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Excitation functions of baryon anomaly and freeze-out properties at RHIC-PHENIX. Tatsuya Chujo (University of Tsukuba) for the PHENIX collaboration. Outline. 1. Introduction (baryon anomaly at RHIC) 2. Data set and analysis 3. Results (from lower energy RHIC data) p T spectra (Cu+Cu/p+p)

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excitation functions of baryon anomaly and freeze out properties at rhic phenix

Excitation functions of baryon anomaly and freeze-out properties at RHIC-PHENIX

Tatsuya Chujo

(University of Tsukuba)

for the PHENIX collaboration

outline
Outline

1. Introduction (baryon anomaly at RHIC)

2. Data set and analysis

3. Results (from lower energy RHIC data)

  • pT spectra (Cu+Cu/p+p)
  • s dependence of p/ ratios
  • Centrality dependence of p/ ratios
  • Nuclear modification factor (RAA) for charged pions, protons, antiprotons.

4. Conclusions

introduction baryon anomaly at rhic
Introduction ~ Baryon Anomaly at RHIC ~

PHENIX: PRL 91, 172301 (2003), PRC 69, 034909 (2004), PRC 74, 024904 (2006)

  • In Au+Au sNN = 200 GeV central collisions:
  • RCP (or RAA)
    • Pions: Strong suppression of yields above pT ~ 2 GeV/c, due to jet quenching effect.
    • Protons: No suppression for at intermediate pT (2-5 GeV/c).
  • p/ and p/ ratios
    • More (anti) baryons than pions at intermediate pT (2-5 GeV/c).
    • Strong centrality dependence.
  • Called “Baryon anomaly at RHIC”.
  • Quark recombination models reproduce the data qualitatively.
what is the definition of baryon anomaly at rhic
What is the definition of baryon anomaly at RHIC?
  • pT region of interest is the intermediate pT (2.0 - 5.0 GeV/c).
  • p/ (p/) ratios are much larger than the fragmentation expectations (p+p).
    • Strong centrality dependence in heavy ion data.
  • Different nuclear modification factor (RCP or RAA) between pions and (anti)protons.
    • Pions: suppression.
    • (anti)protons: no suppression.
remaining questions
Remaining questions
  • Where is the onset of baryon anomaly at RHIC?
  • How p/ and p/ ratios and RAA evolve as a function of s and colliding system?
  • The following low energy data sets have been taken by the PHENIX experiment recently, and they may give us an answer to questions above.
  • Lower beam energy data in PHENIX.
    • Au+Au 62.4 GeV (2004)
    • Cu+Cu 62.4 GeV (2005)
    • Cu+Cu 22.5 GeV (2005)
    • p+p 62.4 GeV (2006)
pid charged p t spectra analysis in phenix

Charged particle identification by TOF

1/

Cu+Cu @ 22.5 GeV

Charge x Momentum (GeV/c)

PID charged pT spectra analysis in PHENIX
  • Detectors:
    • Drift Chamber, PC1, BBC and TOF for PID charged analysis.
  • Centrality:
    • Subdivided minimum bias triggered events, based on BBC charge (62 GeV), or the number of PC1 hit (22 GeV).
  • Corrections:
    • Geometrical acceptance, in flight decay.
    • NOTE: No weak decay feed-down correction applied for all plots in this presentation.
p t spectra at low energy cu cu
pT spectra at low energy Cu+Cu

* No weak decay feed-down correction applied.

  • Antiproton spectra in Cu+Cu 22.5/62.4 GeV.
  • We also measured pions, protons for both systems.
p t spectra in p p 62 4 gev
pT spectra in p+p 62.4 GeV
  • Data from Run-6 (2006) at RHIC.
  • Provides an important baseline for pT spectra in Au+Au and Cu+Cu at sNN = 62.4 GeV.
  • Presented the invariant yields here.
  • Working on the determination of inelastic cross section and trigger bias in PHENIX experiment for the absolute normalization in pT spectra.

* No weak decay feed-down correction applied.

compilation of p ratios central
Compilation of p/ ratios (central)

* No weak decay feed-down correction applied.

p+p 62.4 GeV, set the baseline for HI data.

New PHENIX data agrees with ISR data.

compilation of p ratios central1
Compilation of p/ ratios (central)

* No weak decay feed-down correction applied.

Cu+Cu 22.5 GeV, p/ ratio in central agree with p+p.

