Azimuthal Anisotropy and the QGP

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Azimuthal Anisotropy and the QGP

• Yasuo MIAKE, Univ. of Tsukuba

1. Why I Iike azimuthal anisotropy
2. Tsukuba strategy for RHIC-PHENIX
3. What is found at RHIC

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Reasons why I love azimuthal anisotropy

• Info. on mean free path ? vs. R
• Anisotropy of the coordinate space converted to
  that of the momentum space.
• Clear origin of the signal !
• Geometry is clear
• From eccentricity to v2
• Centrailty dependence gives good tests
• Sensitivity to the early stage of collisions !

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Sensitivity to the early stage
RQMD
Kolb et.al., PRC62(2000)054909
Time

• Anisotropy in coordinate space disappears quickly
• Ratio of eccentricity after a time delay
• Disappears quickly
• ? v2 senses early stage of collision

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Key1 reliable R.P. determination

• Wide rapidity gap from central detector
• Free from other source of corr such as HBT,
  decays, jets auto-corr.
• Corr. between SMD(spect) and BBC(part) also
  confirmed
• ?R.P. determination from whole event wide

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Key2 PID with TOF Aerogel

• High resolution TOF and low index of 1.01 Aerogel
  Cherenkov
• Both Tsukuba contribution

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What we expected before RHIC

• There is a tendency of saturation!?
• Hadron cascade predicts a few .

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Surprise !

• Early compilation

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Large azimuthal anisotropy
PHOBOS nucl-ex/0406021

• Larger in higher energies.
• Increase with pt and saturate

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Failure of hadronic scenarios
M. Bleicher, H. Stocker Phys. Lett. B526 (2003)
309

• Hadronic scenario underestimates v2 at RHIC.
• v2 1 - 2
• System thermalized early with the mechanism other
  than hadronic rescatterings.

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v2 vs. Eccentricity
Phenix PRL 89(2002)212301

• At low pt region, the ratio stays constant
• Eccentricity scaling observed in comparison of
  AuAu, CuCu
• ?Scaling with eccentricity shows v2 builds up at
  early stage

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v2 with particle identification
PHENIX P.R.L. 91, 182301 (2003)

• Low pt region
• v2(?) gt v2(K) gt v2(p)
• Mass Ordering
• Good agreement with hydrodynamics
• Very early thermalization (0.6 fm/c) high
  energy density (20 GeV/fm3) required !
• ?More from Hiranos talk
• Perfect fluid (low viscous)
• What brings the system thermalization in such a
  short time!
• ?Partonic degree of freedom
• Deviations at high pt region (gt 1.5 GeV/c)
• v2(?,K) lt v2(p)
• Meson vs Baryon?
• Other mechanism?

PHENIX Preliminary Masui_at_QM05
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Mass Ordering in single spectra
PHENIX, PRC69,034909(2004)
AuAu at 200 GeV/n
Collective Flow

• Exponential in mt for low pt region
• Known from AGS SPS era
• Mass ordering of slope parameters
• Proof of hydrodynamical collective flow

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Other surprise baryon dominance

• We had many reasons to consider gt 2GeV/c is the
  jet region.
• In peripheral, p/? ratio similar to those in
  ee/pp suggesting fragmentaton process.
• Fragmentation process should show np lt n? as seen
  in ee/pp.
• In central AuAu, p/? ratio increases with
  centrality, suggesting other mechanism.

Phenix P.R.L. 91(2003)172301
? High resolution Time-of flight detector
? Quark Recombination Model (Quark Coalescence
Model)
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Quark recombination model (RECO)

• Quarks, anti-quarks combine to form mesons and
  baryons from universal quark distribution, w(pt).

Characteristic scaling features expected. ?Quark
number scaling
Because of the steep distr. of w(pt), RECO wins
at high pt even w. small Cx.
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Proton dominance by RECO

• Recombination model explains the proton dominance.

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V2 from RECO

• Characteristic scaling behavior

Azimutal distr. of meson (2q)
Azimuthal distr. of baryon (3q)
Azimuthal distr of quark w
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Quark number scaling observed!

• Quark number scaling clearly observed in v2.
• Distinct difference between Baryon Meson also
  seen in RCP, yield ratio of central and
  peripheral coll.

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Mass ordering of quarks?
WWND 2006, M. Issah
KET mT m
Kinetic energy of constituent quarks

• Accidental OR ordering in mass of quarks?
• Existence of hypersurface where QGP converted to
  hadrons?

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Study of electron for charm

• Origins of electrons
• photonic
• Dalitz decays of ?????????
• Photon conversions
• non-photonic
• Semi-leptonic decays of heavy flavored mesons
• ?Electron yields are consistent with those
  photonic charm decays.

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Charm v2 from electrons
S.Esumi S. Sakai_at_SQM2006

• Measure v2 of inclusive electrons
• Evaluate contribution of photonic electron
• Cocktail Method
• Converter Method
• Then, subtract !

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Charm seems to flow!
S.Esumi S. Sakai_at_SQM2006

• Data seem to favor the flow of the charm.
• If so, thermalized flowing charm supports
  quark-coalescence formation of QGP.

V.Greco, C.M.Ko, R.Rapp,PLB595(2004)202.
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Study of direct photon
PHENIX, PRL 96,032302(2006)

• Pi-zero results consistent with other mesons
• No significant diff. btwn inclusive v2 and
  expected photon v2 from hadronic decay (pion,
  eta, etc)
• Direct photons are from compton-like prompt
  process?

R direct photon excess ratio
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Summary of my talk

• v2 is fun!
• Establishment of R.P. is great !
• v2 is even useful !
• Sensitive to the early stage of collisions
• Thermalization as early as 0.6 fm/c
• Large azimuthal anisotropy cannot be generated
  with hadronic process.
• Support the quark recombination model
• Collectivity at parton level
• Phenomenological, but universal quark
  distribution function!
• ?statistical description of quarks ?QGP
• Much fun to come
• Charm photon !

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