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STAR results on Medium Properties and Response of the Medium to Energetic Partons. Bedanga Mohanty (For the STAR Collaboration) Variable Energy Cyclotron Centre, Kolkata. Outline. Motivation Parton Energy Loss Medium Response to Energetic Partons Summary. Motivation. - PowerPoint PPT Presentation
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1
STAR results on Medium Properties and Response of the Medium to Energetic
PartonsBedanga Mohanty
(For the STAR Collaboration)Variable Energy Cyclotron Centre, Kolkata
Motivation Parton Energy Loss Medium Response to Energetic Partons Summary
Outline
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Motivation
Medium properties Physical phenomenon Experimental probes
Energy density Parton Eloss in the medium High pT particle production, and correlations
Velocity of sound Mach cones 3-particle correlations
Partonic interactions
Mechanism of Eloss
Non-Abelian features of QCD - Color factor effects, path length effects of Eloss
Jet-medium coupling
High pT particle production and correlations, correlations with respect to reaction plane
Collectivity and Thermalization
Partonic collectivity, viscosity and interactions
Azimuthal anisotropy
Medium effect on particle production mechanism
Parton recombination, modified/vacuum fragmentation
Identified particle correlations
Correlations play a significant role in understanding medium properties
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Basic Approach
Look for modification
Is there any modification in heavy ion collisions ?
Calibrated probe
Near side Leading/trigger particle
Away side
near away
Associated particles
Absence ofmedium
STAR : PRL 97 (2006) 252001STAR : PLB 637 (2006) 161
Medium formed in heavy-ion collisions
Jet and high pT particle production in pp understood in pQCD framework
Higher the trigger particle pT more probable it is from a jet and more well defined is the jet axis
STAR Preliminary
New STAR high pT p+p results
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Advantage of Di-hadron Correlations
y (fm)
x (fm)Less surface bias
Single Di-hadron
y (fm)
x (fm)
Limited sensitivity of RAA to P(E,E)T. Renk, PRC 74 (2006) 034906
T. Renk and Eskola,hep-ph/0610059
Di-hadron correlations more robustprobes of initial density ~
H. Zhong et al., PRL 97 (2006) 252001
2IAA
2RAA
fmq 2GeV3.08.2~ˆ ±
5
Current Observations in STARAway side yield modification
What does these features reveal about the medium ?
Parton Eloss
High pT suppression
STAR : PLB 655 (2007) 104STAR : PRL 97 (2006) 152301STAR : PRL 91 (2003) 072304
Reappearance of di-jets
STAR : PRL 97 (2006) 162301
pTlp : 4 - 6 GeV/c
pTasoc : 2 GeV/c - pTlp
Away side shape modification
d+Au
Enhanced correlated yield at large on near side
Medium response
STAR : J. Putschke, QM2006STAR : M. J. Horner, QM2006
2.5 < pT
trig< 4 GeV/c
1< pT
assoc < 2.5 GeV/c
pTtrig=3-6 GeV/c,
2 GeV/c <pTassoc< pT
trig
Au+Au
STAR: PRL 95 (2005) 152301J.G. Ulery, QM 2005
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Do they give answers to …
Mechanism of energy loss in medium -
What is the Path length dependence of energy loss ? - L2 or LDo we see a Color charge dependence of energy loss ?
What is the probability distribution of parton energy loss ?Do partons loose energy continuously or discretely?
Where does the energy from the absorbed jets go or how are they distributed in the medium?
- Shock waves in recoil direction - Coupling of radiation to collective flow
Few hard interactions or multiple soft interactions ?
