What do we learn from the energy dependence of 2- and 3 particle correlations? ? results from SPS (CERES, NA49)

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What do we learn from the energy dependence of 2-
and 3 particle correlations?? results from SPS
(CERES, NA49)
Harald Appelshäuser (CERES collaboration) Institu
t für Kernphysik Goethe Universität Frankfurt
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jets at SPS

• hard processes are rare at SPS
• there is no pp reference
• qualitative differences and/or
• similarities can shed light on
• jet quenching mechanisms at RHIC
• is there an onset of such mechanisms?

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jets at SPS

• e.g. 3 GeV jet at vsNN17,3 GeV ? ltxgt 0.3
  0.4
• jet production dominated by valence quark
  scattering
• net charge conservation imprinted onto jet
  signal
• isospin is an issue (pp is not a good reference)
• dijet-over-jet yield is large at mid-rapidity

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jets at SPS

• can jets be observed at SPS?
• if yes, are there modifications in A-A?
• if yes, what is their origin?
• does it round off the overall picture?

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CERES history
identified pions ptgt1.2 GeV/c, untriggered

• jet-like structures
• at Df0 and Dfp
• peak at Dfp broadens
• in central collisions

CERES PRL92, 032301 (2004) Although the
back-to-back correlation broadens in central
collisions, there is no sign of its suppression.
PRL92,032301 (2004) J. Bielcikova, PhD work
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CERES experiment

• SDD
• Silicon Drift Detector
• RICH
• Ring Imaging Cherenkov
• Counters
• TPC
• Time Projection Chamber
• ? 2.1-2.65 (ymid2.9)
• ? 0-360

data set
3107 Pb-Au events at 158 AGeV/c (vsNN 17.3
GeV)
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di-hadron correlation analysis
pt (2.5-4.0) GeV/c (1.0-2.5) GeV/c
flow
jet
two-source model
elliptic flow in trigger- (A) and associate (B)
pt range determined with CERES
reaction-plane analysis
ZYAM (Zero Yield At Minimum) J(??min) 0
? Subtract flow from C(??) to get jet
correlations
flow subtraction
conditional yield
Jet- associated particles per trigger
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di-hadron correlations
all charge combinations trigger (2.5-4.0)
GeV/c assocs (1.0-2.5) GeV/c
flow contribution (/-stat.
uncertainties in v2)
conditional yield correlation function
Pb-Au 158 AGeV/c
CERES preliminary

• jet-like peak at the near-side
• broad structure at the away-side

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di-hadron correlations
SPS
RHIC
Pb-Au 17.3 GeV 0-5
PHENIX PRL 98 (2007)
CERES preliminary
pt(T) 2.5 4 GeV/c, pt(A) 1.0 -2.5 GeV/c ??
(PHENIX) 0.7, ?? (CERES) 0.5

• relative increase of the away-side yield
• otherwise similar features at SPS and RHIC

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di-hadron correlations
pt(T) 2.5 4 GeV/c, pt(A) 1.0 -2.5 GeV/c ??
(PHENIX) 0.7, ?? (CERES) 0.5

• strong decrease of per-trigger yield at SPS
• stronger trigger bias
• larger contamination of non-jet triggers

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near- and away-side yields
over- lapping pt ranges
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near- and away-side yields
pt(T) 2.5-4.0 GeV/c

• near-side spectrum softer
• due to trigger bias

• qualitatively same behaviour in data
• pt-dependence of away-side yield
• consistent with inclusive distribution

pt(T) 2.5-4.0 GeV/c
CERES Pb-Au 0-5 17.3 GeV Preliminary
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near- and away-side yields

• away-side yield shifted to lower pt?

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charge correlations

• near-side
• higher yield for unlike-sign
• combinations
• charge correlation in the
• fragmentation process
• away-side
• higher yield for positive
• associates
• ?net positive charge

• look at ratios

for a given trigger sample
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charge correlations - PYTHIA
vsNN 17.3 GeV CERES acceptance
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charge correlations - PYTHIA
mid-rapidity
pt(T) 2.5-4.0 GeV/c pt(A) 1.0-2.5 GeV/c
R-
R-
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charge correlations
near-side large difference observed in data
consistent with PYTHIA ? near-side is jetty
CERES Pb-Au 0-5 vsNN17.3 GeV preliminary
-1
0
1
qTrig
away-side data favor bulk composition rather
than jet fragmentation ? away-side is mediumy
qTrig
-1
0
1
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three particle correlations
preliminary CERES results presented at QM2006
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three particle correlations
flow
Two-particle correlation
measured!
Three-particle correlations
J. G. Ulery and F. Wang, NIM A595 (2008)
1. jet-jet
2. hardsoft
3. soft-soft (mixed events) flow trigger

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three particle correlations
Stefan Kniege PhD Frankfurt
soft-soft trigger flow
raw hard-soft
CERES has no sensitivity to 3-p-correlations
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three particle correlations
Stefan Kniege PhD Frankfurt
systematic errors assume 10 smaller v2
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?? correlations
Stefan Kniege PhD Frankfurt
?? gt p - 1.0
?? lt 1.0
pt(A) 0 - 0.5 GeV/c
pt(A) 0 - 0.5 GeV/c
CERES Pb-Au preliminary
CERES Pb-Au preliminary

• away-side structureless

• evolution of peak with trigger pt
• ridge unclear (? NA49)

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??-?f correlations
pt(A) 0-0.5 GeV/c
pt(A) 1-1.5 GeV/c
pt(A) 0.5-1 GeV/c
??
CERES Pb-Au preliminary
pt(T) 3-4.5 GeV/c
pt(T) 2.5-4 GeV/c
pt(T) 2-3.5 GeV/c
pt(T) 1.5-3 GeV/c
pt(T) 1-2.5 GeV/c
?f
Stefan Kniege PhD Frankfurt
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NA49 results
Marek Szuba, PhD Warsow (2009) HQ 2008
Excellent agreement with CERES results
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NA49 results
correlation function C2(?f)
Marek Szuba, PhD Warsow (2009) HQ 2008

• smooth evolution of
• near and away-side
• near-side correlation vanishes
• away-side plateau increases
• away-side plateau affected
• by momentum conservation?

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summary

• evidence for jet-like correlations at SPS
• the away-side is modified
• the away-side reflects properties of the medium
• valuable data to study the systematics of jet
  quenching