Scaling Properties of Identified Hadron

1
Scaling Properties of Identified Hadron
Transverse Momentum Spectra in AuAu and CuCu
Collisions at RHIC-PHENIX
Masahiro Konno for the PHENIX Collaboration
(University of Tsukuba)
2
Hadron production in heavy ion collisions at RHIC

• - Hadron production mechanisms
• Thermal emission
• Quark recombination
• Jet fragmentation
• Bulk properties of the system
• Thermalization
• Collective flow
• Freeze-out (Chemical, Kinetic)
• High-pT phenomena in the medium
• Jet quenching(Energy loss)
• Particle correlation of jets

Soft
Space-time evolution of a heavy ion collision
Hard

• Single particle spectra and particle ratios
  provide the most basic observables to
  investigate the mechanisms of hadron production.
• - Particle Identification (PID) over wide pT
  range is also crucial.

3
Hadron production at intermediate pT

• Baryon/meson difference at intermediate pT (25
  GeV/c)
• Baryon enhancement in particle ratios
• Splitting of v2 strength into baryon/meson
  groups
• - Now explained in quark recombination picture
• - A transition from soft to hard production at
  intermediate pT

p/?
What is the next?
Purposes

• Relative contributions of
• hadron production mechanisms (soft/hard)
• Scaling properties of identified hadron
• pT spectra in different collision systems.

nucl-ex/0608033

• Systematic scan over different collision
• systems (colliding species, beam energies)
• with available data obtained at PHENIX.

v2
PHENIX preliminary
(AuAu, CuCu at vsNN 62.4, 200 GeV)
(mT-m)
4
PHENIX Detector
EM Calorimeter (PID)
TOF (PID)

• - Central Arm Detectors
• Centrality and Reaction Plane
• determined on an E-by-E basis.
• PID (particle identification) is
• a powerful tool to study hadron
• production.

Aerogel Cherenkov (PID)
Aerogel Cherenkov (ACC)
Time of Flight (TOF)
Drift Chamber (momentum meas.)
p
K
Tracking detectors (PC1,PC2,PC3)
p
Veto for proton ID
5
Blast-wave Model Fit

• - Blast-wave model is a hydrodynamic-inspired
  model.
• - Extracting kinetic freeze-out properties with
  BW model.
• Simultaneous fit to pT spectra (?/K/p) for each
  centrality class.

Ref PRC48(1993)2462
?2 map
( Resonance decay feed-down correction not
applied. Instead, tighter pT fitting range
used. ? 0.6-1.2 GeV/c K 0.4-1.4 GeV/c,
p/pbar 0.6-1.7 GeV/c)
Spectra for heavier particles has a convex shape
due to radial flow.
6
Blast-wave Model Fit - Tfo vs. Npart
Tfo 120 MeV
- Npart scaling of Tfo between AuAu and CuCu -
Almost same Tfo at vsNN 62.4, 200 GeV
7
Blast-wave Model Fit - lt?Tgt vs. Npart
lt?Tgt 0.5
- Npart scaling of lt?Tgt between AuAu and CuCu -
Almost same lt?Tgt at vsNN 62.4, 200 GeV
8
ltpTgt vs. Npart
- ltpTgt ?ltKltp (mass dependence) - Consistent with
radial flow picture
- Npart scaling of ltpTgt between AuAu and CuCu -
Almost same ltpTgt at vsNN 62.4, 200 GeV
9
Estimation of p/? at intermediate pT

• Extrapolate low-pT Blast-wave fit results
• to intermediate pT in order to estimate p/?
  ratio.

No weak decay feed-down correction applied.
(hydro p)/(hydro ?)
(hydro p)/(real ?)

• Hydrodynamic contribution for protons is one
• of the explanations of baryon enhancement.
• - Other contribution is also needed
  Recombination, Jet fragmentation

10
Baryon enhancement - p/? vs. Npart
AuAu vs. CuCu at 62.4 GeV
AuAu vs. CuCu at 200 GeV

• Npart scaling of p/? between AuAu and CuCu at
  same vsNN

11
Baryon enhancement - p/? vs. dET/dy

• No Npart scaling of p/? (pbar/?) in AuAu
  between 62.4 and 200 GeV.
• dET/dy scaling of pbar/? seen. gt Proton
  production (at this pT range)
• at 62.4 GeV is partly from baryon transport,
  not only pair production.
• Nuclear stopping is still large at 62.4 GeV.

12
Statistical Model Fit - ?q vs. Npart
- Npart scaling of ?q between AuAu and CuCu -
Larger ?q at vsNN 62.4 GeV than that at 200 GeV
13
Summary

• Scaling properties of PID pT spectra tested
• with AuAu and CuCu data at vsNN 62.4/200
  GeV.
• Bulk properties (dN/dy, ltpTgt, kinetic and
  chemical freeze-out
• properties) are scaled with Npart (volume) at
  same vsNN.
• p(pbar)/? ratios
• (1) Npart scaling between AuAu and CuCu at
  same sqrt(sNN)
• (2) dET/dy scaling between 62.4 and 200 GeV in
  AuAu
• (3) pbar/? is a good indicator of baryon
  enhancement
• MRPC-type TOF counter (?TOF100ps) was
• installed behind the Aerogel for high-pT PID
• upgrade. Run-7 has just started for 200 GeV
• AuAu. Higher-pT physics can be reached.

On-going
14
Backup
15
Statistical Model Fit

• Extracting chemical freeze-out properties with
  statistical model fit.
• Fitting particle ratios of dN/dy (?/K/p) at y0.
• Assuming chemical equilibrium of light quarks
  (u,d,s), ?s1.
• Partial feed-down correction taken into account.

Refs Phys. Rev. C71 054901, 2005
nucl-th/0405068 NPA698(2002)306C

• - Tch, ?q relatively stable
• ?s, ?s not determined with this set of ratios
  (?/K/p). Strangeness info is short.

vsNN 62.4 GeV
16
Statistical Model Fit - Tch vs. Npart
If ?s is free, Tch 155 /- 7 MeV
- Npart scaling of Tch between AuAu and CuCu -
Almost same Tch at vsNN 62.4, 200 GeV