Experimental study of dense matter at RHIC

1
Experimental study of dense matter at RHIC

• Y. Akiba (RIKEN Nishina Center)
• YITP Symposium
• 2008.03.04

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Outline

• Introduction
• Freezeout/final state
• Hadronization
• Scaling of v2/v4
• Jet quenching at high pT
• Constraining model parameter from RAA
• Modification of jet-correlation shapes
• Ridge?
• J/y suppression
• Heavy quark suppression and flow
• di-leptons
• Thermal(?) photons

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Relativistic Heavy Ion Collider

• Located at BNL
• The first collider of heavy ion
• Top Energy
• sNN1/2 200 GeV for Au-Au
• total s1/2 40 TeV for AuAu
• RHIC Operations
• RUN1(2000) AuAu at 130GeV
• RUN2(2001-2) AuAu/pp at 200GeV
• RUN3(2003) dAu/pp at 200GeV
• RUN4(2004) AuAu/pp at 200 GeV
• AuAu at 62 GeV
• RUN5(2005) CuCu/pp at 200 GeV
• CuCu at 62 and 22 GeV
• RUN6(2006) pp at 200 GeV, 62 GeV
• RUN7(2007) AuAu at 200 GeV
• RUN8(2008) dAu at 200 GeV

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The RHIC Experiments
RHIC
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Formation of dense partonic matter at RHIC

• In 2005, four RHIC experiments published white
  papers that summarized the experimental results
  of the first three years of RHIC operation
• In the white papers, RHIC experiments concluded
  that state of dense partonic matter is formed in
  AA collisions at RHIC
• The conclusion is primarily based on the
  following three pieces of evidence
• Strong suppression of high pT hadrons in AuAu
  (jet quenching)
• Absence of suppression in dAu
• Strong elliptic flow in AuAu
• The next step is to investigate the property of
  the dense matter
• In the following I review the experimental data
  from RHIC.
• Due to my background, most of the data is taken
  from PHENIX

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Hadronic phase/Freeze out
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Hadron spectra thermal freeze-out and radial
flow
PRL72,014903 (PHENIX)

• Hadron spectra are well reproduced by thermal
  distribution with radial expansion (blast wave
  model)
• p/K/p spectra can be simultaneously fit with two
  parameters
• Tfo freezeout temp.
• bT expansion velocity
• Fit results
• Tfo 110 MeV
• bT 0.8 (ltbTgt 0.6)

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Particle ratios Chemical equillibrium
NPA757,184 (PHENIX White Paper)

• Thermal model reproduces hadron ratios.
• Tch 160 MeV, mB 30 MeV
• Evidence for Chemical equillibrium

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3D source imaging
arXiv0712.4372
reverse engineer the correlation function by an
input source function. The analysis suggests that
there is a long tail of the source
distribution Solutoin of the long-standing HBD
puzzle?
3D source imaging reconstructs source parameters
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Hadronization
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Scaling of v2 of hadrons
PRL98_162301

• More data on v2(pT) of hadrons are accumulated
• When v2/nq vs KET/nq (KETtransverse kinetic
  enery), all data points are on a universal curve,
  suggesting that v2 developed in partonic stage

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More on the scaling of v2 phi flow
PRL99_052301
Phi meson (small interaction cross section) also
follows the number of quark (nq) scaling.
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v4 - scales with v2
V4
V4/(nq)2
V4
pT (GeV/c)
KET /nq (GeV/c2)
KET (GeV/c2)
v2 scales with nq, v4 with nq2 partonic
degree of freedom
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High pT hadrons --- energy loss in QGP
High pT hadron Jet modificaiton J/psi Heavy
quarks Dileptons Thermal photon
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p0 pT spectra at vsNN 200 GeV
RAA measurements now extends to 20 GeV/c
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RAA of hadrons and direct photon (AuAu 200GeV)

• Same suppression pattern for p0 and h
  Consistent with parton energy loss and
  fragmentation in the vacuum
• RAA for fs larger than ?0 RAA for 2 lt pT lt 5
  GeV/c. Why?
• Ncoll scaling for direct g (except for highest pT
  point? Isospin effect?)

