1. Hadron Suppression and Nuclear kT Enhancement Studied with Neutral Pions from p+C, p+Pb, and Pb+Pb Collisions at sNN = 17.3 GeV
Quark Matter November 18, 2006
Klaus Reygers University of Münster Germany for the WA98 collaboration

2. The question is … High-pT-hadron suppression at RHIC
Strong evidence for QGP formation
Characterization of the medium (dNgluon/dy  1500)
What can we say at CERN SPS energies?
Klaus Reygers, Quark Matter 2006

3. Is there Jet Quenching at sNN = 17.3 GeV? We don’t know!
s = 19.4GeV
Parameterization from Blattnig et al: Large uncertainty!
Blattnig et al., Phys. Rev. D 62 (2000)
Parton energy loss dNgluon/dy = 400 – 600
D. d’Enterria, Phys. Lett. B 596 (2004), 32
C. Blume, nucl-ex/
No measured p+p reference at same energy
Nuclear kT enhancement not well understood at sNN ~ 17 GeV
Klaus Reygers, Quark Matter 2006

4. Cronin Enhancement at sNN = 17.3 GeV
Calculation without parton energy loss:
Cronin enhancement:
Slightly larger in A+A than in p+A
Strongly model dependent: Maximum enhancement factors between ~2 and ~4
sNN = 17 GeV
Cronin + shadowing
I. Vitev, M. Gyulassy, PRL 89, ,2002
I. Vitev, M. Gyulassy
Barnaföldi et al., nucl-th/
X.N. Wang, PRC 61, , 2000
Expect to take out effect of Cronin enhancement on RAA to large extent with p+Pb reference
Klaus Reygers, Quark Matter 2006

5. Idea of this Analysis: p+C and p+Pb as Reference for Pb+Pb RAA
Reaction System
Year
Pb+Pb at sNN = 17.3 GeV
1994, 1995, 1996
p+C, p+Pb at sNN = 17.3 GeV
1996
p0 spectra published:
Eur.Phys.J.C23: ,2002
Presented in this talk
p + C: → Replacement for p+p reference (Ncoll  1.7  expect small Cronin enhancement)
p + Pb: → Study nuclear kT enhancement by comparing to p+C
→ Reference for RAA in Pb+Pb: partially removes effect of Cronin enhancement
Klaus Reygers, Quark Matter 2006

6. WA98 Experiment High Energy Photon Trigger (pT,g > ~ 0.7 GeV/c)
Minimum bias
trigger
Klaus Reygers, Quark Matter 2006

7. Calibration and Peak Extraction
p+C
p+C
p0 peak position in GEANT simulation
Same calibration as in Pb+Pb run
Confirmed with comparison to GEANT simulation
p0 peak width in GEANT simulation
Klaus Reygers, Quark Matter 2006

8. p0 Spectra in p+C and p+Pb
p0 in sNN = 17.3 GeV p+A
preliminary
Transition to high-pT photon sample at pT = 1.4 GeV/c
Similar pT reach as in Pb+Pb
Klaus Reygers, Quark Matter 2006

9. Cross Check: Comparison to NA49
Ratio: WA98 / NA49
sNN = 17.3 GeV p+C
preliminary
NA49, hep-ex/
Good agreement with charged pions from NA49
Klaus Reygers, Quark Matter 2006

10. RpPb with p+C Reference
Effect of minimum bias trigger threshold taken into account
preliminary
RpPb consistent with 1 at high pT
Hint of Cronin enhancement
Klaus Reygers, Quark Matter 2006

11. p+C as p+p Reference
NA49, Eur. Phys. J. C 45, 343 (2006)
preliminary
preliminary
No indication of Cronin enhancement in p+C from comparison to NA49 p+p
Agreement with Blattnig parameterization within errors
Klaus Reygers, Quark Matter 2006

12. RAA in central Pb+Pb at sNN = 17.3 GeV
Proton-nucleus reference measured at same energy:
0-12.7% most central Pb+Pb p0
nuclear overlap function
preliminary
p+C reference
0-12.7% most central Pb+Pb
p0 suppression with respect to p+Pb reference in central Pb+Pb (RAA ~ 0.7 for 0 − 12.7%) p0
preliminary
p+Pb reference
Klaus Reygers, Quark Matter 2006

13. RAA in Pb+Pb with p+C Reference: Centrality Dependence
Ncoll,Pb+Pb = 712 ± 71
Ncoll,Pb+Pb = 807 ± 81
Ncoll,Pb+Pb = 569 ± 57
Ncoll,Pb+Pb = 408 ± 41
Ncoll,Pb+Pb = 207 ± 21
preliminary
Ncoll,Pb+Pb = 78 ± 12
p0 RAA ~ 0.4 in 1% most central Pb+Pb collisions (p+C reference)
Klaus Reygers, Quark Matter 2006

14. RAA in Pb+Pb with p+Pb Reference: Centrality Dependence
Ncoll,Pb+Pb = 712 ± 71
Ncoll,Pb+Pb = 807 ± 81
Ncoll,Pb+Pb = 569 ± 57
Ncoll,Pb+Pb = 408 ± 41
Ncoll,Pb+Pb = 207 ± 21
preliminary
Ncoll,Pb+Pb = 78 ± 12
p0 RAA ~ 0.4 in 1% most central Pb+Pb collisions (p+Pb reference)
Klaus Reygers, Quark Matter 2006

15. p0 Suppression in Central Pb+Pb
p0 in Pb+Pb at sNN = 17.3 GeV
preliminary
p0 suppression in Pb+Pb at sNN = 17.3 GeV for Npart > ~300
Klaus Reygers, Quark Matter 2006

16. Summary
p0’s from sNN = 17.3 GeV p+C and p+Pb used as reference for RAA
p0 suppression at high pT in central Pb+Pb
Looking forward to extraction of dN/dygluon
1% most central: Ncoll,Pb+Pb = 807 ± 81
preliminary
Klaus Reygers, Quark Matter 2006

17. Backup slides
Klaus Reygers, Quark Matter 2006

18. Comparison to other RpA’s
Klaus Reygers, Quark Matter 2006

19. Comparison to WA80
Klaus Reygers, Quark Matter 2006

20. Cronin Enhancement in p+A at sNN = 17.3 GeV
Models calculations for p+A at sNN = 17.3 GeV:
Cronin Enhancement:
Up to a factor 2 for A  200
Large differences between models!
Rp+A
pT (GeV/c)
Barnaföldi et al., nucl-th/
Klaus Reygers, Quark Matter 2006