Strangeness Production and Thermal Statistical Model Huan Zhong Huang Department of Physics and Astronomy University of California, Los Angeles Department of Engineering Physics Tsinghua University

Strange Particle Discovery 1935 Yukawa: meson exchange model for nuclear interaction Electromagnetic interaction – photons infinite range-- photon massless Nuclear Interaction (Strong Force) – mesons Range (Rutherford Scattering) ~ 1-2 fm Uncertainty principle  E  t ~  c meson mass ~ MeV/c Cloud Chamber  cosmic ray events  mass 106 MeV/c 2 not the Yukawa meson, muon 1947 C. Powell, C. Lattes and G. Occhialini photographic plates at a mountain top m  ~ 140 MeV/c 2    +v

Particle Discovery neutral pion  0   1950 accelerator experiment 1947 G.D. Rochester and C.C. Butler v – decay vertex – discovery V0V0   V+V+  m ~ 1000 m e

Kaon versus pion Pions:       Neutron pions – the anti-particle is itself !! not true to neutral K 0 K 0 and K 0 are different particles ! u, d quark masses 5-10 MeV/c 2 strange quark mass ~ 150 MeV/c 2 SU(3) representation for u,d,s quarks, light quarks

Strangeness Quark Mass Important!

SU(3) Representation of Particles

Strangeness Conservation In Strong Interaction: strange quarks can only be produced in pairs ! Associated Production: p + N  N  K + Pair Production: p + N  pNK + K - Threshold in fixed target: s = (E+m N ) 2 – p 2 Associated Production More Effective (lower low beam energies

Strange Baryons Sensitive to Bulk Partonic Matter T c ~ m s

The Melting of Quarks and Gluons -- Quark-Gluon Plasma -- Matter Compression:Vacuum Heating: High Baryon Density -- low energy heavy ion collisions -- neutron star  quark star High Temperature Vacuum -- high energy heavy ion collisions -- the Big Bang Deconfinement

High Baryon Density at the AGS Si+Si 14.6 A GeV Si+Au 14.6 A GeV Au+Au 11.7 A GeV ARC Yang Pang

Systematic Kaon Measurement NPart NK-NK- NK+NK+ N K +/N K - E802/E859/E866 Au+Au Si+Au

 Measurement ~ 17  s per central AGS

Large  to p Ratio Anti-hyperon absorption in dense medium? Dynamical conversion of anti-protons to anti-Lambda? Similar results from E917. E864/E878

Strangeness is ‘enhanced’ at SPS No of Wounded Nucleons Yield N-wound Baryon and anti-baryons are both enhanced, but by different amount ! WA97/NA57 and NA49 Consistent Results

NPART or No Wounded Nucleons Nucleons wounded once, twice or n times are different ! NA49 Data NPart

Beam-Target Fragmentation Important E910 AGS Strange Baryon Production Increases with Number of Collisions ! NA49 results lead to the same conclusion for p+A collisions ! Both fragmentation and pair production !!

Proton Fragmentation and Hyperon Production data Baryons Very Brittle! pAu  p+X pAu  n+X EQUAL

Energy Dependence of Strangeness Production

Mid-rapidity Ratio versus CM energy

4  Integrated Ratio versus Energy

Strange Quark Production

Quark to Pion Ratio Kink or Not ?

The  to  Many more  s Than  s !!

Scenarios of Baryon Number Transport Direct Transport Through Gluon Junctions …  X) Indirect Transport Through Pair Production Modified by Baryon Chemical Potential …  and  K  and  K  and  p / n ) K Net Baryon Density Increases the Associated Production and Transfers net baryon number to multiply-strange baryons ! Event-by-Event STAR Hyperon Correlations Doable with STAR TOF and SVT Upgrade !

Multi-Strange Baryon Spectrum Shape

Too Many Baryons at Intermediate p T Au+Au 0-10% p+p

Cannot Simply Blame Gluon Fragmentation ! Gluon/Quark ~10-20% difference in baryon production between gluon and quark jets (SLD)

1/3 String Fragmentations Suppress Strange Baryons Standard string fragmentation for baryon formation through diquark tunneling out of string potential: dependence m(ud-1) = 0.49 GeV m(ud-0) = 0.42 GeV predicts  =0.35 . If , STAR data would imply , very unlikely ! RQMD   Diquark fragmentation scheme for multi-strange baryon production in A+A collisions – Ruled Out ?! See M.Bleicher et al, PRL 88, (2002) on  Discussion,

Multi-parton Dynamics and Baryon Production q q q q q q Baryon Anti-Baryon Baryon (Hyperon) Production may be Enhanced by Multi-parton Dynamics: Gluon Junction Mechanism -- (Kharzeev, Gyulassy and Vance ….) Quark Coalescence – (ALCOR-J.Zimanyi et al, AMPT-Lin et al, Molnar+Voloshin …..) Quark Recombination – (R.J. Fries et al….) Key Measurement:  0 /  Ratio  0.35 String Fragmentation  Thermal Statistical  1 Gluon Junction/Coalescence  Physics Implication of multi-parton dynamics on v 2 and R AA Junction

Thermal Statistical Model Particle Density Modified Bessel Function Must Include all particles including resonances !! Physical meaning of  s – phase space suppresion factor

Thermal Statistical Model 62.4 GeV200 GeV T ch (MeV)   B (MeV)  70  20  s (MeV)  GeV

Strangeness Enhancement and  s

Chemical Phase Boundary

Misleadingly Appealing and Beautiful Becattini: T=170,  s =1 PBM (PLB518,(2000)41) predicts y=0 ratios almost exactly K-/K+= exp(2ms/T)(pbar/p)1/3 K- /K+=(pbar/p)1/4 is a fit to the data points Agreement Appealing ! Conceptually ? Equalibrium in local spatial region --- But Measurement in rapidity bin -- Fireball emission region in pT-y. I. Bearden, BRAHMS

Kinetic and Chemical Freezeout

Blast Wave E.Schnedermann et al, PRC48 (1993) 2462 where:  r =  s (r/R) n STAR Preliminary

Blast Wave Fit Parameters: Freeze-out T; Transverse Flow Velocity  T

Different Freeze-out Conditions Multi-strange Baryons freeze-out early: high T and small v Physical origin for non-zero v? // p/K/ 

Have We Observed This ?

Strange Baryon Physics  is special  Quark level clustering or  Sensitive to dynamics of baryon number  v 2 and transverse radial flow reflects partonic collectivity There may be a special di-Omega state  -  ]  2) Baryons, Strange Hyperons, -- Multi-parton Dynamics: Gluon Junctions, Quark Coalescence Quark Recombinations …… We began to investigate quantitatively features which may be related to anisotropy and hadronization properties of bulk partonic matter ! 3) Strange Baryons and Heavy Quarks Are Sensitive Probes of Bulk Properties of Matter at RHIC ! STAR’s future Barrel TOF and MicroVertex detector upgrade will greatly enhance STAR’s physics capability on these topics.

END of Talk

Statistical QCD photon spin electrons spin gluon spin, color quarks spin, color, flavor Energy density reflects the information on what the matter is made of !

Strange Baryons and Dynamics of Early Stages Precision Measurement of  and  Spectra Shape at the Low p T Region is Needed !! Javier Castillo