PowerPoint-Pr

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Two- and three particle azimuthal correlations _at_
SPS energy
Stefan Kniege Johann Wolfgang Goethe Universität
Frankfurt a.M.
For the CERES collaboration
ISMD 04-09.08.2007 Berkeley, USA
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Outline
High-pt correlation measurements _at_ SPS

• ?Motivation for the measurement
• ?Previous correlation measurements at RHIC and
  SPS
• ?High-pt hadron correlations at CERES
  (preliminary)
• ? CERES detector setup
• ? analysis method and results for
• two particle correlations
• ? model studies to estimate
  systematic errors
• ? analysis method and results for
• three particle correlations

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High- pt hadron correlations
Study of the fragmentation pattern of jets
produced in hard parton-parton scatterings in
heavy ion collisions
Possibilities for measuring jet properties

• Full reconstruction of a jet
• drawback large background in AA collisions

• Measuring transverse angular
• correlations with respect to a trigger
• ??? distributions same event /mixed events

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Motivation / earlier measurements
PHENIX
nucl-ex/ 0612019
?Vanishing of the away- side in case of high
trigger/associate pt ?Non Gaussian structure
on the away side
nucl-ex/ 0510060

• centrality and
• pt dependence of the yield/shape on the away side

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Centrality and energy dependence
Motivation / earlier measurements
RHIC
SPS
RHIC
PHENIX nucl-ex/0611019
non Gaussian shape also visible at SPS energies
CERES
CERES Collaboration, G. Agakichev, et al. Phys.
Rev. Lett. 92 (2004) 032301
?Centrality depencence of shape of the away side
( !non triggered correlations of pions with
pt gt 1.2 GeV/c )
Key features also observable at SPS energies !?
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CERES Detector setup and data sets
CERES Detector
Components

• SDD
• Silicon Drift Detector
• RICH
• Ring Imaging Cherenkov
• Counters
• TPC
• Time Projection Chamber
• Acceptance ? (8-15)
• ? (0-360)

Data set

• 3107 Pb-Au events

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2-particle correlations
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Measurement 2 particle correlations
Construction of the correlation function
Investigation of different charge combinations
Measured at different centralities s/sgeom
(0-5), (5-10),(10-20) determined by track
multiplicity
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Measurement 2 particle correlations
Assumption two contributions in the correlation
funcion
flow-like
let-like
elliptic flow in trigger- (A) and associate (B)
pt range determined with CERES
reaction-plane analysis
Removing flow contribution
ZYAM (Zero Yield At Minimum) J(??min) 0
? Subtract flow from C(??) to get Jet
correlations
Conditional yield
Jet- associated particles per trigger
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Results Conditional yield
all charge combinations
pt trigger (2.5-4.0) GeV/c associates
(1.0-2.5) GeV/c
flow contribution (stat. unceratinties
in v2)
Conditional yield Correlation function
Non gaussian shape on the away side for more
central collisions
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Results charge selection

• For all centralities
• Yield on the near side more pronounced for unlike
  sign particles
• ? charge correlation in the fragmentation
  process
• Yield on the away side is higher for like sign
  particles
• ?initial collisions

Raw Correlation
flow contribution
s/sgeom 10 - 20
s/sgeom 5 - 10
s/sgeom 0 - 5
Conditional yield
Charge dependence properties of initial state
and fragmentation process
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Detailed view on charge combinations

Trigger sample dominated by positive triggers
?triggers sample dominated by positive triggers
Away side yield higher for positive
associates ? Initial
state dominated by positives
/ /-
-/ -/-
s/sgeom 0 - 5

• Trigger and associates (initial state)
• dominted by positive paritles

• Near side yield higher for
• unlike sign particles

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Summary of results on two particle correlations

• Trigger and away side yield dominated by positive
  particles
• ? Initial state dominated by
  positive particles
• Near side Higher yield for unlike than for like
  sign pairs
• ? charge correlations in
  fragmentaion process
• Away side Non gaussian shape for central
  collisions
• ? Final state interactions
  with the medium

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Interlude Systematic studies
Current analysis (ZYAM) flow jet
Toy model Two uncorrelated sources
jet-trigger random to reaction plane

• Jet-trigger events
• trigger jet associates
• trigger flow associates
• ? random component

Flow-trigger events trigger and associates
flowing
Input v2trig 0.03 v2asso 0.02
yield/trigger
number of flow associates ltnflowgt ?15
probability for a jet trigger pjet 0.1
nflow gtgt ytrig ? random component pjet
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Interlude Systematic errors
Generate correlation function and apply ZYAM to
extract yield
Signal components
Input and extracted yield
ZYAM
jet events
flow events
Random component leads to overestimated flow
modulatoion in ZYAM ( small v2 ? not visible)
Extracted yield in good agreement to input
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Interlude Systematic errors
Increase of v2 v2trig 0.1 v2asso 0.07
corresponding to
s/sgeom 10 - 20
ZYAM
Signal components
Input and extracted yield
jet events
flow events
Same relative overestimation of v2 has large
impact due to subtraction
Significant difference of the extracted yield ?
Shape and yield
Relative change in v2 pjetv2
? Can pjet this quantity bedetermined?
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Determining jet trigger probability pjet
Comparison of number of jet associates to pairs
of associates
ltn jet-asso.gt / trig.(jet)
ltn jet-asso. pairsgt / trig.(jet)
( poissonian distribution of associates )
Jet associate particles
particle yield/trigger pair yield(projection)/trig
ger
Pairs of jet associates
unknown
known from two/three particle analysis
Possibilily to determine yield per jet ?
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3-particle correlations
Investigating the structure on the away side
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3 particle correlations
Impact of jet topologies on the 2 particle
correlation function
Non gaussian shape on the away side
Event by event deflection of jets
Cone like structure in one event
Trigger pt (2.5-4.0) GeV/c Associate
pt (1.0-2.5) GeV/c
s/sgeom (0-5)
pt (2.5-4.0) GeV/c (1.0-2.5) GeV/c
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Toy Model Cone vs. Event by Event
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Contribution to 3-particle correlations
flow
measured !
Two particle correlation
Three particle correlations
(J. G. Ulery and F. Wang, nucl-ex/0609016)
1. jet-jet
2. hardsoft
3. soft soft (mixed events) flowing
trigger