7
Results on Partonic Eloss
Parton Eloss Reappearance of di-jetsMedium response
Is there a difference in quark and gluon Eloss ? Patricia Fachini (Parallel Talk on 5th Feb), Zhangbu Xu (Plenary Talk on 5th Feb)
Path length effects of parton Eloss : Dihadron Fragmentation functions Oana Catu (Parallel talk on 8th Feb)
Di-hadron correlations with respect to reaction plane Aoqi Feng (Parallel Talk on 5th Feb)
Probability distribution of parton Eloss : -hadron correlations A. Hamed (Parallel Talk on 8th Feb)
Results to be discussed in this talk :
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Is there a difference in q, g Eloss
Color factor effects of the type 9/4 not observed in pion, (anti-)proton ratios and Rcp upto pT ~ 12 GeV/c
STAR : PLB 637 (2006) 161 STAR : PRL 97 (2006) 152301 STAR : PLB 655 (2007) 104
Patricia Fachini, Parallel Talk, 5th February
Baryon & meson NMF
STAR Preliminary
Anti-Baryon to meson ratio
STAR Preliminary
EgEq
~ 9/4
Anti-particle to particle ratio
X.-N. Wang,PRC 70 (2004) 031901
STAR Preliminary
2 L<q>
CE s ^
9
Away-side Di-hadron Fragmentation Function
Oana Catu, Parallel Talk, 8th February
zT=pTassoc/pT
trig
Denser medium in central Au+Au collisions compared to central Cu+Cu zT distributions similar for Au+Au and Cu+Cu for similar Npart
STAR Preliminary
STAR Preliminary
1/N
trig d
N/d
z T
IAA
zT
6< pT trig < 10 GeV
Inconsistent with PQM calculations Modified fragmentation model better
STAR Preliminary
H. Zhong et al., PRL 97 (2006) 252001
C. Loizides, Eur. Phys. J. C 49, 339-345 (2007)
Npart
IAA
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Aoqi Feng, Parallel Talk, 5th February
Di-hadron Correlations w.r.t Reaction Plane
out-of-plane S=90oin-plane S=0 3< pTtrig < 4 GeV/c,
pTasso : 1.0- 1.5 GeV/c
trigger in-plane
trigger out-of-plane
20-60% : away-side : from single-peak (φS =0) to double-peak (φS =90o) Top 5% : double peak show up at a smaller φS
At large φS, little difference between two centrality bins
Observations :
Au+Au 200 GeV
STAR Preliminary
STAR Preliminary
d+Au
20-60%
top 5%
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Path Length Effects
Au+Au 200 GeV
3< pTtrig < 4 GeV/c
1.0 < pTasso < 1.5 GeV/c
in-plane:
similar to dAu in 20-60%.
broader than dAu in top 5%.
Out-of-plane:
not much difference between the two centrality bins.
Away-side features reveal path length effects
Aoqi Feng, Parallel Talk, 5th February
RMS =i ( i - )2 yi
i yi
RMS
STAR Preliminary
v2{4}
v2{RP}
v2 sys. error
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Eloss probability distribution : -hadron correlation
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Provides constraints on Eloss probability distributions Possibly gives full accounting of jet energy loss
T. Renk : PRC 74 (2006) 034906
Jet
Prompt
1st measurement of away-side -h correlations Suppression similar level as inclusives in central collisions Note : Ejet = E
A. Hamed (Parallel Talk on 8th Feb)
X.-N. Wang et alPRL 77(1996)231
13
Results on Medium Response
Parton Eloss Reappearance of di-jetsMedium response
Results to be discussed in this talk : Conical Emission : Final 3-particle results with higher pT trigger, PID correlations
Jason Ulery (Plenary Talk on 8th Feb), Gang Wang (Parallel Talk on 8th Feb), Guoliang Ma (Poster), Jiaxu Zuo (Poster), Quan Wang (Poster)
Ridge in heavy ion collisions : Identified particle correlations, 3-particle correlations Correlations w.r.t RP
Pawan Netrakanti (Plenary Talk on 5th Feb), Aoqi Feng, Parallel Talk, 5th Feb,Christine Nattrass (Parallel Talk on 8th Feb), Jiaxu Zuo (Poster), Cristina Suarez (Poster), Betty Abelev (Poster) , Navneet Kumar (Poster)
14
Two component approach -Correlated to trigger (jets..)- Uncorrelated to trigger (except via anisotropic flow)Bkg normalization 3-particle ZYAM
STAR Preliminary
Conical emission or deflected jets ?
Conical Emission
Mediumaway
near
deflected jets
away
near
Medium
Conical Emission
Experimental evidence of Conical emission
See also Jason Ulery - Plenary Talk on 8th February,
(1-2)/2
(1-2)/2
3 <pT-trig < 4 GeV/c1 < pT-assoc < 2 GeV/c
Gang Wang (Parallel Talk on 8th Feb
e-h correlation
STAR Preliminary
dAu
Central Au+Au 0-12%
STAR Preliminary
15
Mach Cone or Cerenkov Gluons
Mach-cone:
Angle independent of associated pT
Cerenkov gluon radiation:
Decreasing angle with associated pT
Naively the observed cone angle ~ 1.36 radians leads to very small (time averaged) velocity of sound in the medium
STAR Preliminary
Strength and shape of away side structures observed depends on assumed magnitude of flow coefficientsIn cumulant approach: no conclusive evidence for conical emission so farClaude Pruneau : STAR : QM2008(Poster), PRC 74 (2006) 064910
C3
Subtraction of v2v2v4 termsusing on v2 = 0.06
Subtraction of v2v2v4 term using v2 = 0.12
STAR PreliminaryCon
e an
gle
(rad
ians
)
pT (GeV/c)
16
Ridge in Heavy Ion Collisions
What does these features reveal about the medium ?Perhaps tells us how the energy lost by partons are distributed
in the medium
d+Au, 40-100% Au+Au, 0-5%
3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)
d+Au
Au+Au
17
Features of the Ridge (at QM2006)
Yield at large independent on
Indication of two contributionsJet contribution + contribution arising due to jet
Propagating in the medium
What could be the different physics possibilities ?