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Quantitative analysis (model dependent)
arXiv0801.1665
Quantitative comparison with PQM model
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Quantitative analysis (more)
Comparison with GRV model dNg/dy1400
arXiv0801.1665
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RAA beam energy dependence (CuCu)
?? CuCu 22,62,200 GeV (Run 5)
arXiv0801.4555
g

• Model calculations indicate quenching expected at
  ?sNN 22 GeV, but Cronin effect dominates
• Species dependence to probe space/time of
  suppression

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High pT hadrons --- energy loss in QGP
High pT hadron Jet modificaiton J/psi Heavy
quarks Dileptons Thermal photon
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Jet correlation
Recoil particles to central arm
PRD74,072002
pp collisions at 200 GeV
High pT trigger p0 to central arm EMCAL
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Modification of jet correlation

• This is another surprise two particle of two
  high pT track (jet correlation) is modified in
  central AuAu collisions.
• Many theory attempts to explain this effect, but
  no consensus reached yet.

AuAu
PRL97,052301 (2006)
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More detailed study of jet correlation
PRL98_232302
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h-h correlations - jet functions
unchanged near-side peak in the final jet
functions when moving away from Reaction plane,
indication for away side modification.
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The Ridge?
Ridge
Jet
STAR QM2006
Bulk Medium
In QM2006, STAR shows that there is
Ridge, Enhancement in small Df and large Dh of
leading particle This is the latest surprise in
jet correlation in AuAu This becomes a hot topic
in QM2008
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Is there Ridge? Apparently

• In QM2008, both PHENIX and PHOBOS shows that they
  also see Ridge
• However, I myself is still skeptical about it.
• The cause can be different from medium response.
• It is difficult to imagine that information can
  propagate for a wide rapidity gap.
• Speculation is it residual of v2 due to
  non-linear interaction between jets and v2?

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J/psi --- probe of deconfinement(?)
High pT hadron Jet modificaiton J/psi Heavy
quarks Dileptons Thermal photon
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J/y suppression

• A quark gluon plasma has been predicted to
  suppress J/? production
• Interesting suppression patterns have been
  observed at lower energies at the CERN SPS (NA50,
  NA60)
• Rapidity and transverse momentum provide
  additional model constraints

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J/y in pp
PRL98_232002

• Order of magnitude higher statistics than the
  previous measurement by PHENIX
• Pt and rapidity distribution are determined
• Baseline for J/y suppression in AA

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J/y suppression in AuAu
PRL98_172301

• High statistics measurement of J/y in AuAu in
  wide rapidity range
• Mid-rapidty J/y ? ee
• Forward rapidty J/y?mm
• Strong suppression of J/y is observed
• Consistent with the prediction that J/ys are
  destroyed in de-confined matter
• Surprisingly, the suppression is stronger at
  forward rapidity than in mid-rapidity
• J/y formation by recombination of charm pairs in
  deconfined matter?

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RAuAu (run 4) RAuAu (run 7)
NEW

• Forward rapidity only (for now)
• More bins at higher centrality
• Confirm the trend
• RAA(y1.7) lt RAA(y0)

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J/? dAu Cold Nuclear Matter
PRC77_024912 (just publised)
J/? RdAu 200 GeV

• Increased Run 5 pp statistics (x10 Run 3) as
  baseline
• Improved consistent pp and dAu analysis
• Improved alignment, resolution, yield
  extraction,
• Cancellation of systematic errors in RdAu
• Result CNM Shadowing(EKS) ?Breakup 2.8
  mb
• Consistent within errors with previous results
• and with ?Breakup4.2/-0.5mb (SPS result)

1.7 -1.4
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J/? AuAu CNM Effects
J/? RAuAu 200 GeV (Run4)
PRC77_024912
1.2 lt y lt 2.2

• Large errors still (need Run 8 dAu, Run 7 AuAu)
• Comparison suggests more forward suppression
  beyond CNM than at mid-rapidity
• BUT models shown dont describe RdAu impact
  parameter dependence

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J/? RAA CuCu and AuAu
J/? RAA 200 GeV

• Approx 2x more J/? in CuCu sample than AuAu
  sample
• More precise Npartlt100 info
• Curves show RAA prediction from ad hoc CNM fit to
  RdAu separately at y0 and y gt 1.2
• CNM from RdAu fit describes suppression for Npart
  lt 100.

arXiv0801.0220

• RdAu constraints are not sufficient to say if
  suppression beyond cold nuclear matter is
  stronger at forward rapidity

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RHIC run 8 dAu 30 x run 3 !

