Search for quarkgluon plasma at RHIC

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Search for quark-gluon plasma at RHIC
Vladislav Pantuev, University at Stony Brook And
in PHENIX collaboration
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• RHIC Relativistic Heavy Ion Collider - is
  addressing 2 fundamental physics questions

how does the nucleon get its spin?
what was the universe 10-6 sec later?
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In the beginning
In 1972 the early universe seemed hopelessly
opaqueconditions of ultrahigh temperaturesproduc
e a theoretically intractable mess. But
asymptotic freedom renders ultrahigh temperatures
friendly Frank Wilczek, Nobel Lecture (RMP 05)
e/T4
Thermal QCD QGP (Lattice)
Before QCD we could not go back further than
200,000 years after the Big Bang. Todaysince
QCD simplifies at high energy, we can extrapolate
to very early times when nucleons meltedto form
a quark-gluon plasma. David Gross, Nobel
Lecture (RMP 05)
Thermal Hadron Gas
Karsch, Redlich, Tawfik, Eur.Phys.J.C29549-556,20
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170 MeV
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Phase Diagram
Transition T 170 MeV e 1.0 GeV/fm3
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RHIC

• Circumference 3.83 km
• Two rings
• Maximum energy (center of mass)
• AuAu up to 200 GeV
• pp up to 500 GeV
• First collisions 2000
• Run 7 about to start

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RHIC after 6 years of running
pp
dAu
AuAu
CuCu
22.4 GeV
62.4 GeV
130 GeV
200 GeV
Reference
sQGP ?
Comp.
Each Run about ½ year, last Run6 was on 12 mln.
donation
p0
h
Current run (?)
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AuAu central collision at vsNN 200 GeV
Side-to-beam view
STAR Experiment at RHIC
Hot Zone
Along-the-beam view
Centrality is determined by Multiplicity Detectors
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JET Tomography
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Nuclear Modification Factor RAA

• Hard processes
• Scale with Ncoll
• reason
• Small cross section
• superposition
• Nuclear Modification-
• Factor RAA

s(AA)/Ncolls(pp)

• In the absence of nuclear effects RAA1 at high
  pT

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RAA Centrality Dependence
p0
AuAu 200 GeV
Run4 Data
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RAA in AuAu at 200 GeV
g
Run4 ?0 Data
p 0
h
Photons are not suppressed p0 and h even at high
pT suppressed Suppression is flat at high pT
!
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RAA Reaction systems

• Geometrical model with corona effect
• More jets from surface
• Correlated with ellipticity

AuAu 30-40 Npart 114
CuCu 0-10 Npart 98.2
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Baryons vs Mesons
Markedly different suppression patterns! below 6
GeV/c. Large change in M/B ratio. Above 5-6 GeV/c
no difference
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Initial state effects? Control measurement in dAu
p0
No strong initial-state effects
!
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Conclusions 1

• Strong jet suppression at high pt
• Factor 5 suppression in most central events, does
  not depend on pt
• Baryons and mesons have different behavior at
  intermediate pt. Baryon excess?
• Direct photons follow N-collision scaling, no
  medium effect
• Initial state effects, like low-x gluon
  saturation, can not explain the observed
  suppression

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Elliptic Flow
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Flow features in experimental observations
Reaction Plane
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Flow unexpected feature of produced medium
Why elliptic flow? - Different pressure gradients
in plane and out of reaction plane.
Sensitive to early evolution

• Mass ordering at low pT
• ideal hydro with early thermalization

Gas of weakly interacting particles can not
produce such flow. Prediction was no/small flow!
P.S. More than 90 of produced particles are at
pt lt 2 GeV/c. The whole bulk of matter flows!
Above pT 2 GeV/c two groups of hadrons ? ?,
K0s, K?, p, ?, ?, ?
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Flow for Light Hadrons
v2 scales with the transverse kinetic energy! As
hydro tells us.
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Flow Light Quarks ? Strange
baryons
mesons
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Flow f meson with mass close to proton mass
mesons vs baryons ? flow scales with nq
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System is in thermal and chemical equilibrium!
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The (s)Quark-Gluon-Plasma ?
Liquid!
Gaseous?
APS The Top Physics Stories for 2005
Free gas of massless quarks and gluons ? No,
strongly coupled!
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The (s)Quark-Gluon-Plasma ?
Liquid!
Gaseous?
APS The Top Physics Stories for 2005
Free gas of massless quarks and gluons ? No,
strongly coupled!
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Conclusions 2

• Strong collective effects in radial and elliptic
  flow
• Constituent quark scaling for v2 suggests
  partonic phase
• V2 is close to ideal hydro limit (low viscosity)
• Wording sQGP strongly interacting Quark-Gluon
  Plasma and even Perfect fluid become popular
• Standard parton energy loss models can not
  explain large v2 at high pt (I did not discuss
  this)

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Jets in Medium
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Di-jets Away-Side Disappearance
STAR PRL 91, 072304 (2003)

• consistent with surface emission
• more intuitive hint for jet suppression, but
  quantitatively much more difficult

hadron --- hadron correlations
Trigger 4-6 GeV/c
Partner 2-PT
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Away-Side Broadening
Decreasing Partner pT
PHENIX PRL 97,052301,2006
STAR Preliminary
hadron --- hadron correlations
Trigger 4-6 GeV/c
Partner 1-2.5 GeV/c
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Pair opening angle
Trigger direction
Cherenkov cone? Unfaivor. Mach cones?
Suggestive of
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Away-Side Emergence
Increasing Partner pT
8 lt pT(trig) lt 15 GeV/c
Fix PT Trig
Raise PT Part
Away side jet remains, but suppressed
Adams et al., STAR nucl-ex/0604018
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Conclusions 3

• Single jet shape does not change
• At pt lt 2.5 GeV/c new collective effect for away
  side jet Mach Cone angular structure
• If both jets are at high pt, there is factor 4-5
  suppression for away side jet

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Heavy Quarks
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PHENIX Non-Photonic Electrons From Charm and
Bottom quarks
Experiment/Theory Ratio 1.72 /-0.02 (stat) /-
0.19 (sys) (0.3 lt pT lt 9.0 GeV/c)
hep-ex/0609010
Theoretical Uncertainty Band
CDF, PRL 91, 241804 (2003)

• hep-ex/0609010 (accepted by Phys. Rev. Lett.)