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Three particle correlation functions
all charge combinations
C3
C3
unlike sign assoc.
like sign assoc.
C3
Preliminary
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Background contributions
correlations function
yield
yield
ZYAM
a.u.
- (...... )
offdiogonal components
preliminary
preliminary
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Charge dependence of Yield
Different charge combinations of associate
particles
Correlation function
charge correlations
all
unlike sign like sign
a.u.
a.u.
a.u.
Yield
preliminary
preliminary
preliminary
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Summary

• Non gaussian shape on the away side of
• 2 particle correlation function

• Shape of the correlation function for different
  charge
• combinations indicate
• charge ordering in the fragmentation process

• Shape of the 3 particle correlations indicate
  cone like structure
• on the away side of the jet

Further investigations are needed to draw final
conclusions
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Thank you for your attention
The CERES collaboration
D. Adamova, G. Agakichiev, D. Antonczyk, A.
Andronic, H. Appelshäuser, V. Belaga, J.
Bielcikova, P. Braun-Munzinger, O. Busch, A.
Castillo, A. Cherlin, S. Damjanovic, T. Dietel,
L. Dietrich, A. Drees, S. Esumi, K. Filimonov, K.
Fomenko, Z. Fraenkel, C. Garabatos, P. Glässel,
G. Hering, J. Holeczek, S. Kniege, V. Kushpil, B.
Lenkeit, W. Ludolphs, A. Maas, A. Marin, J.
Milosevic, A. Milov, D. Miskowiec, R. Ortega,
Yu. Panebrattsev, O. Petchenova, V. Petracek, A.
Pfeiffer, M.Ploskon, S. Radomski, J. Rak,
Ravinovich, P. Rehak, W. Schmitz, J. Schukraft,
H. Sako, S. Shimansky, S. Sedykh, J. Stachel, M.
Sumbera, H. Tilsner, I. Tserruya, G. Tsiledakis,
T. Wienold, B. Windelband, J.P. Wessels, J.P.
Wurm, W. Xie, S. Yurevich, V. Yurevich
NPI ASCR, Rez, Czech Republic GSI Darmstadt,
Germany Frankfurt University, Germany Heidelberg
University, Germany JINR Dubna, Russia Weizmann
Institute, Rehovot, Israel SUNY at Stony Brook,
USA CERN, Switzerland BNL, Upton, USA Münster
University, Germany MPI Heidelberg, Germany
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Backup
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Alternative correlations among the associates
trigger
S trigger and accociates from the same event
B trigger, accociate1, associate2 from
different events
cut on associate Df with respect to trigger
trigger
Orientation of angles with respect to the
trigger ?steeply falling Df distribution
Df triglt-gtassgt 1.0
a.u.
Df (rad)
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Monto Carlo studies of the background
s/sgeom (0.0-5.0)

• Monte Carlo construction of non jet-jet
• contributions to the measured data
• based on the 2 particle conditional yield
• and measured elliptic flow.

C(Df)
data
flowjet flowflow
No trigger separation cut
Preliminary
flowflow
Yield of away side pairs
normalized by steeply falling Df distribution
C(Df)
flow comp. subtracted
Preliminary
Preliminary
Trigger pt (2.5-4.0) GeV/c Associate
pt (1.0-2.5) GeV/c
Indication of cone structure on the away side ?
needs further investigation
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Sructure on the away side also seen with cut
around the trigger region
T
Preliminary
Indication of cone structure on the away side ?
needs further investigation
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Three partile correlations
corr hard soft soft soft
trigger flow yield

all
unlike sign associates
like sign associates
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Misc.
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Determining jet trigger probability pjet
mean number of associates (pairs) per
trigger (jet)
Comparison of number of jet associates to pairs
of associates
Poissonian distribution of associates
Jet associate particles
particle yield/trigger pair yield(projection)/trig
ger
Pairs of jet associates
unknown
known from two/three particle analysis
Possibilily to determine yield per jet ?
Possibilily to determine yield per jet ?
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Jet- Jet yield
raw correlations (all charge combinations)
Subtraction of two particle correlations (
softsoft , hardsoft ) (J. G. Ulery and F. Wang
nucl-ex/0609016)
Preliminary
Yield (Preliminary)
s/sgeom (0.0-5.0)
Trigger pt (2.5-4.0) GeV/c Associate
pt (1.0-2.5) GeV/c
Off-diagonal components remain
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Background contributions
trigger flowing
Backgr.
softsoft
hardsoft
yield
correlations function
- (...... )
clear offdiogonal components