 PID spectra in STAR  Baryon/anti-baryon ratios  Mixed hadron ratios  Statistical models  Chemical fits  Quark coalescence  Sudden hadronization  Dynamical models  Conclusions Rene Bellwied, Wayne State University, for the STAR Collaboration Mixed Hadron Ratios from STAR

Mixed Hadron Ratios in year-1 Particle Identification Methods Topology Analysis (V0’s) dE/dx in TPC (  ,K ,p) Advanced Topology (kinks for K   Mixed event method (resonances, V0’s) Corrected Spectra as a function of Centrality Rapidity Transverse Momentum or Mass June 25, 2000 Rene Bellwied

Geometry Trigger and Multiplicity Cuts Data Summer 2000  2.0 M total trigger events taken, 844 K central (top 15%)  331 K good (top 5%) central for physics analysis  458 K good min bias events for physics analysis 5% Central Reconstructed vertex events n ch - number of primary tracks in |  | < 0.75 ~ 90% of all hadronic Au+Au interactions central collisions 

Particle Identification in TPC and RICH Time Projection Chamber dE/dx below 1 GeV/c Preliminary Ring Imaging Cherenkov Detector Cherenkov angles at higher momenta

T  = 190 MeV T  = 300 MeV T p = 565 MeV mid-rapidity y=  Increase with collision centrality  consistent with Radial Flow Slope Parameters via dE/dx PID

Particle Identification via Topology Decay vertices K s   + +  -   p +  -   p +  +  -   +  -  +  +  +    + K -   “kinks”: K     + VoVo

Slope Parameters via V0 PID (y=  Larger pt-range than dE/dx, better characterization of flow

m t scaling depends on fit range solid : used for fit m T - m [GeV/c 2 ] 1/m T dN/dm T (a.u.)  K p 

STAR B/B Ratios Ratio approaching 1.0 as strangeness content increases Ratios calculated for central events at mid- rapidity, averaged over experimental acceptance in p t STAR preliminary

Energy Evolution of B/B Ratio STAR preliminary Production of baryons through pair processes increases dramati- cally with  s – still not baryon free Pair-process production is larger than baryon transport Note: 2/3 of protons from pair processes, yet pt dist. the same as antiprotons (ISR)

Mid-rapidity values for Central Collisions Comparing RHIC (130 GeV) to SPS K + /K - = 1.08 ±0.01 (stat.)±0.06  /h - = ± (stat.)±0.004 K*/h - = 0.06 ± (stat.)±0.01 K*/h - = ± (stat.)±0.01 p/p = 0.6  0.02 (stat.)  0.06 ¯  /  = 0.73 ± 0.03 (stat.)  = 0.82 ± 0.08 (stat.) ¯ ¯ ¯ Thermal Fit (prel.): T = 175  7 MeV,  B = 50  6 MeV

Statistical models Braun-Munzinger et al. (hep-ph/ ) - Follows curve for / = 1 GeV at freezeout - Uses phenomenological parameterization: J. Cleymans & K. Redlich, PRL 81 (1998) 5284

T and  B according to thermal model Assumption: strangeness in complete equilibrium i.e. strangeness saturation factor  s = 1

Wroblewski factor evolution Wroblewski factor dependent on T and  B dominated by Kaons Peaks at 30 A GeV in AA collisions due to strong  B dependence mesons baryons hidden strangeness mesons PBM et al., hep-ph/ total

Strangeness production Lines of constant S where: / = 1 GeV I. Increase in strange/non-strange particle ratios II. Maximum is reached III. Ratios decrease (Strange baryons affected more strongly than strange mesons) Braun-Munzinger et al. hep-ph/

K/  ratio as a function of beam energy saturation ?

K/  ratio as a function of beam energy

Experimental  4  yields

Strange Baryon production as a f(centrality) Note: spectra are not feed-down corrected  yields are from fits to Boltzmann; h - yields are power law fits STAR Preliminary Conclusion:Strange baryon over charged particle ratio is constant Saturation ?

