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

Quark Matter 2006 (2006.11.18)

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

Tatsuya Chujo

(University of Tsukuba)

for the PHENIX collaboration

2Tatsuya ChujoQuark Matter 2006 (2006.11.18)

OutlineOutline1. Introduction (baryon anomaly at RHIC)2. Data set and analysis3. 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 charge

d pions, protons, antiprotons.4. Conclusions

1. Introduction (baryon anomaly at RHIC)2. Data set and analysis3. 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 charge

d 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.

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 questionsRemaining 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)

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 pT spectra analysis in PHENIXPID charged pT spectra analysis in PHENIX• Detectors:

• Drift Chamber, PC1, BBC and TOF for PID charged analysis.

• Centrality: • Subdivided minimum bias trigge

red events, based on BBC charge (62 GeV), or the number of PC1 hit (22 GeV).

• Corrections: • Geometrical acceptance, in fligh

t decay. • NOTE: No weak decay feed-do

wn correction applied for all plots in this presentation.

• Detectors: • Drift Chamber, PC1, BBC and T

OF 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 fligh

t decay. • NOTE: No weak decay feed-do

wn correction applied for all plots in this presentation.

Charged particle identification by TOF

Charge x Momentum (GeV/c)

1/ Cu+Cu @ 22.5 GeV


pT spectra at low energy Cu+CupT spectra at low energy Cu+Cu

• Antiproton spectra in Cu+Cu 22.5/62.4 GeV. • We also measured pions, protons for both systems.

* No weak decay feed-down correction applied.


pT spectra in p+p 62.4 GeVpT spectra in p+p 62.4 GeV Data from Run-6 (2006)

at RHIC. Provides an important ba

seline 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.

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.



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

p+p 62.4 GeV, set the baseline for HI data.New PHENIX data agrees with ISR data.




Cu+Cu 22.5 GeV, p/ ratio in central agree with p+p.Many protons, mostly from participant nucleons.




Cu+Cu 62.4 GeV, p/ ratio larger than those in p+p and Cu+Cu 22.5 GeV.




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



Cu+Cu vs. Au+AuCu+Cu vs. Au+Au



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




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



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

Peripheral collisions for all systemsConversing to the same line for both p/- and p/+



Centrality dep. of p/ in Cu+Cu 22.5 GeVCentrality dep. of p/ in Cu+Cu 22.5 GeV

• 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.



• 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.

Centrality dep. of p/ in Cu+Cu 62.4 GeVCentrality dep. of p/ in Cu+Cu 62.4 GeV* No weak decay feed-down correction applied.


sNN dep. of p/- ratio (central)sNN dep. of p/- ratio (central)

• Increasing as a function 　 of s.



sNN dep. of p/+ ratio (central)sNN dep. of p/+ ratio (central)

• decreasing 　 as a function of s.



RAA for charged pions (by ISR fit)RAA for charged pions (by ISR fit)

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.)

• 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).



RAA 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.



RAA 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.



ConclusionsConclusions 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 a

t RHIC is in between 22 GeV and 62 GeV.

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 a

t RHIC is in between 22 GeV and 62 GeV.



Backup SlidesBackup Slides


p/ratios in p+p 62.4 GeVp/ratios in p+p 62.4 GeV

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

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