Many protons, mostly from participant nucleons.

compilation of p ratios central2
Compilation of p/ ratios (central)

* No weak decay feed-down correction applied.

Cu+Cu 62.4 GeV, p/ ratio larger than

those in p+p and Cu+Cu 22.5 GeV.

compilation of p ratios central3
Compilation of p/ ratios (central)

* No weak decay feed-down correction applied.

Cu+Cu 200 GeV, similar to those in Cu+Cu 62.4 GeV.

compilation of p ratios central4
Compilation of p/ ratios (central)

* No weak decay feed-down correction applied.

Au+Au 62 GeV, p/- is unchanged, p/+ getting larger.

compilation of p ratios central5
Compilation of p/ ratios (central)

* No weak decay feed-down correction applied.

Au+Au 200 GeV, p/- is enhanced, p/+ is similar to p/-

compilation of p ratios peripheral
Compilation of p/ ratios (peripheral)

* No weak decay feed-down correction applied.

Peripheral collisions for all systems

Conversing to the same line for both p/- and p/+

centrality dep of p in cu cu 22 5 gev
Centrality dep. of p/ in Cu+Cu 22.5 GeV

* No weak decay feed-down correction applied.

  • More protons transported to mid rap. instead of production for Cu+Cu 22GeV.
  • Almost no centrality dependence in p/.
  • p/- ratios are ~0.3-0.4 at pT = 2 GeV/c, which is close to the value in p+p.
centrality dep of p in cu cu 62 4 gev
Centrality dep. of p/ in Cu+Cu 62.4 GeV

* No weak decay feed-down correction applied.

  • p/+ ratios are reduced, compared to those in Cu+Cu 22 GeV.
  • p/- ratio in central collisions reaches R=~0.6 at pT = 2 GeV/c.
  • Centrality dependence is also seen.
s nn dep of p ratio central
sNN dep. of p/- ratio (central)
  • Increasing
  • as a function of s.

* No weak decay feed-down correction applied.

s nn dep of p ratio central1
sNN dep. of p/+ ratio (central)
  • decreasing as a function of s.

* No weak decay feed-down correction applied.

r aa for charged pions by isr fit
RAA for charged pions (by ISR fit)
  • Used ISR fit (nucl-ex/0411049, D. d’Enteria) for p+p parameterization.
  • Using ISR fit: Moderate suppression for Au+Au 62.4 GeV, larger than one for Cu+Cu 62/22 GeV (pT > 2.0 GeV/c).
  • Error notations:
  • - Error bars: statistical error for HI spectra
  • - Boxes:

1) sys. error for p+p reference.

2) sys. error for HI spectra.

- Lines: Ncoll error (1.)

* No weak decay feed-down correction applied.

r aa for antiprotons by isr fit
RAA for antiprotons (by ISR fit)
  • Used ISR data at 63 GeV (Alper. NPB 100, 237) for p+p reference.
  • Similar RAA for all three systems.

* No weak decay feed-down correction applied.

r aa for protons by isr fit
RAA for protons (by ISR fit)
  • Used ISR data at 63 GeV (Alper. NPB 100, 237) for p+p reference.
  • Largest RAA for Cu+Cu 22.5 GeV.
  • RAA for Au+Au 62.4 GeV is smaller than that in Cu+Cu 62.4 GeV.

* No weak decay feed-down correction applied.

conclusions
Conclusions
  • Antiproton is a good probe to study the excitation function of baryon anomaly.
  • Only antiprotons in Cu+Cu 22.5 GeV system is different from others:
      • No centrality dependence in p/ ratio at the intermediate pT.
      • Central 0-10% p/ ratio agrees with the value in p+p collisions.
  • From 62 GeV Cu+Cu/Au+Au data:
    • p/- ratio:
      • Baryon anomaly still exists in central Au+Au “AND” Cu+Cu 62 GeV.
    • RAA (by ISR fit, limited pT < 2.5 ~ 3.0 GeV/c)
      • : moderate suppression in Au+Au 62 GeV, unity for Cu+Cu 62 GeV.
      • p: larger in Cu+Cu than that in Au+Au (baryon transportation).
      • p: small differences between Cu+Cu and Au+Au, close to one.
      • To conclude on RAA, it is important to measure the absolute normalized pT spectra in p+p 62.4 GeV.
  • Summary: Data indicates that an onset of baryon anomaly at RHIC is in between 22 GeV and 62 GeV.
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