STAR Preliminary
Ridge persists up to high pT-trigTRidge ~ Tinclusive < Tjet
STAR Preliminary
STAR Preliminary
STAR : J. Putschke, QM2006
18
Different Physics Possibilities
Qualitatively consistent with the features of ridge
Following are the new approaches attempted to disentangle different physics possibilities- 3-particle correlation- Identified particle correlation - Di-hadron correlation with respect to reaction plane- System size dependence
QCD bremsstrahlung radiation boosted by transverse flow S.A.Voloshin, Phys.Lett.B. 632(2007)490E.Shuryak, hep-ph:0706.3531
Broadening of quenched jets in turbulent color fields A.Majumder et.alPhys. Rev. Lett.99(2004)042301
Recombination between thermal and shower partons at intermediate pTR.C. Hwa & C.B. Chiu Phys. Rev. C 72 (2005) 034903
In medium radiation and longitudinal flow pushN.Armesto et.al Phys.Rev.Lett.93(2007) 242301
Momentum Kick ModelC.Y. Wong hep-ph:0712.3282
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Jet and Ridge : Observations
Near-side jet yield independent of colliding system, Npart
and trigger particle type High pT-trigleads to higher jet yields Supports : Parton fragmentation after parton Eloss in the mediumRidge yield increases with Npart
Oana Catu, Parallel Talk, 8th February Christine Nattrass, Parallel Talk, 8th February
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Particle Ratios and v2 : Jet & Ridge
Cristina Suarez - Poster,
Ratios in cone smaller than inclusive Ratios in ridge similar to inclusive
Jet : /K0s ~ 0.5 < inclusive
Ridge : /K0s ~ 1 ~ inclusive
Jiaxu Zuo - Poster
Ridge vs. Inclusive
STAR Preliminary
Jet Cone vs. Inclusive
STAR Preliminary
Jet
ridge
Paul Sorenson - Talk 9th Feb, Navneet K. Pruthi - Poster
v2 modulated background + ridge + jet
inferred v2 of events with ridge pair ~ inclusive inferred v2 of events with jet pair < inclusive
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Ridge : Di-hadron Correlation w.r.t RP
jet
ridge
Observations :
Ridge: decreases with φS. Little ridge at larger φS.
Jet: slightly increases with φS. General agreement with d+AuInterpretation :
Strong near-side jet-medium interaction in reaction plane, generating sizable ridge
Minimal near-side jet-medium interaction perpendicular to reaction plane
Aoqi Feng, Parallel Talk, 5th February
STAR Preliminary
3< pTtrig < 4 GeV/c,
pTasso : 1.0- 1.5 GeV/c
Au+Au 200 GeV
20-60%
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Uniform overall excess of associated particles not due to correlated emission
+ =
Ridge : 3-particle Correlation In-medium radiated
gluons diffused inJets
Pawan K. Netrakanti, Plenary Talk, 5th February
In-medium radiated gluons still collimated
Jet fragmentation anddiffused gluons
dAu : Jets AuAu : 200 GeV
3<pTTrig<10 1<pT
Asso<3 ||<0.7
STAR Preliminary
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Outlook : Di-Jets and Jet Reconstruction
Parton Eloss Reappearance of di-jetsMedium response
Results to be discussed in this talk :
Di-jets triggered correlations - Olga Barannikova, Parallel Talk on 8th February
Multi-hadron cluster triggered correlations Brooke Haag - Poster
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Observation of di-jets
Di-Jets Triggered Correlations
Di-jet trigger
T2
A1
T1
What happens to thesefeatures if we trigger on di-jets ?
