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					Mid-Rapidity Hadron Production Studied with the
          PHENIX detector at RHIC

               Joakim Nystrand
             Universitetet i Bergen
          for the PHENIX Collaboration
                    What is PHENIX?
     PHENIX = Pioneering High Energy
     Nuclear Interaction eXperiment
     A large, multi-purpose nuclear physics
     experiment at the Relativistic Heavy-Ion
     Collider (RHIC)




PT03, Copenhagen 9-10            Joakim Nystrand, Universitetet i
                        The PHENIX collaboration




   A world-wide collaboration of  500 physicists from 51 Institutions
   in 12 countries
PT03, Copenhagen 9-10                      Joakim Nystrand, Universitetet i
                            The PHENIX detector
2 Central
Tracking arms



2 Muon arms



Beam-beam
counters


Zero-degree
calorimeters
(not seen)




    PT03, Copenhagen 9-10              Joakim Nystrand, Universitetet i
Charged particle tracking:
• Drift chamber
• Pad chambers (MWPC)

Particle ID:
• Time-of-flight (hadrons)
• Ring Imaging Cherenkov
(electrons)
• EMCal (, 0)
• Time Expansion Chamber

Acceptance:
|| < 0.35 – mid-rapidity
  = 2  90

    PT03, Copenhagen 9-10    Joakim Nystrand, Universitetet i
Example of a central Au+Au event at snn =200 GeV




PT03, Copenhagen 9-10          Joakim Nystrand, Universitetet i
                  Centrality Definition
                                   Centrality 
                                   impact parameter
                                  Two measures:

                                  Np : Number of
                                  participating
                                  nucleons

                                  Ncoll : Number of
                                  binary (nucleon-
                                  nucleon) collisions




PT03, Copenhagen 9-10            Joakim Nystrand, Universitetet i
                            Centrality Determinartion




For each centrality bin, <Np> and <Ncoll> are calculated from a
Glauber model.
Centrality        <Ncoll>      <Np>
 0 – 10%          95594       3253
10 – 20%          60359       2355
20 – 30%          37440       1675
   •                 •           •
   •                 •           •
 PT03, Copenhagen 9-10                   Joakim Nystrand, Universitetet i
                        Multiplicity
   How many particles are produced (at
   mid-rapidity)?
   How does the multiplicity scale with
   centrality, Np or Ncoll?

 Experimental Method                                         B=0
• Combine the hits in PC1 and PC3.

• The result is a sum of true
combinations (from real tracks) and
combinatorial background.

• Determine the combinatorial
background by event mixing

    PT03, Copenhagen 9-10             Joakim Nystrand, Universitetet i
                     Multiplicity per 2 participants
                                                            HIJING
                                                            X.N.Wang and M.Gyulassy,
                                                            PRL 86, 3498 (2001)
                                                            EKRT
                                                            K.J.Eskola et al,
                                                            Nucl Phys. B570, 379 and
                                                            Phys.Lett. B 497, 39 (2001)




K. Adcox et al. (PHENIX Collaboration), Phys. Rev. Lett. 86(2001)3500

Au+Au at s=130 GeV


     PT03, Copenhagen 9-10                           Joakim Nystrand, Universitetet i
                        Multiplicity at s=200 GeV
   130 GeV                        200 GeV        HIJING
                                                 X.N.Wang and M.Gyulassy,
             PHENIX preliminary                  PRL 86, 3498 (2001)
                                                 Mini-jet
                                                 S.Li and X.W.Wang
                                                 Phys.Lett.B527:85-91 (2002)
                                                 EKRT
                                                 K.J.Eskola et al,
                                                 Nucl Phys. B570, 379 and
                                                 Phys.Lett. B 497, 39 (2001)
                                                 KLN
                                                 D.Kharzeev and M. Nardi,
                                                 Phys.Lett. B503, 121 (2001)
                                                 D.Kharzeev and E.Levin,
                                                 Phys.Lett. B523, 79 (2001)




PT03, Copenhagen 9-10                       Joakim Nystrand, Universitetet i
                 Multiplicity ratio (200/130) GeV
            200GeV/130GeV
               PHENIX preliminary




Stronger increase in Hijing than in data
for central collisions

PT03, Copenhagen 9-10               Joakim Nystrand, Universitetet i
                           Variation with snn




To guide the
eye
   1 dNch
            A  B ln( s)
0.5 N p dy

   PT03, Copenhagen 9-10           Joakim Nystrand, Universitetet i
       0 Identification with EmCal




                            Original spectrum

                        Background subtracted


PT03, Copenhagen 9-10            Joakim Nystrand, Universitetet i
                       Suppressed 0 yield at high pT

                                       A remarkable observation:

                                       Yield above pT  2 GeV/c
                                       scales with Ncoll in peri-
                                       pheral collisions but is
                                       suppressed in central
                                       collisions!
                                       A possible indication of
                                       ”jet-quenching”
                                       Bjorken (1982), Gyulassy &
                                       Wang (PRL(1992)1480), HIJING
K. Adcox et al. (PHENIX Collaboration) Phys. Rev. Lett. 88(2002)022301

   PT03, Copenhagen 9-10                           Joakim Nystrand, Universitetet i
                                           The ratio RAA
                              Quantify the deviation from binary
                              scaling through RAA:
                                              (1 / N EVT )d 2 N  0 / dpT dy
                              RAA ( pT )                         AA
                                            N coll  /  inel  d 2  0 / dpT dy
                                                          pp          pp



Au+Au 200 GeV
S.S. Adler et al. (PHENIX Collaboration)
PRL 91(2003)072301.


p+p 200 GeV
S.S. Adler et al. (PHENIX Collaboration)
hep-ex/0304038, to be published in PRL.




