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![Page 1: Search for quark-gluon plasma at RHIC Vladislav Pantuev, University at Stony Brook And in PHENIX collaboration.](https://reader035.fdocuments.in/reader035/viewer/2022062305/5697bf7a1a28abf838c831a1/html5/thumbnails/1.jpg)
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
what was the universe 10-6 sec later?
how does the
nucleon get its spin?
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Karsch, Redlich, Tawfik, Eur.Phys.J.C29:549-556,2003
In the beginning…
Thermal QCD ”QGP” (Lattice)
/T4
“In 1972 the early universe seemed hopelessly opaque…conditions of ultrahigh temperatures…produce a theoretically intractable mess. But asymptotic freedom renders ultrahigh temperatures friendly…” Frank Wilczek, Nobel Lecture (RMP 05)
“Before [QCD] we could not go back further than 200,000 years after the Big Bang. Today…since QCD simplifies at high energy, we can extrapolate to very early times when nucleons melted…to form a quark-gluon plasma.” David Gross, Nobel Lecture (RMP 05)
170 MeV
Th
erm
al
Ha
dro
n G
as
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Phase Diagram
Measurement of transverse energy: Initial energy density significantly above Trans
Transition: T ~ 170 MeV
~ 1.0 GeV/fm3
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RHIC • Circumference: 3.83
km• Two rings• Maximum energy
(center of mass)
– Au+Au: up to 200 GeV– p+p: up to 500 GeV
• First collisions 2000• Run 7 about to start
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p+p d+Au Au+Au Cu+Cu
200 GeV
130 GeV
62.4 GeV
22.4 GeV
Reference sQGP ? Comp.
RHIC after 6 years of running
0 Current run (?)Each Run about ½ year, last Run6 was on $12 mln. donation
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Side-to-beam view
Along-the-beam view
Hot Zone
Au+Au central collision at √sNN = 200 GeV
STAR Experiment at RHIC
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
evt 2AB AB T
AB 2AB pp T
1 N d N /dydpR
T d /dydp
• In the absence of nuclear effects: RAA=1 at high pT
no effect
= (A+A)/[Ncoll*(p+p)]
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RAA : Centrality Dependence
Run4 Data
Au+Au 200 GeV
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Run4 0 Data
RAA in AuAu at 200 GeV
Photons are not suppressed
and even at high pT suppressedSuppression is flat at high pT
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RAA – Reaction systems
• Geometrical model with “corona” effect
– More jets from surface – Correlated with ellipticity
Au+Au30-40%
Npart
= 114
Cu+Cu0-10%
Npart
= 98.2
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Baryons vs
MesonsMarkedly 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 d+Au
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:
xz
y
1
2
3
3
cos212
1
nn
TT
nvdydpp
Nd
pd
NdE
Reaction Plane
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Why elliptic flow? - Different pressure gradients in plane and out of reaction plane. Sensitive to early evolution
Flow – unexpected feature of produced medium
PRC (72), 014904 (2005) Mass ordering at low pT:ideal hydro with early thermalization
Above pT ~2 GeV/c two groups of hadrons:
, K0s, K,
p, Λ, ,
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 < 2 GeV/c. The whole bulk of matter flows!
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Flow for Light Hadrons
TT KEp
v2 scales with thetransverse kineticenergy! As hydro tells us.
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Flow: Light Quarks → Strange
baryonsbaryons
mesonsmesons
Quark content determines v2
Simplistic hadronization model :v2q = v2h(pT/n)/n
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mesons vs baryons flow scales with nq
Flow: meson with mass close to proton mass
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System is in thermal and chemical equilibrium!
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The (s)Quark-Gluon-Plasma ?
APS: The Top Physics Stories for 2005
Free gas of massless quarks and gluons ?No, strongly coupled!
Liquid!
Gaseous?
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The (s)Quark-Gluon-Plasma ?
APS: The Top Physics Stories for 2005
Free gas of massless quarks and gluons ?No, strongly coupled!
Liquid!
Gaseous?
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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
• 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
STAR PRL 91, 072304 (2003)
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PHENIX PRL 97,052301,2006
STAR Preliminary
Away-Side BroadeningDecreasing Partner pT
hadron --- hadron correlations
Trigger: 4-6 GeV/c
Partner: 1-2.5 GeV/c
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h± --- h±
C: VariousT: 2.5 - 4
P: 1 - 2.5
Trigger direction
Pair opening angle
Suggestive of…Cherenkov cone? Unfaivor. Mach cones?
