeV) ± 9 ± ± 9 ± ± 7 ± ± 8 ± ± 7 ± 19 Fits are e (-mt/T) See the same results (within errors) for  Spectra slightly better fit by a Boltzmann

Helen Caines Jan 2002 Inverse slope for  and  _ STAR Preliminary 0-14%

Helen Caines Jan 2002 Mass dependence of m T slopes 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 p T range (dE/dx p < 1 GeV/c) 1/m T dN/dm T (a.u.) m T -m STAR Preliminary Multi-strange baryon seems to have early freeze-out

Helen Caines Jan 2002 m T dist. from Hydrodynamic type model  R  s Ref. : E.Schnedermann et al, PRC48 (1993) 2462 flow profile selected (  r = s (r/R max ) 0.5 ) 1/m T dN/dm T (a.u.)  K p

Helen Caines Jan 2002 explosive radial expansion at RHIC  high pressure ß r (RHIC) = 0.52c T fo (RHIC) = 0.13 GeV K-K- p  -- [c] T th [GeV] [c] T th [GeV] Fits to the hydro. model m T - m [GeV/c 2 ] 1/m T dN/dm T (a.u.) -- K-K- p  solid : used for fit STAR Preliminary

Helen Caines Jan 2002 T th and systematic –saturates around AGS energy –increased at RHIC? T th –saturates around AGS energy STAR PHENIX T th [GeV] [c] Picture for central collisions - lots of rescattering and flow

Helen Caines Jan 2002 m T slopes vs. Centrality Common T at most peripheral collisions?

Helen Caines Jan 2002 m t in p+p at high  s Dumitru, Spieles –Phy. Lett. B NOT flow as Hydro calc. shows. Pythia – Confirmed by UA1/5 experiments at 540 GeV shows strong mass dependence 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

Helen Caines Jan 2002 p+p, STAR and Strangeness Data is from ~1/10 th of that taken Should get nice spectra

Helen Caines Jan 2002 How long does rescattering last?  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?

Helen Caines Jan 2002 K* Slope STAR Preliminary M T -M 0 (GeV/c 2 ) Statistical error only Central events (top 14%) K* 0 T ~ 400 MeV Similar to that of  and  (same mass) No evidence of a low p t suppression Must be short time scale from chemical freeze-out to thermal OR long lifetime with lots of regeneration.

Helen Caines Jan 2002 Getting the time scale and temp G. Torrieri and J. Rafelski, hep-ph/ Can be hot and long lived or cooler and short timescales to get same ratio. Measure more than one resonance and can pin down T and t

Helen Caines Jan 2002 What to look at - Conclusion m t suggest thermalization has occurred Flow decreases with decreasing centrality Yes but with a large flow. Not seen as strongly by strange particles 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? comparison to p+p data harder at this energy Elastic re-scattering phase short

Helen Caines Jan 2002 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