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Heavy Flavor in AuAu
PHENIX nucl-ex/0611018 (submitted to Phys. Rev.
Lett.)
No suppression at low pT Suppression observed
for pTgt3.0 GeV/c, smaller than for light quarks.
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Heavy Quarks Energy Loss and Flow
nucl-ex/0611018 (submitted to Phys. Rev. Lett.)
Radiative energy loss only fails to reproduce
v2HF. Heavy quark transport model has
reasonable agreement with both RAA and v2HF.
Small relaxation time t or diffusion
coefficient DHQ inferred for charm.
Canonical energy loss models fail to reproduce
data
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AuAu J/?s - Quark Gluon Plasma signature?
Debye screening predicted to destroy J/?s in a
QGP with different states melting at different
temperatures due to different binding energies.
NA50 anomalous suppression
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J/Y Suppression at SPS and RHIC
Suppression patterns are remarkably similar at
SPS and RHIC! Cold matter suppression larger at
SPS, hot matter suppression larger at RHIC,
balance? Recombination cancels additional
suppression at RHIC? How did we get so lucky?
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New Good reference J/Y in pp
Improved Run-5 pp reference data
hep-ex/0611020, PHENIX (submitted to Phys. Rev.
Lett.)
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J/Y RAA in AuAu Collisions
AuAu collisions at 200GeV
Suppression close to light hadrons Less
suppression at central rapidity Suppression is
not solely due to local particle density.
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Rapidity Dependence
Rapidity measured over wide kinematic range for a
variety of centralities and systems.
Significant constraint for recombination
models.
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Momentum spectrum AuAu 200 GeV
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Recent lattice calculations suggest J/? not
screened after all. Suppression only via
feed-down from screened ?C ?, which give 40
of ?
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Regeneration models give enhancement that
compensates for screening?
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Summary J/? Suppression A puzzle of two (or
more) ingredients
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Most recent hits
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STAR coll. - Jet sits on the Ridge?
3ltpt,triggerlt4 GeV pt,assoc.gt2 GeV

• Study near-side yields
• Study away-side correlated yields and shapes
• Components
• near-side jet peak
• near-side ridge
• v2 modulated background

AuAu 0-10 preliminary
3 lt pT(trig) lt 6 GeV2 lt pT(assoc) lt pT(trig)
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Direct g RAA at 200 GeV, Run4
Direct g RAA with measured pp reference data
? p0
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Pion absorption versus angle w.r.t. reaction
plane other way to control thickness of the
medium
Centrality 40-50

• At fixed centrality change parton path length by
  varying f and keeping the same
• Initial conditions
• Longitudinal and transverse expansion

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The results
PHENIX Run2, nucl-ex/0611007, submitted PRC
5 lt pT lt 8 GeV/c
3 lt pT lt 5 GeV/c

• RAA in plane and out of plane changes by factor
  2
• - For peripheral bins no suppression in plane,
  while a factor 2 out of plane

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We vary path length by centrality and angle f,
both results should agree
Variable Le, distance from the center of
interaction region to the edge
60-70

• RAA is universal function of L, not rL
• RAA1 and no energy loss for Le lt 2 fm

10-20
All models are in big trouble! Flow contribution
up to 8 GeV/c? Cronin effect? Something else?
Colors represent different centralities
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Why no absorption? Alternative explanation
Time matters!
see V.P. hep-ph/0506095
Let jets fly in ANY direction
Ncoll distribution in transverse plane, Glauber
Woods-Saxon
Stop jet after some time T. T 2.3 fm/c to
fit peripheral data
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The result
From V.P. hep-ph/0506095
Results of calculation
Describes inclusive RAA and f dependence Describes
v2 at high pT, Simple explanation of lack of
absorption in a layer lt 2 fm, Some other
features
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Final conclusions

• New form of matter is produced at RHIC, sQGP
• Its properties are different from naïve
  expectations of weakly interacting partons
• Medium is more close to liquid in its properties
• There are many parton energy loss models, but no
  good theory
• Big hopes on new approach AdS/CFT correspondence
  and new methods to calculate strongly interacting
  matter
• New impact from conventional plasma theory,
  from dusty plasmas

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Hot questions that RHIC will answer (soon)

• fast thermalization mechanism?
• how low is the viscosity of the liquid?
• response of plasma to deposited energy?
• what is the color screening length?
• nature of phase transition? critical point?
• equation of state of hot QCD matter?

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Russian participation at PHENIX

• IHEP, Protvino
• JINR, Dubna
• Kurchatov Institute, Moscow
• PNPI, Gatchina
• Polytechnic University, St. Petersburg

Around 50 participants (from 400 at PHENIX total)
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Backup
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Calculate elipticity parameter at high pt v2 as
jet surviving probability in and out of plane
Data are for high pt pi0s, PHENIX, blue cicles
4.59 GeV/c, green squares 5-7 GeV/c,
preliminary hep-ph/0506095.No hydro/collective
flow!
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J/Y ltpT2gt
PHENIX ee-
Evaluated for pTlt5 GeV/c where all systems have
data.
New pp reference (ylt0.35)
PHENIX mm-
New pp reference (y in 1.2,2.2)