• Lets wait for this run analysis before to say
  more about cold matter (and derive decent
  survival probabilities)

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Heavy quarks
High pT hadron Jet modificaiton J/psi Heavy
quarks Dileptons Thermal photon
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Open Charm via Semi-Leptonic Decays
Due to its heavy mass, charm can only be produced
in early stage of collision. It can be used as
probe of hot dense matter. Open charm can be
measured through single leptons
e
p0
D0
For example
K
m-
nm
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Heavy flavor production in pp
Phys. Rev. Lett 97,252002 (2006)

• Single electrons from heavy flavor (charm/bottom)
  decay are measured and compared with pQCD theory
• The new data extends the pT reach to 9 GeV/c
• FONLL pQCD calculation agree with the data

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Heavy Flavor in AuAu
PRL98_172301
No suppression at low pT Suppression observed
for pTgt3.0 GeV/c, smaller than for light quarks.
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Comparison with models RAA v2
PRL98_172301

• Two models describes strong
• suppression and large v2
• Rapp and Van Hee
• Moore and Teaney
• From model comparison,
• viscosity to entropy ratio h/s
• can be estimated
• DHQ 2pT 4 - 6
• DHQ 6 x h/(ep) 6 x h/Ts
• ? h/s (4/3 2)/4p
• The estimate of h/s is close
• to the conjectured bound
• 1/4p from AdS/CFT

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Bottom Measurement
pp 200 GeV Charm and bottom extracted via e-h
mass analysis

• Charm and bottom spectra both ?x? above FONLL
  calculations
• But ratio is in good agreement with FONLL

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Is bottom also suppressed? Does it flow?

• pp data indicates that a large contribution of b
  for pTgt2 GeV/c
• The suppression in high pT is strong and new v2
  data suggest significant flow of HF electron in
  high pT
• Is bottom also suppressed?
• Does bottom also flows?

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Low mass dileptons
High pT hadron Jet modificaiton J/psi Heavy
quarks Dileptons Thermal photon
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Measured pp Mee compared to Cocktail

• Cocktail filtered in PHENIX acceptance
• Charm, Bottom, DY contributions from PYTHIA
• Excellent agreement!

arXiv0802.0050
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Heavy Quarks in pp from ee-
After subtraction of Cocktail -
Fit to acharm bbottom (with PYTHIA shape)

• Good agreement with single e results
• Also new analyses via e-h coincidences, single
  muons, and direct charm measurement

arXiv0802.0050
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total cross section of charm and bottom
vs dependence of cross section with NLO
pQCD agrees with data
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AuAu Mee compared to Cocktail

• Data and Cocktail absolutely normalized
• Cocktail normalized to AuAu measurements
• Except ccbar
• Low mass excess
• 150 lt Mee lt 750 MeV
• X 3.40.2(stat.) 1.3(syst.)0.7(model)

arXiv0706.3034
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PT Dependence of AuAu Mee

• Low Mass excess is a low pT enhancement
• Huge excess at lowest pT
• Late Phase info

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Thermal photons --- probe of initial T
High pT hadron Jet modificaiton J/psi Heavy
quarks Dileptons Thermal photon
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Thermal Photons from the hot matter
If the dense matter formed at RHIC Thermailzed,
it should emit thermal radiation. This is
black body radition from the hot matter and the
direct evidence of thermalization in early
stage The temperature of the matter can directly
measured from the spectrum of thermal
photon. Measurement is difficut since the
expected signal is only 1/10 of photons from
hadron decays
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Enhancement of almost real photon

• QM2005
• Results from AuAu
• QM2008
• long awaited result from pp
• important confirmation of method
• pp
• Agreement of pp data and hadronic decay cocktail
  
• Small excess in pp at large mee and high pT
• AuAu
• data agree for mee lt50MeV
• Clear enhancement visible above for all pT

PHENIX Preliminary
1 lt pT lt 2 GeV 2 lt pT lt 3 GeV 3 lt pT lt 4 GeV 4 lt
pT lt 5 GeV
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Direct ? Yield from ?

• Virtual ??with pT gtgt mee should be produced
  directly with a rate and mass distrib. that
  follows a Dalitz form fdir with MHad-gtoo
• Extract Direct ? excess as fraction r of fdir
  needed to describe low mass excess
• That direct ? fraction of inclusive ? (mostly
  ???and ?) should be the same as the real ?
  fraction of inclusive ?? (mostly ???and ?)

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Fraction of direct photons

• Fraction of direct photons
• Compared to direct photons from pQCD
• pp
• Consistent with NLO pQCD
• favors small µ
• AuAu
• Clear excess above pQCD

pp
AuAu (MB)
µ 0.5pT µ 1.0pT µ 2.0pT
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Direct ? via ? for pp, AuAu

• New pp result with ? method agrees with NLO
  pQCD predictions, and with statistical method at
  high pT
• Confirmation of the method
• For AuAu (QM05 result) there is a significant
  low pT excess above pp expectations
• If the direct photon in the AuAu is thermal
  origin, the initial temperature of the matter can
  be determined

arXiv0801.xxxx
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Summary
Towards an unified description of the entire time
evolution