STAR results on Medium Properties and Response of the Medium to Energetic Partons

1
STAR results on Medium Properties and Response of
the Medium to Energetic Partons
Bedanga Mohanty (For the STAR Collaboration) Varia
ble Energy Cyclotron Centre, Kolkata
Outline

• Motivation
• Parton Energy Loss
• Medium Response to Energetic Partons
• Summary

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Motivation
Correlations play a significant role in
understanding medium properties
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Basic Approach
Calibrated probe
Look for modification
Medium formed in heavy-ion collisions
Higher the trigger particle pT more probable it
is from a jet and more well defined is the jet
axis
Jet and high pT particle production in pp
understood in pQCD framework
STAR PRL 97 (2006) 252001 STAR PLB 637 (2006)
161
Is there any modification in heavy ion collisions
?
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Advantage of Di-hadron Correlations
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Current Observations in STAR
Away side yield modification
High pT suppression
Parton Eloss
pTlp 4 - 6 GeV/c
STAR PLB 655 (2007) 104 STAR PRL 97 (2006)
152301 STAR PRL 91 (2003) 072304
pTasoc 2 GeV/c - pTlp
What does these features reveal about the medium ?
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Do they give answers to
Few hard interactions or multiple soft
interactions ?
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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Results on Partonic Eloss
Parton Eloss
Medium response
Reappearance of di-jets
Results to be discussed in this talk
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)

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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
Patricia Fachini, Parallel Talk, 5th February
STAR PLB 637 (2006) 161
STAR PRL 97 (2006) 152301
STAR PLB 655 (2007) 104
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Away-side Di-hadron Fragmentation Function
zTpTassoc/pTtrig
1/Ntrig dN/dzT
STAR Preliminary
STAR Preliminary
IAA
zT

• Denser medium in central AuAu
• collisions compared to central CuCu
• zT distributions similar for AuAu
• and CuCu for similar Npart

Oana Catu, Parallel Talk, 8th February
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Di-hadron Correlations w.r.t Reaction Plane
in-plane fS0
3lt pTtrig lt 4 GeV/c, pTasso 1.0- 1.5 GeV/c
out-of-plane fS90o
STAR Preliminary
20-60
AuAu 200 GeV
top 5
STAR Preliminary
dAu
Aoqi Feng, Parallel Talk, 5th February
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Path Length Effects
STAR Preliminary
v2 sys. error
v2RP
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.
v24
AuAu 200 GeV 3lt pTtrig lt 4 GeV/c 1.0 lt pTasso lt
1.5 GeV/c
Away-side features reveal path length effects
Aoqi Feng, Parallel Talk, 5th February
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Eloss probability distribution ?-hadron
correlation

• Provides constraints on Eloss
• probability distributions
• Possibly gives full accounting
• of jet energy loss

T. Renk PRC 74 (2006) 034906
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Results on Medium Response
Parton Eloss
Reappearance of di-jets
Medium 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)
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Conical Emission
Experimental evidence of Conical emission
3 ltpT-trig lt 4 GeV/c 1 lt pT-assoc lt 2 GeV/c

• Two component approach
• Correlated to trigger (jets..)
• Uncorrelated to trigger
• (except via anisotropic flow)
• Bkg normalization 3-particle ZYAM

See also Jason Ulery - Plenary Talk on 8th
February,
Gang Wang (Parallel Talk on 8th Feb
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Mach Cone or Cerenkov Gluons
Cone angle (radians)
STAR Preliminary
pT (GeV/c)

• 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
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Ridge in Heavy Ion Collisions
AuAu
dAu
What does these features reveal about the medium
? Perhaps tells us how the energy lost by partons
are distributed in the medium
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Features of the Ridge (at QM2006)
STAR Preliminary
Yield at large ?? independent on ??
STAR J. Putschke, QM2006
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Different Physics Possibilities
QCD bremsstrahlung radiation boosted by
transverse flow S.A.Voloshin, Phys.Lett.B.
632(2007)490 E.Shuryak, hep-ph0706.3531
In medium radiation and longitudinal flow
push N.Armesto et.al Phys.Rev.Lett. 93(2007)
242301
Broadening of quenched jets in turbulent color
fields A.Majumder et.al Phys. Rev.
Lett.99(2004)042301
Recombination between thermal and shower partons
at intermediate pT R.C. Hwa C.B. Chiu Phys.
Rev. C 72 (2005) 034903
Momentum Kick Model C.Y. Wong hep-ph0712.3282
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

