Search for the onset of baryon anomaly at RHIC-PHENIX

1
Search for the onset of baryon anomaly at
RHIC-PHENIX

• Tatsuya Chujo
• for the PHENIX collaboration

2
Introduction Baryon Anomaly at RHIC
PHENIX PRL 91, 172301 (2003), PRC 69, 034909
(2004)

• In AuAu ?sNN 200 GeV central collisions
• 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).
• Called Baryon anomaly at RHIC.
• Quark recombination models reproduce the data
  qualitatively.

AuAu _at_ ?sNN 200 GeV
Nuclear Modification Factor
RCP
3
p/? ratios in AuAu 200 GeV
More (anti) baryons than pions at moderate pT
(2-5 GeV/c). Does not look like vacuum jet
fragmentation.
PHENIX PRL 91, 172301 (2003), PRC 69, 034909
(2004)
Central
Peripheral
(anti-) Proton /? Ratio

• Where is the onset of the baryon anomaly at RHIC?
• New CuCu data at lower ?sNN may give an
  answer...

4
Data Analysis

• Data set
• RHIC Run-5 (2005), measured by the PHENIX
  experiment.
• CuCu at 22.5 GeV.
• CuCu at 62.4 GeV.
• 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.
  

5
Results

1. pT spectra in CuCu at ?sNN 22.5 and 62.4 GeV.
2. p/? and ?p/?- ratios vs. pT.
3. Nuclear modification factor RAA.

6
pT spectra for pions
Filled symbols ? Open symbols ?-
7
pT spectra for kaons
Filled symbols K Open symbols K-
8
pT spectra for protons
No weak decay feed-down correction applied
9
pT spectra for antiprotons
No weak decay feed-down correction applied
10
p/? in CuCu 22.5 GeV

• Larger p/? ratios than those in AuAu 200 GeV
  (0.5 _at_ pT 1.5 GeV).
• Affected by the spectator protons (not produced
  protons) at lower ?sNN.
• ?p/?- ratios are 0.3-0.4 at pT 2 GeV/c, which
  is close to the fragmentation expectations in
  pp.
• Almost no centrality dependence.

11
p/? in CuCu 62.4 GeV

• p/? ratios are reduced, compared to those in
  CuCu 22 GeV.
• ?p/?- ratio in most central collisions reaches
  R0.6 at pT 2 GeV/c.
• Centrality dependence is seen.
• Peripheral pbar/?- consistent with pp value.

12
Beam energy dep. in CuCu

• p/? ratio decreasing as a function of ?sNN.
• ?p/?- ratio increasing as a function ?sNN.
• CuCu 22.5 GeV central data reaches the pp
  values.
• CuCu 62.4 GeV central data is higher than that
  in 22.5 GeV.

13
RAA for pions (22 GeV)

• Error notations
• - Error bars statistical error for CuCu spectra
• - Gray boxes
• 1) sys. error for pp reference.
• 2) sys. error for CuCu spectra.
• - Lines Ncoll error (1?.)

• pp reference global fit of pion data at ?s 23
  GeV (D. dEnterria).

• pp reference global fit of pion data at ?s 22
  GeV in pp.
• RAA is 1.5 at pT 2 GeV/c, no suppression.

14
RAA for pions (62 GeV)

• pp reference global fit of pion data at ?s 62
  GeV.
• nucl-ex/ nucl-ex/0411049, D. dEnterria.

• Similar, might be slightly smaller than that in
  22 GeV.

15
RAA for proton (22 GeV)

• pp reference fitted the ISR data in pp 23
  GeV, B. Alper et al, NPB 100, 237 (1975).

• Larger than pions significantly, which suggests
  the large contributions of spectator protons.

16
RAA for proton (62 GeV)

• pp reference fitted the ISR data in pp 63
  GeV, B. Alper et al, NPB 100, 237 (1975).

• Similar as in 22.5 GeV, but slightly smaller
  value.

17
RAA for antiproton (22 GeV)

• pp reference fitted the ISR data in pp 23
  GeV, B. Alper et al, NPB 100, 237 (1975).

• Different pT dependence from protons.
• RAA 1 (similar to pions RAA), binary
  collision scaling worked?

18
RAA for antiproton (62 GeV)

• pp reference fitted the ISR data in pp 63
  GeV, B. Alper et al, NPB 100, 237 (1975).

• Similar to that for 22 GeV (and also pions RAA).

19
Summary

• Measured pT spectra for ??, K?, p, ?p in CuCu
  at ?sNN 22.5 and 62.4 GeV in PHENIX.
• p/? ratio decreasing as a function of ?sNN in
  CuCu.
• Suggests a significant contribution of spectator
  protons (not by the produced protons) in lower
  energies CuCu.
• ?p/?- ratio increasing as a function ?sNN in
  CuCu.
• CuCu 22.5 GeV shows that there is (almost) no
  centrality dependence, and central CuCu already
  reaches to the pp values.
• CuCu 62.4 GeV central data is higher than that
  in 22.5 GeV, centrality dependence is seen.
• RAA depends on particle type.
• ? no suppression at both 22.5 and 62.4 GeV in
  CuCu.
• p enhanced (mostly due to the spectator
  nucleons).
• ?p binary scaling, very similar to pions RAA.
• New reference pp data at 62.4 GeV will be taken
  in June 2006 (2 weeks).

20
(No Transcript)
21
Backup Slides
22
pp fit at ?s 22.5 GeV (pions)
Compilation and fitting by D. dEnterria
23
RAA for ?0 in CuCu 22.5 GeV
PbSc (0-10)
PbGl (0-10)
24
SPS and AGS

• Nucl. Phys. A 757, 184 (2005),
• PHENIX, nucl-ex/0410003

25
NA49 data
p/? (NA49)
?p/?- (NA49)

• NA49 collaboration, nucl-ex/0510054

26
RAA for pions
22.5 GeV
62.4 GeV
27
RAA for kaons
22.5 GeV
62.4 GeV
28
RAA summary (22 GeV)
29
RAA summary (62 GeV)
30
?p/p ratio vs. pT
22.5 GeV
62.4 GeV
31
?-/?, K-/K vs. pT (22.5 GeV)
32
?-/?, K-/K vs. pT (62.4 GeV)
33
pp reference data (with fit)
23 GeV
63 GeV
Kaons and protons Fit results of ISR pp 63 GeV
data. B. Alper et al, NPB100(1975)237. pions
global fits of pp data, e.g. nucl-ex/0411049, D.
dEnterria.