Statistical model fit at 130 GeV

Chemical fit result Central Chemical freeze-out parameters T ch = 179±4 MeV  B = 51±4 MeV  s = -0.8±2.0 MeV  s = 0.99 ±0.03  2 /dof = 1.5 Ratio (data) Ratio (chemical fit) BRAHMS PHENIX PHOBOS STAR K  /K  // // // p/p K  /h  K  /h  K  s /h  K/K/ K/K/ p/   p/   K  /h   /h   /h    /h    /h  Model: M.Kaneta, Thermal Fest (BNL, Jul 2001), N.Xu and M.Kaneta, nucl-ex/

Implications for ratios (PRELIMINARY) STAR 130 GeV 14% central (    (*0.2) Braun-Munzinger et al. hep-ph/ Statistical errors only Mid-rapidity ratios

Sensitivity to multi-strange baryons Stat. model can’t get a     ratio above 0.09 in this phase space! D. Magestro private communication

Implications for ratios (PRELIMINARY) STAR 130 GeV 14% central (    (PRELIMINARY) STAR 130 GeV 14% central (      (*0.2) Braun-Munzinger et al. hep-ph/ Statistical errors only Mid-rapidity ratios

Sensitivity to multi-strange baryons T (MeV) Ratios Model gets K - /  ,  /  - correct, but misses on  ratios!!! Statistical errors only +/+/ (Preliminary) STAR 130 GeV 14% central data  - /K - Braun-Munzinger et al. hep-ph/ Thermal fit results in T = 174 MeV,  B = 46 MeV. Grand canonical ensemble, unlike previous model

Quark-Counting Ratios (ALCOR model) Predict Measure Biro, Levai, Zimanyi: Phys. Lett. B347 (1995) p6 Assumption: formation of a constituent quark plasma with subsequent coalesence of the quarks into hadrons

Quark-Counting Ratios from STAR data Quark-counting ratios are consistent with each other Measured Predicted Statistical errors only Will change slightly with feeddown corrections (not included here) STAR Preliminary

130 GeV Statistical errors only STAR Preliminary 14% central Quark coalescence for mixed ratios     Quark coalescence (ALCOR) Statistical model Quark coalescence does better with     As  B -> 0, sensitivity of the model to particle/antiparticle ratios is lost. Must look at ratios of dissimilar species to resolve model accuracy.

 /p ratio correction factors  m =       m p m = p+(0.64  m  + )  p (      p+1.01 (    p m /  m = p/(    p/(      p m /  m – 1.01

Sudden hadronization model (1999)  / p QGP Sudden Hadronization Model J. Rafelski in nucl-th/ Model predicts “most (anti)baryons produced will carry strangeness.”

Sudden hadronization model (2001)  / p QGP Sudden Hadronization Model J. Rafelski in hep-ph/ (Preliminary) STAR Data Data errors not small enough to discriminate

Stat. model 200 GeV predictions Becattini et al. PRC 64 (2001) Use parameterization: Predicts  ~0.8 (Preliminary) STAR 130 GeV minbias data (CAUTION! Really for 4  ratios) Statistical errors only

Stat. Model Predictions Revisited Becattini et al. PRC 64 (2001) Use parameterization: (Preliminary) STAR 130 GeV Data (CAUTION! Really for 4  ratios) Pretty close to prediction! (Preliminary) STAR 200 GeV minbias data Statistical errors only

What about other models ? The models that do well with the multi-strange baryon mixed ratios are models that assume a quark phase (ALCOR and Rafelski’s models) It seems that purely hadronic statistical models fail for the description of yield and mixed ratios of multi-strange baryons, which was also the case at SPS A transport model assuming an initial plasma phase is doing well at SPS energies (Bass and Dumitru, nucl-th/ ) and should be tested at RHIC The HIJING model can describe the data at the SPS with a purely hadronic scenario if the following additions are applied: baryon junction stopping and pair production: HIJING-BB general cascade program (GCP) for hadronic rescattering: HIJING-BB + GCP transient fluctuating fields or color ropes: HIJING-BB + GCP + Ropes

Some Conclusions Statistical models do well in describing anti-baryon over baryon ratios, which yields constraints on the thermal freeze-out temperature and the baryo-chemical potential. This also allows us to determine an expansion velocity in a dynamical picture (see Helen’s talk). They also do well in Kaon and  ratios which seem to indicate strangeness saturation, whereas the multistrange ratios still seem to indicate strangeness enhancement. This could still be a QGP signature ! the anti-  /anti-p continues to drop from AGS to SPS to RHIC the baryon/meson ratio seems to increase as a function of pt OFF TO THE OMEGAS !!!