Westfälische Wilhelms-Universität
Münster
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 2006
November 18, 2006
Klaus Reygers
University of Münster
Germany
for the WA98 collaboration
Westfälische Wilhelms-Universität
Münster
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?
2
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
Is there Jet Quenching at sNN = 17.3 GeV?
We don’t know!
RAA =
p+W @ s = 19.4GeV
dN / dpT
A+A
TAA ´ ds / dpT p+p
Parameterization
from Blattnig et al:
Large uncertainty!
Parton energy loss
dNgluon/dy = 400 – 600
Blattnig et al.,
Phys. Rev. D 62 (2000) 094030
D. d’Enterria,
Phys. Lett. B 596 (2004), 32
C. Blume, nucl-ex/0609022
 No measured p+p reference at same energy
 Nuclear kT enhancement not well understood at
sNN ~ 17 GeV
3
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
Cronin Enhancement at sNN = 17.3 GeV
Calculation without parton energy loss:
Cronin enhancement:
sNN = 17 GeV
Cronin + shadowing
 Slightly larger in A+A
than in p+A
 Strongly model
dependent:
Maximum enhancement
factors between ~2 and ~4
I. Vitev, M. Gyulassy,
PRL 89, 252301,2002
I. Vitev, M. Gyulassy
Barnaföldi et al., nucl-th/0307062
X.N. Wang, PRC 61, 064910, 2000
Expect to take out effect of Cronin enhancement on RAA
to large extent with p+Pb reference
4
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
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
p0 spectra published:
p+C, p+Pb
at sNN = 17.3 GeV
1996
Presented in this talk
p + C:
Eur.Phys.J.C23:225-236,2002
→ 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
5
Klaus Reygers, Quark Matter 2006
WA98 Experiment
Westfälische Wilhelms-Universität
Münster
2.1 < h < 3.0
High Energy Photon Trigger
(pT,g > ~ 0.7 GeV/c)
3.5 < h < 5.5
Minimum bias
trigger
p
6
0
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
Calibration and Peak Extraction
p+C
p+C
p0 peak position
in GEANT simulation
p0 peak width
in GEANT simulation
 Same calibration as in
Pb+Pb run
 Confirmed with comparison
to GEANT simulation
7
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
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
8
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
Cross Check: Comparison to NA49
Ratio: WA98 / NA49
sNN = 17.3 GeV p+C
preliminary
NA49, hep-ex/0606028
Good agreement with charged pions from NA49
9
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
RpPb with p+C Reference
p+C reference
RpPb =
N coll
N coll
N coll
p+C
N coll
p+Pb
dN / dpT p+Pb
×
dN / dpT p+C
p+Pb
p+C
= 1.7 ± 0.2
= 4.1 ± 0.4
Effect of minimum bias
trigger threshold taken
into account
preliminary
 RpPb consistent with 1 at high pT
 Hint of Cronin enhancement
10
Klaus Reygers, Quark Matter 2006
p+C as p+p Reference
Westfälische Wilhelms-Universität
Münster
NA49, Eur. Phys. J. C 45, 343 (2006)
preliminary
RpC =
11
dN / dpT
N coll
p+C
preliminary
 No indication of Cronin enhancement
in p+C from comparison to NA49 p+p
p+C
´ dN / dpT
p+p
 Agreement with Blattnig
parameterization within errors
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
RAA in central Pb+Pb at sNN = 17.3 GeV
0-12.7% most central Pb+Pb
p0
p+C reference
Proton-nucleus reference
measured at same energy:
RAA =
preliminary
Tp+B
TA+A
dN / dpT A+A
×
dN / dpT p+B
nuclear overlap function
TX+Y = Ncoll
/s
X+Y
inel
NN
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
p+Pb reference
12
preliminary
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
RAA in Pb+Pb with p+C Reference:
Centrality Dependence
RAA =
preliminary
Tp+C
TA+A
dN / dpT A+A
×
dN / dpT p+C
TA+A = Ncoll
A+A
Tp+C = Ncoll
p+C
/s
inel
NN
/s
inel
NN
N
N
Ncoll,Pb+Pb
N
====
712
569
408
807
207
78±±±71
57
41
12
81
21
coll,Pb+Pb
coll,Pb+Pb
coll,Pb+Pb
p0 RAA ~ 0.4 in 1% most central Pb+Pb collisions
(p+C reference)
13
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
RAA in Pb+Pb with p+Pb Reference:
Centrality Dependence
RAA =
preliminary
Tp+Pb
TA+A
dN / dpT A+A
×
dN / dpT p+Pb
TA+A = Ncoll
A+A
Tp+Pb = Ncoll
p+Pb
/s
/s
inel
NN
inel
NN
N
N
Ncoll,Pb+Pb
==807
712
78
569
408
207±±±±12
81
71
57
41
21
coll,Pb+Pb
coll,Pb+Pb =
p0 RAA ~ 0.4 in 1% most central Pb+Pb collisions
(p+Pb reference)
14
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
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
15
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
Summary
 p0’s from sNN = 17.3 GeV
p+C and p+Pb used as
reference for RAA
1% most central:
Ncoll,Pb+Pb = 807 ± 81
 p0 suppression at high pT
in central Pb+Pb
 Looking forward to
extraction of dN/dygluon
16
preliminary
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
Backup slides
17
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
18
Comparison to other RpA’s
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
19
Comparison to WA80
Klaus Reygers, Quark Matter 2006
Westfälische Wilhelms-Universität
Münster
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
Rp+A
 Large differences
between models!
Barnaföldi et al., nucl-th/0307062
20
pT (GeV/c)
Klaus Reygers, Quark Matter 2006