T1: pT>5GeV/c
T2: pT>4GeV/c A1: pT>1.5GeV/c
25
Di-Jets Triggered Correlations
Au+Au 12% central
||<0.7
T2A1_T1T1A1_T2
-1-1.5 0 1-0.5 0.5 1.5
1
_d
N_
Ntr
ig d
)
STAR Preliminary
0
No Away-side suppression, No Shape modification, no ridge Olga Barannikova, Parallel Talk, 8th February
200 GeV Au+Au, 12% central
T1: pT>5GeV/c
T2: pT>4GeV/c
A: pT>1.5GeV/c
T2A1_T1
T2A1
-1-2 0 1 2 3 4 5
2
0 1
_d
N_
Ntr
ig d
)
-2
4
STAR Preliminary
12% Central40-60% MB60-80% MB
T2A1_T1
STAR Preliminary
Au+Au
d+Au
-1-2 0 1 2 3 4 5
1
0
1
_d
N_
Ntr
ig d
)
STAR Preliminary
2
3
200 GeV Au+Au & d+Au
1
_d
N_
Ntr
ig d
)
Multi-hadron Cluster Triggered Correlations
RSeed
Secondary Seeds
Associated track
Multi-hadron trigger
Motivation: Explore jet-biases in di-hadron correlations Start developing jet reconstruction
Use cluster energy for trigger:- R = 0.3- p
T,seed > 5 GeV
- pT,sec seed
> 3 GeV
Away-side spectrum
Single-hadron and multi-hadron triggers give similar resultRe-confirms single high pT triggered correlation resultsprobes jet-like correlations
0-12% Au+Au
Add 12-15 GeV trigger
STAR Preliminary
Brooke Haag - Poster
27
Summary : Parton Eloss
Differences (due to color factor) in energy loss between
quarks and gluons not observed in the measured pT range
Dense medium formed in Au+Au collisions compared
to central Cu+Cu collisionsCu+Cu and Au+Au : zT distributions similar for collisions
with similar Npart - feature not consistent with PQM
calculationsPath length effects observed : Broader RMS for away-side
distribution in di-hadron correlations from in-plane to
out-of-plane
1st measurement of away-side suppression
in -h correlation
STAR Preliminary
STAR Preliminary
28
Jet Cone vs. Bulk
Summary : Medium ResponseStrong jet-medium interaction observed.Signals of conical emission observed in central Au+Au
Collisions at 200 GeV in 2-component approach Medium responds through ridge formation. New observations should provide significant constrains on the
mechanism of ridge formation o Particle ratios in ridge similar to inclusive measurementso Di-hadron correlations with respect to reaction plane
indicates - ridge is dominated in-plane, consistent with
medium density effect
o 3-particle correlations : jet fragmentation + an overall uniform
excess of associated particles not due to correlated emission
Ridge vs. Bulk
STAR PreliminarySTAR Preliminary
STAR Preliminary
STAR Preliminary
STAR Preliminary
STAR Preliminary
dAu AuAu
29
ThanksThanks to STAR CollaborationArgonne National Laboratory
Institute of High Energy Physics - BeijingUniversity of BirminghamBrookhaven National LaboratoryUniversity of California, Berkeley University of California - DavisUniversity of California - Los AngelesUniversidade Estadual de CampinasCarnegie Mellon UniversityUniversity of Illinois at Chicago Creighton University Nuclear Physics Inst., Academy of SciencesLaboratory of High Energy Physics - DubnaParticle Physics Laboratory - DubnaInstitute of Physics. BhubaneswarIndian Institute of Technology. MumbaiIndiana University Cyclotron Facility Institut Pluridisciplinaire Hubert CurienUniversity of Jammu Kent State UniversityUniversity of KentuckyInstitute of Modern Physics, LanzhouLawrence Berkeley National Laboratory Massachusetts Institute of TechnologyMax-Planck-Institut fuer PhysicsMichigan State University
Moscow Engineering Physics Institute City College of New YorkNIKHEF and Utrecht UniversityOhio State UniversityPanjab UniversityPennsylvania State University Institute of High Energy Physics - ProtvinoPurdue UniversityPusan National UniversityUniversity of RajasthanRice UniversityInstituto de Fisica da Universidade de Sao PauloUniversity of Science and Technology of China Shanghai Institue of Applied PhysicsSUBATECHTexas A&M UniversityUniversity of Texas - AustinTsinghua UniversityValparaiso University
Variable Energy Cyclotron Centre. Kolkata
Warsaw University of TechnologyUniversity of Washington
Wayne State University
Institute of Particle PhysicsYale University University of Zagreb
30
Color Factors and q,g Eloss
i,j represent fermion field indices and a,b gauge field indices
QCD : For SU(3) : Nc = 3 CA = 3 (gluons), CF = 4/3 (quarks)
SU(3) is the gauge group for QCD
S = 0.119
Eg
Eq~ 9/4
2 L<q>
CE s ^
An opportunity to relate experimental observable (of Eloss) to basic ingredient of QCD - Gauge Group through Color Factors
ALEPH : ZPC 76 (1997) 1OPAL :EJPC 20 (2001) 601