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					Collision Dynamics at RHIC

         Olga Barannikova
          (Purdue University)
     For the STAR Collaboration
                      Collision Evolution
                  Tc=170 MeV
                eC=0.5 GeV/fm3
  F. Karsch, Nucl. Phys. A698, 199c (2002).

                                                        QCD predicts phase transition
                                                        from hadronic matter to QGP at
                                                        high energy density




                                                                                Elastic scattering
                                                     Hadronic interaction     and kinetic freeze-out
                         QGP and
                                                   and chemical freeze-out
initial state        Hydro. expansion




                                        Hadronization
           pre-equilibrium         Tc                        Tch ?
                                                                                        Tkin ?
  Olga Barannikova                                             Lake Louise Winter Institute, Feb. 2004   2
                   Collision Dynamics
                               Search for final state QGP
                               signals in
                                Bulk properties of the
                                      collision
                               Spectral shapes:
                                   kinetic freeze-out properties
                                  transverse radial flow
                                  Tkin @ kinetic freeze-out
                               Flavor composition:
                                   chemical freeze-out properties
                                   strangeness&baryon production
                                  Tch @ chemical freeze-out


Olga Barannikova               Lake Louise Winter Institute, Feb. 2004   3
              Particle Identification
                          Topological method
                            (p-)                           X +




                                   (X -)



                   dE/dx method




Olga Barannikova                           Lake Louise Winter Institute, Feb. 2004   4
                                       Transverse Mass Spectra
                                                           Spectra shape similar in p+p, different in A+A.
dN/(2π dy pTdpT) [c4/GeV2]




                                                                        pp                                     Au+Au
                                                                                                               central




                                                                                      d2N/(2pmTdmTdy)
                             Variety of hadron species:
                             p , K , K0s, K*, , p, , X, 
                              pp and Au+Au collisions
                             Same experimental setup!
                                                                                                                       mT-m0
                              Olga Barannikova                               Lake Louise Winter Institute, Feb. 2004    5
                            Kinetic Freeze-out
         Blast-wave model:                                          Kinetic freeze-out temperature
E.Schnedermann et al, PRC48 (1993) 2462.

                      m cosh    pT sinh  
             R
  dn
        r dr mT K1  T         I0         
mT dmT 0                 T           T     
   where           tanh -1 r   and       r (r)   s f (r)

                                  Au+Au
                       p-         central
                                                                                  Radial flow velocity
                      K-
                       p                                         – Tkin decreases with centrality

                                                                 – <> increases with centrality


       Olga Barannikova
                                                  p
                                                                   Lake Louise Winter Institute, Feb. 2004   6
                   Particle Production




                               Little centrality dependence
    Increase with centrality      Enhanced strangeness
                               and (anti)baryon production

Olga Barannikova                Lake Louise Winter Institute, Feb. 2004   7
                         Statistical Model Fit
                                     2                                                                Tc
              g i Si             p dp
ni (T ,  )  2  s  ( Ei -  B Bi - s Si ) / T                                                          Tch
             2p      0
                       e                          1




      200 GeV STAR
                                                       –   Tch is insensitive to centrality
                                                       –   Tch ~ Tc: No much interaction from
                                                       hadronization to chemical freeze-out
                                                            What about other particle species?
      Olga Barannikova                                           Lake Louise Winter Institute, Feb. 2004     8
    Kinetic Freeze-out Evolution
                        Sequential kinetic freeze-out: X, ,  
                        , p,K,p,K*
                   Tc
                        , X: Tkin independent of centrality
                               Tkin ~ Tch~ 160 MeV   ~ 0.45c
                                           Initial state broadening?
                                           String fusion? Partonic
                                           flow?

                        Tch ~ 160 MeV,  ~ 0.45, <E > ~ 620 MeV
                                                       rescattering

                         Tkin ~ 90 MeV,  ~ 0.6, <E > ~ 580 MeV

                          Tch  Tkin :         Dt(chkin) ~6 fm/c


                             What about initial state?

Olga Barannikova              Lake Louise Winter Institute, Feb. 2004   9
                        Initial Conditions
                                                             s p r p                   r A 3
                                                                                 2         2       2
                                             (dN / dy )p                                  0
                                                         ,
                                                 s Gluon saturation scale:
                                                                     ( dN / dy)p
                                                        Qs 
                                                                          S

                                          J.P. Blaizot and A.H. Mueller, Nucl. Phys. B289, 847 (1987).
                                          D. Kharzeev and E. Levin, Phys. Lett. B523, 79 (2001).