    PT03, Copenhagen 9-10                            Joakim Nystrand, Universitetet i
            Suppression of charged hadrons
  A similar suppression seen also for charged hadrons
  at high pT.




                                 Au+Au 200 GeV
                                 S.S. Adler et al. (PHENIX Collaboration)
                                 nucl-ex/0308006, submitted to PRC.

PT03, Copenhagen 9-10             Joakim Nystrand, Universitetet i
            Intial or Final State Effect?
Suppression at high pT in
AA vs. pp
How about pA (or dA)?

Absence of suppression in
dA suggest that the effect
seen in central AA is due to
the dense matter created in
the collisions.

        d+Au 200 GeV
        S.S. Adler et al. (PHENIX Collaboration)
        PRL 91(2003)072303.

   PT03, Copenhagen 9-10                           Joakim Nystrand, Universitetet i
             Charged-particle Identification
Central arm detectors:
Drift Chamber, Pad Chambers (2 layers), Time-of-Flight.
                          Combining the momentum information
                          (from the deflection in the magnetic
                          field) with the flight-time (from ToF):




  PT03, Copenhagen 9-10             Joakim Nystrand, Universitetet i
The yield is extracted by fitting
the m2 spectrum to a function for
the signal (gaussian) +
background (1/x or e-x)
    PT03, Copenhagen 9-10           Joakim Nystrand, Universitetet i
Correction for acceptance and efficiency  normalized d
and d pT spectrum:




The spectrum has been fit to an exp. function in mT,  exp( -mT/T)

More about the slopes (Teff) later…
   PT03, Copenhagen 9-10                   Joakim Nystrand, Universitetet i
 How are nuclei and anti-nuclei formed in ultra-
 relativistic heavy-ion interactions?

1. Fragmentation of the incoming nuclei.
   Dominating mechanism at low energy and/or at
   large rapidities (fragmentation region). No anti-
   nuclei.
2. Coalescence of nucleons/anti-nucleons.
   Dominating mechanism at mid-rapidity in ultra-
   relativistic collisions. Only mechanism for
   production of anti-nuclei.


  PT03, Copenhagen 9-10          Joakim Nystrand, Universitetet i
                   Coalescence
Imagine a number of neutrons and protons
enclosed in a volume V:
                    A deuteron will be formed when a proton
                    and a neutron are within a certain distance in
                    momentum and configuration space.

                    This leads to:
                                                   2
                          3
                        d Nd       d Np    3

                     Ed       B2  E p      
                           3
                         dpd           dp 3 
                                          p 

                    where pd=2pp and B2 is the coalescence
                    parameter, B2  1/V.
                    Assuming that n and p have similar d3N/dp3
The reality is more complicated…
B2 depends on pT  not a direct measure of the
volume




  Possible explanation: Radial flow.
A. Polleri, J.P. Bondorf, I.N. Mishustin:
”Effects of collective expansion on light cluster spectra in
relativistic heavy ion collisions” Phys. Lett. B 419(1998)19.

                                      Introducing collective
                                      transverse flow
                                      generally leads to an
                                      increase in B2 with pT.

                                      The detailed variation
                                      depends on the choice
                                      of nucleon density and
                                      flow profile.


   PT03, Copenhagen 9-10             Joakim Nystrand, Universitetet i
For the special case
          rT                                rT2
 vd  v f   eT              nT (rT )  exp(  2 )
          R                                  2
           0
Linear flow profile + Gaussian density distribution
 Teff independent of fragment mass,
 Teff(d) = Teff(p)
                                   * mid-central collisions, 40-50% centrality.
Experimentally,
d     Teff = 51526 MeV p             Teff = 3266 MeV*

d         Teff = 48826 MeV           p        Teff = 3316 MeV*
 The gaussian parameterization + linear flow profile give
too little weight to the outer parts of the fireball, where the
flow is strongest.
    PT03, Copenhagen 9-10                   Joakim Nystrand, Universitetet i
                           Conclusions
  A lot of new exciting data (only a fraction was
  shown in this talk)
• Nearly logarithmic increase in multiplicity per
participant with s AGS  SPS  RHIC
•  yield suppressed at high pT in central Au+Au
collisions.
•  yield not suppressed in d+Au collisions 
Suppression in central Au+Au collisions is a final state
effect, caused by the dense medium.
• deuteron/anti-deuteron spectra at mid-rapidity probes
the late stages of relativistic heavy ion collisions.
   PT03, Copenhagen 9-10             Joakim Nystrand, Universitetet i

				
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