1 Jet medium interactions Pawan Kumar Netrakanti (For the STAR Collaboration) Purdue University, USA Motivation Parton energy loss Medium response to energetic partons Summary Outline Workshop on Hot & Dense Matter in the RHIC-LHC Era February 21-14, 2008 TIFR
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1 Jet medium interactions Pawan Kumar Netrakanti (For the STAR Collaboration) Purdue University, USA Motivation Parton energy loss Medium response.
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1
Jet medium interactions Pawan Kumar Netrakanti
(For the STAR Collaboration)Purdue University, USA
Motivation Parton energy loss Medium response to energetic partons Summary
Outline
Workshop on Hot & Dense Matter in the RHIC-LHC EraFebruary 21-14, 2008 TIFR
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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
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
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Current observations in STARAway side yield modification
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
How can we understand these features ?
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Do they give answers to …
Mechanism of energy loss in medium -
Few hard interactions or multiple soft interactions ?What is the Path length dependence of energy loss ? - L2 or LWhat 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
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Di-hadron fragmentation function (Away side)
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
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
RMS =i ( i - )2 yi
i yi
RMS
STAR Preliminary
v2{4}
v2{RP}
v2 sys. error
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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
(1-2)/2
(1-2)/2
3 <pT-trig < 4 GeV/c1 < pT-assoc < 2 GeV/c
dAu
Central Au+Au 0-12%
STAR Preliminary
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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)
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Ridge in Heavy Ion Collisions
What does these features reveal about the medium ?Can we get an idea about the energy lost by partons in the medium?
d+Au, 40-100% Au+Au, 0-5%
3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)
d+AuAu+Au
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Features of the Ridge (at QM2006)
Yield at large independent on
STAR Preliminary
STAR Preliminary
J. Putschke (QM06)
Ridge persists up to high pT-trigTRidge ~ Tinclusive < TjetSTAR : J. Putschke, QM2006
Indication of two contributionsJet contribution + contribution arising due to jet
propagating in the medium
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Jet and Ridge : Observations
Near-side jet yield independent of colliding system, Npart
and trigger particle type High pT-trig leads to higher jet yields Supports : Parton fragmentation after parton Eloss in the mediumRidge yield increases with Npart
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Particle Ratios: Jet & Ridge
Ratios in cone smaller than inclusive Ratios in ridge similar to inclusive
Select both associated particles Near Side: || <0.7 Away Side: | - |<0.7
Mixed events to obtain background : (a) Min-bias events with same centrality (b) (primary vertex z) < 1 cm (c) Same magnetic field configuration
Analysis techniques
STAR Preliminary
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3-particle correlation background
Raw Raw Raw signal Raw Bkg Hard-Soft Bkg1 Bkg1
Bkg1 Bkg2
correlated
Soft-Soft
- -
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STAR Preliminary
dAu
AuAu40-80%
AuAu0-12%
2-pa
rtic
le C
orre
latio
n
STAR Preliminary
3-particle correlation (||<0.7)
STAR Preliminary
dAu
AuAu40-80%
AuAu0-12%
3<pTTrig<10 GeV/c
1<pTAsso<3 GeV/c
Shaded : sys. error.
Line :v2 uncer.
STAR Preliminary
dAu
AuAu40-80%
AuAu0-12%
STAR Preliminary
dAu
AuAu40-80%
AuAu0-12%
0.7<R<1.4
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Comparison (Projections)3<pT
Trig<10 GeV/c 1<pT
Asso<3 GeV/c|| <0.7
AuAu 0-12% is higher than dAu and AuAu 40-80%
0.7<R<1.4
STAR Preliminary
STAR Preliminary
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Summarizing … 3-particle correlation in
Ridge is uniform event by event.
3<pTTrig<10 GeV/c,
1<pTAsso<3 GeV/c, ||<0.7
The ridge is approximately uniform or broadly falling with . No significant structures along diagonals or axes.
STAR PreliminarySTAR Preliminary STAR Preliminary
dAu AuAu 40-80% AuAu 0-12%
+ = Jet
Ridge
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Potential for away-side analysis
3<pTTrig<10 GeV/c
1<pTAsso<3 GeV/c
|-| <0.7
Study the ridge with the help ofDi-hardon correlation w.r.t. reactionplane.
Another tool to study Ridge
STAR Preliminary
3<pTtrig<4GeV/c
1.0<pTasso<1.5GeV/c
STAR Preliminary
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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 Particle ratios in ridge similar to inclusive measurements Di-hadron correlations with respect to reaction plane
indicates - ridge is dominated in-plane, consistent with
medium density effect
STAR Preliminary
Jet Cone vs. Bulk
Ridge vs. Bulk
STAR Preliminary
STAR Preliminary
STAR Preliminary
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Summary: Meduim Response
Three-particle correlation in - can potentially identify the underlying physics of the ridge.
Correlation peak at =~0, characteristic of jet fragmentation, is observed in d+Au, Au+Au 40-80% and central Au+Au 0-12%.
The peak sits atop of pedestal in central Au+Au. This pedestal, composed of particle pairs in the ridge, is approximately uniform or broadly falling with in the measured acceptance. No significant structures along diagonals or axes.
Significant step forward in experimental study. Quantitative theoretical calculations are needed for further understanding.
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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