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Away-Side Emergence
8 < pT(trig) < 15 GeV/c
Adams et al., STAR nucl-ex/0604018
Increasing Partner pT
Fix PT Trig
Raise PT
Part
Away side jet remains, but suppressed
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Conclusions 3
• Single jet shape does not change
• At pt < 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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~factor 2
D0
PHENIX Non-Photonic Electrons –
From Charm and Bottom quarks
Experiment/Theory Ratio: 1.72 +/-0.02 (stat) +/- 0.19 (sys)(0.3 < pT < 9.0 GeV/c)
hep-ex/0609010
hep-ex/0609010 (accepted by Phys. Rev. Lett.)
CD
F,
PR
L 91
, 24
1804
(2
003)
Theoretical Uncertainty Band
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Heavy Flavor in Au+Au
No suppression at low pT
Suppression observed for pT>3.0 GeV/c, smaller than for light quarks.
PHENIX nucl-ex/0611018(submitted to Phys. Rev. Lett.)
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Heavy Quarks Energy Loss and Flow
Radiative energy loss only fails to reproduce v2
HF.
Heavy quark transport model has reasonable agreement with both RAA and v2
HF.
Small relaxation time or diffusion coefficient DHQ
inferred for charm.
nucl-ex/0611018(submitted to Phys. Rev. Lett.)
“Canonical” energy loss models fail to reproduce data
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Debye screening predicted to destroy J/ψ’s in a QGP with different states “melting” at different temperatures due to different binding energies.
AuAu J/ψ’s - Quark Gluon Plasma signature?
Color Screening
cc
NA50 anomalous suppression
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J/ 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”?
NA50 at SPS (0<y<1)PHENIX at RHIC (|y|<0.35) eePHENIX at RHIC (1.2<|y|<2.2)
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New: Good reference: J/ in p+pImproved Run-5 pp reference data
hep-ex/0611020, PHENIX(submitted to Phys. Rev. Lett.)
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J/ RAA in Au+Au Collisions
Suppression close to light hadrons
Less suppression at central rapidity
Suppression is not solely due to local particle density.
Au+Au collisions at 200GeV
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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 Au+Au 200 GeV
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Recent lattice calculations suggest J/ψ not screened after all.Suppression only via feed-down from screened C & ’, which give ~40% of
Quarkonium dissociation temperatures – Digal, Karsch, Satz
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Regeneration models give enhancement that compensates for screening?
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Summary – J/ SuppressionA puzzle of two (or more) ingredients
0 mb
3 mb
Low x2 ~ 0.003(shadowing region)
CNM needs better data constraint
Experimental homework
nucl-ex/0611020
Regeneration compensates for strong destruction?
Theoretical homework
0 = 1 fm/cused here
SPS overall syst (guess) ~17%
PHENIX overall syst ~12% & ~7%
difficult to compare RHIC to SPS suppression – but may be similar
Sequential screening and forward-y gluon saturation?
nucl-ex/0611020
Forward/mid rapidity suppression ratio saturates @~0.6
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Most recent hits
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Study near-side yields
Study away-side correlated yields and shapes
Components near-side jet peak
near-side ridge
v2 modulated background
STAR coll. - Jet sits on the Ridge?
3<pt,trigger<4 GeV
pt,assoc.>2 GeVAu+Au 0-10%
preliminary
d+Au, 40-100% Au+Au, 0-5%
3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)
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Direct RAA at 200 GeV, Run4
Direct RAA with measured
p+p reference data
η π0
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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 and keeping the same :
•Initial conditions
• Longitudinal and transverse expansion
12
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The results:
3 < pT < 5 GeV/c 5 < pT < 8 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
PHENIX Run2, nucl-ex/0611007, submitted PRC
13
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We vary path length by centrality and angle , both results should agree
Colors represent different centralities
RAA is universal function of Lnot L
RAA~1 and no energy loss for L < 2 fm
Variable L, distance from the
center of interaction region to the edge
60-70%
10-20%
All models are in big trouble!
Flow contribution up to 8 GeV/c?
Cronin effect?
Something else?
14
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Why no absorption? Alternative explanation: Time matters!
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
see V.P. hep-ph/0506095
16
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The result:
Results of calculation
Describes inclusive RAA and dependence
Describes v2 at high
pT,
Simple explanation of lack of absorption in a layer < 2 fm,
Some other features
17
From V.P. hep-ph/0506095
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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/ <pT2>
New p+p reference (|y|in [1.2,2.2]):
Evaluated for pT<5 GeV/c where all systems have data.
New p+p reference (|y|<0.35):
222 /cGeV 14.006.037.3 Tp
222 /cGeV 15.018.007.4 Tp
PHENIX e+e-
PHENIX +-