Hadron Production and Radial Flow in Au Au Collisions at RHIC-PHENIX

1
Hadron Production and Radial Flow in AuAu
Collisions at RHIC-PHENIX
Akio Kiyomichi (RIKEN)for the PHENIX
Collaboration
Lake Louise Winter Institute 2005February 20-26,
2005
2
Space-Time Evolution of System at HI Collisions
initial state

• Bjorkens Space-Time Picture
• Hadrons reflect the bulk property of created
  system and its evolution.
• Tch - Chemical freeze-out inelastic scattering
  stops gt particle abundance determine
• Tfo - Kinetic freeze-out elastic scattering
  stops gt spectra shape determine
• High-pT hadron carry information at the early
  stage of the system.

3
What could we learn by Hadron measurements

• Soft process
• Hydrodynamic Collective Expansion (radial flow)
• Hadron spectra may fit by hydrodynamical model.
• Hard scattering
• High-pT hadron may interact with medium

4
Relativistic Heavy Ion Collider (RHIC)

• New machine at BNL
• First Heavy-ion Collider
• Operational since 2000
• 3.83 km, two rings
• 4 experiments
• Species
• AuAu, dAu, pp, CuCu
• Luminosity
• Au-Au 2 x 1026 cm-2 s-1
• p-p 2 x 1032 cm-2 s-1 (polarized)

Run Year Species ?sGeV ?Ldt 01 2000
AuAu 130 1mb-1 02 2001/2002 AuAu 200
24mb-1 pp 200 0.15pb-1 03
2002/2003 dAu 200 2.74nb-1 pp
200 0.35pb-1 04 2003/2004 AuAu 200
241mb-1 AuAu 62.4 9mb-1 05
2004/2005 CuCu 200
5
Event Selection

• Centrality selection
• Use charge sum of Beam-Beam Counter (BBC) and
  energy deposit of Zero-degree calorimeter (ZDC)
  in minimum bias events.
• Extracted Ncoll ( of binary collisions), Npart
  ( of participants), TAuAu(nuclear overlap
  function) based on Glauber model.

6
Charged Hadron PID
EAST ARM
BBC

• Detectors for hadron measurement.
• DCHPC1TOFBBC
• ?? ?/4, -0.35 lt ? lt 0.35
• Charged Hadron PID by TOF
• 0.2lt ? lt 3.0 GeV/c
• 0.4lt K lt 2.0 GeV/c
• 0.6lt p lt 4.5 GeV/c

CENTRAL MAGNET MUON ARM
DCPC1
TOF
7
pT Spectra, mean pT vs. Npart

• Central
• Low pT slopes increase with particle mass.
• Proton and anti-proton yields equal the pion
  yield at high pT.
• Peripheral
• Mass dependence is less pronounces.
• Similar to pp.

• Increase from peripheral to mid-central, and then
  saturate from mid-central to central for all
  particle species.
• Observed clear mass dependence.
• Indicative radial expansion. (consistent with
  hydro picture)

8
Blast-wave model fit
I0 , K1 modified Bessel function

• Phenomenological hydrodynamical model
• Local thermal equilibrium collective expansion.
• Freeze-out temperature (Tfo) and radial flow
  velocity (?T)
• Include resonance effect.

Blast wave model E. Schnedermann et al., PRC48
2462 (1993)
pp collision
Heavy-ion collision
9
Fitting the pT spectra

• Minimize contribution from hard process
• (mT-m0) lt1GeV
• ? ? pT lt 1.2GeV/c, ? K pT lt 1.4GeV/c,? p
  pT lt 1.7GeV/c
• Simultaneous fit to spectra of ?,K,p
• Tfo 60240MeV , 2MeV each
• ?T 0.000.90, 0.01 each
• More fine mesh in small region
• Tfo 90130MeV , 1MeV each
• ?T 0.700.82, 0.002 each

• PHENIX AuAu 200GeV
• Most central Tfo 108MeV, lt?Tgt 0.57
• Peripheral Tfo 168MeV, lt?Tgt 0.27

10
Centrality dependence of Tfo and lt?Tgt

• Npart dependence of expansion is observed
• _at_central saturate
• _at_peripheral Npart ? 0, Tfo increase, lt?Tgt ? 0

11
Beam energy dependence

• Most central event of AuAu or PbPb.
• Radial flow
• Increases with beam energy
• lt?Tgt0.55 at RHIC
• Temperature
• saturate from AGS,
• 100120MeV

(from fits to ?, K, p spectra)
12
Nuclear Modification Factor RAA , RCP
Qualify the of binary collisions
?

• Total multiplicity Npart scaling
• Low-pT region (pT lt 2GeV/c)
• Jets Ncoll scaling
• High-pT in high energy collision.
• Expected behavior
• From Npart scaling at low-pT to Ncoll scaling at
  high-pT region.