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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 medium
• Ridge 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
Ridge vs. Inclusive
Jet Cone vs. Inclusive
STAR Preliminary
STAR Preliminary
Jet ?/K0s 0.5 lt inclusive Ridge ?/K0s 1
inclusive

• Ratios in cone smaller than inclusive
• Ratios in ridge similar to inclusive

Cristina Suarez - Poster,
Paul Sorenson - Talk 9th Feb, Navneet K. Pruthi -
Poster
Jiaxu Zuo - Poster
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Ridge Di-hadron Correlation w.r.t RP
STAR Preliminary
AuAu 200 GeV
20-60
Observations Ridge decreases with fS. Little
ridge at larger fS. Jet slightly increases with
fS. General agreement with dAu
3lt pTtrig lt 4 GeV/c, pTasso 1.0- 1.5 GeV/c
Interpretation 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
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Ridge 3-particle Correlation
In-medium radiated gluons diffused in??
Jets
In-medium radiated gluons still collimated
Jet fragmentation and diffused gluons
Pawan K. Netrakanti, Plenary Talk, 5th February
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Outlook Di-Jets and Jet Reconstruction
Parton Eloss
Reappearance of di-jets
Medium 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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Di-Jets Triggered Correlations
Observation of di-jets
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Di-Jets Triggered Correlations
No Away-side suppression, No Shape modification,
no ridge
Olga Barannikova, Parallel Talk, 8th February
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Multi-hadron Cluster Triggered Correlations
Motivation Explore jet-biases in di-hadron
correlations Start developing jet reconstruction
Away-side spectrum
0-12 AuAu
Add 12-15 GeV trigger
Multi-hadron trigger
STAR Preliminary
Use cluster energy for trigger - R 0.3 -
pT,seed gt 5 GeV - pT,sec seed gt 3 GeV
Single-hadron and multi-hadron triggers give
similar result Re-confirms single high pT
triggered correlation results probes jet-like
correlations
Brooke Haag - Poster
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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 AuAu collisions compared
• to central CuCu collisions
• CuCu and AuAu zT distributions similar for
  collisions
• with similar Npart - feature not consistent
  with PQM
• calculations
• Path 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

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Summary Medium Response

• Strong jet-medium interaction observed.
• Signals of conical emission observed in central
  AuAu
• 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
• o 3-particle correlations jet
  fragmentation an overall uniform
• excess of associated particles not due to
  correlated emission

STAR Preliminary
Ridge vs. Bulk
STAR Preliminary
Jet Cone vs. Bulk
STAR Preliminary
AuAu
STAR Preliminary
dAu
STAR Preliminary
STAR Preliminary

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Thanks
Thanks to STAR Collaboration
Argonne National Laboratory
Moscow Engineering Physics Institute
Institute of High Energy Physics - Beijing
City College of New York
University of Birmingham
NIKHEF and Utrecht University
Brookhaven National Laboratory
University of California, Berkeley
Ohio State University
Panjab University
University of California - Davis
Pennsylvania State University
University of California - Los Angeles
Institute of High Energy Physics - Protvino
Universidade Estadual de Campinas
Purdue University
Carnegie Mellon University
University of Illinois at Chicago
Pusan National University
University of Rajasthan
Creighton University
Rice University
Nuclear Physics Inst., Academy of Sciences
Instituto de Fisica da Universidade de Sao Paulo
Laboratory of High Energy Physics - Dubna
University of Science and Technology of China
Particle Physics Laboratory - Dubna
Shanghai Institue of Applied Physics
Institute of Physics. Bhubaneswar
SUBATECH
Indian Institute of Technology. Mumbai
Texas AM University
Indiana University Cyclotron Facility
University of Texas - Austin
Institut Pluridisciplinaire Hubert Curien
Tsinghua University
University of Jammu
Valparaiso University
Variable Energy Cyclotron Centre. Kolkata
Kent State University
Wayne State University
University of Kentucky
Institute of Modern Physics, Lanzhou
Warsaw University of Technology
Lawrence Berkeley National Laboratory
University of Washington
Massachusetts Institute of Technology
Institute of Particle Physics
Yale University
Max-Planck-Institut fuer Physics
Michigan State University
University of Zagreb
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Color Factors and q,g Eloss
QCD For SU(3) Nc 3 CA 3 (gluons), CF
4/3 (quarks)



?S 0.119
ALEPH ZPC 76 (1997) 1 OPAL EJPC 20 (2001) 601



SU(3) is the gauge group for QCD
i,j represent fermion field indices and a,b
gauge field indices
An opportunity to relate experimental observable
(of Eloss) to basic ingredient of QCD - Gauge
Group through Color Factors