                                                                   RHIC
                                    Nch
Dynamics at RHIC:
   – different initial conditions
   – same chemical freeze-out condition
   – cooling and expansion with a
   sequential decoupling of particles
     Olga Barannikova                                    Lake Louise Winter Institute, Feb. 2004       10
                       Summary
                   • Initial conditions vary with centrality
                   • Constant Tch ~160 MeV ~ TC
                   • Kinetic freeze-out parameters have centrality
                   dependence: Blast wave model fit (central
                   collisions):
                       - Tkin ,  
                       - sequential kinetic freeze-out: X,, 
                       p,K,p,,K*
                   • Multistrange baryons: Tkin ~ Tch   ch ~ 0.45 c
                   • Tch  Tkin :      Dt(chkin) ~6 fm/c




Olga Barannikova                           Lake Louise Winter Institute, Feb. 2004   11
                   Back-up




Olga Barannikova         Lake Louise Winter Institute, Feb. 2004   12
                  Blast-wave Model Fit
All data were studied within the same framework, Blast Wave model (E.
Schnedermann et. al. PRC48 (1993) 2462). The model assumes a
boosted thermal source in transverse and longitudinal directions.

There are three fit parameters: β – the flow velocity, Tkin – the kinetic
freeze out temperature, and n – that describes the shape of the flow
profile.
                                               n
                                         r
                       r (r )   S (r ) 
                  R                      R
                        tanh -1  r
        r               dn
                              R
                                           pT sinh    mT cosh  
            R                 rdrmT I 0 
                                           T          K1 
                                                        T         
                                                                    
                      mT dmT 0                 kin         kin   


   Olga Barannikova                                Lake Louise Winter Institute, Feb. 2004   13
                   Particle Production




                               p/p
                                                                      200 GeV




                               _
                                                                      130 GeV


                                                                     SPS/NA49

                                                              AGS/E866(x50)



                                                     dNp-/dy
    Increase with centrality         (Anti)baryon enhancement


Olga Barannikova                     Lake Louise Winter Institute, Feb. 2004   14
                   Particle Production




                               K-/p
                                                     dNp-/dy
    Increase with centrality           Little centrality dependence
                                      -- different at lower energies!

Olga Barannikova                       Lake Louise Winter Institute, Feb. 2004   15
              Freeze-out Conditions


                                 Central events:
                                 Statistical model fit results:
                                  p,
                                  K, p:
                                       Tch ~ 160 MeV B ~ 20 MeV
                                       s ~ 4 MeV        ~ 0.9
                                 p,K,p, ,X,:
                                       Tch ~ 160 MeV B ~ 24 MeV
                                       s ~ 1 MeV        ~ 1.0




Olga Barannikova           Lake Louise Winter Institute, Feb. 2004   16
    Kinetic Freeze-out Evolution
                                                     p,K,p     fit
                                                     ,X with p,K,p
                                                     ,X fit




        Au+Au @ 130 GeV
                          , X:
                              Less flow and hotter
                          p,K,p:
                              Strong flow but cool


Olga Barannikova             Lake Louise Winter Institute, Feb. 2004   17
                           Collision Dynamics
                QGP

                          Tc ~ 170±10 MeV         Initial state broadening? String
                                                  fusion? Partonic flow?
Hadronization


                                Tch ~ 160 MeV,  ~ 0.45, <E > ~ 620 MeV
 Chemical
 freeze-out
                                                              rescattering

                                    Tkin ~ 90 MeV,  ~ 0.6, <E > ~ 580 MeV
  Kinetic
freeze-out                                  <E> ~ 600 MeV /particle
                                                g                p
                                              g                   p
                                      600 MeV / parton        T~300MeV
                                           37p 2 4
                                        e      T  10 GeV / fm 3
                                            30
       Olga Barannikova                                     Lake Louise Winter Institute, Feb. 2004   18
                          Time Scale

                                 Tch  Tkin
                   For massless particles in equilibrium:

                            Entropy density ~ T3


                           Tkin Rkin  Tch R3
                             3   3       3
                                            ch

                           Tch          Tch  
                           T - 1 Rch   T - 1 RAu
        DR  Rkin - Rch                     
                           kin          kin 
                           DR   Tch     
                      Dt           - 1  6 fm
                            s  Tkin
                               
                                         
                                         
                                                  c


Olga Barannikova                              Lake Louise Winter Institute, Feb. 2004   19

				
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