Croning effect
hard
binary collision scaling
participant scaling
soft
13
Central-to-Peripheral Ratio (RCP) vs. pT
Ncoll scaling
Shaded boxes Npart, Ncoll determination
errors.
Npart scaling
Line extend Blast-wave fit

• Depend on particle species
• Stray off the hydrodynamical curve at high-pt.
• Proton,anti-proton No suppression, Ncoll scaling
  
• ???suppression
• Theoretical explanations hydrojet model, quark
  recombination model

14
HydroJet and Recombination
Hirano, Nara (Hydro Jet Model) PRC69,034908(2004
) nucl-th/0307015
Fries, Muller, Nonaka, Bass (Fragmentation/Recombi
nation model) PRC68,044902(2003) nucl-th/0306027

• Qualitative agreement in pion suppression and
  proton non-suppression.
• Both model predict that proton suppress at
  6GeV/c.

15
Conclusion

• Results of identified charged hadron spectra.
• AuAu 200GeV Phys.Rev.C69 034909(2004)
• Hydro-dynamical model fit to the spectra with
  resonance decay effect.
• Npart dependence of expansion is observed
• For the most central
• AuAu 200GeV Tfo 108MeV, lt?Tgt 0.57
• High-pT hadron production
• Observed strong pion suppression at high pT in
  central.
• No suppression for proton.
• There are several theories and discussing.
• High-pT PID upgrade Aerogel MRPC-TOF
• PID beyond 5GeV/c.

16
PHENIX Experiment
17
Spare
18
dAu Collisions RAA vs. RdA
Initial State Effects Only
Initial Final State Effects
PHENIX (dAu) PRL91,072303(2003)

• p0 and charged are largely suppressed in central
  AuAu at high pT.
• No Suppression in dAu, instead small enhancement
  observed !
• d-Au results rule out CGC (initial sate effect)
  as the explanation for high pT suppression of
  hadrons in AuAu central.

19
Baryon Anomaly at RHIC
PHENIX PRL 91, 172301 (2003), PRC 69, 034909
(2004)

• Factor 3 enhancement on both p/? and pbar/?
  ratios in central AuAu compared to peripheral
  AuAu, pp at Intermediate pT.
• Peripheral AuAu at high pT Consistent with
  gluon/quark jet fragmentation and IRS data.

• p, pbar No suppression,
• Ncoll scaling at
• 1.5 GeV - 4.5 GeV
• ?0 Suppression

20
Theory 1 Hydro Jet Model
Hirano, Nara (Hydro Jet Model) PRC69,034908(2004
) nucl-th/0307015

• Explicit 3D Hydrodynamical calculations
  (including QGP in EOS)
• Tuned jet quenching effect to reproduce the
  suppression factor in p0 data.
• Hydrodynamics can describe pT spectra up to 2
  GeV/c.
• Jet contributions from 2 GeV/c.

21
Theory 2 Recombination Model
Fries, Muller, Nonaka, Bass (Fragmentation/Recombi
nation model) PRC68,044902(2003) nucl-th/0306027
Meson
Baryon

• Quarks and anti-quarks recombine into hadrons
  locally at an instant
• q?q ? Meson
• qqq ? Baryon
• Thermal part (quark only) and power law tail
  (quarks and gluons) from pQCD.
• Modification of fragmentation function Di?h(z)
  by energy loss of partons.
• Competition between recombination and
  fragmentations mechanism.
• Quark degrees of freedom play an important role.

22
? meson

• ? meson
• Similar mass as proton.
• Followed the ?0 data points, not protons!

23
Model fit with resonance feed down

• Generate resonances with pT distribution
  determined by each combinations of Tfo, ?T.
• Decay them and obtain pT spectra of ?,K,p.
• Particle abundance calculated with chemical
  parameters
• Tch 177MeV, ?B 29MeV (200GeV), Tch 176MeV,
  ?B 41MeV(130GeV)
• RefP.Braun-Munzinger et al,PLB518(2001)41.
• Merge and create inclusive pT spectra. ? ?2 test

• Resonance
• ?? , K?, p, anti-p
• ?0, ??, ?, ?
• K?, K0, anti-K0, ?
• ?, ??, ?0, ??, ?,anti-

24
?2 contours in parameter space Tfo and ?T

• Upper figure show the ?2 test result of
  simultaneous fitting for most-central spectra.
• Lower figure show ?2 contours for each particles.
• There are strong anti-correlation between Tfo and
  ?T.

0-5most central
25
PHENIX Experiment
Two central arms to measure electron, photon, and
hadrons
Global detectors for trigger and event
characterization
Two forward muon spectrometers