Direct photons for the UHKM package

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Direct photons for the UHKM package

• Sergey Kiselev, ITEP, Moscow
• Direct photon news
• new experimental techniques
• new physical processes
• new data
• Photons for the UHKM package
• decay ?
• prompt ?
• thermal ?
• hard-thermal ?
• Conclusions

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New experimental techniques

• Last years large progress in experimental
  techniques to extract direct photons
• Direct photons have been revealed by methods
• Subtraction, WA98/2000, PHENIX/2005
• Momentum correlation, WA98/2004
• Internal conversion, PHENIX/2005, QM05
• External conversion, PHENIX/2006, QM06
• Tagging, PHENIX/2006, QM06

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New physical processes
Photons in AA
Direct Photons
Decay Photons
jet-g-conv.
hard
thermal
hardthermal
Preequilibriumphotons ???
QGP
Hadron gas
direct
fragmentation
Medium inducedg bremsstr.
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New physical processes - RHIC
PR C69 014903 (2004) S.Turbide et al.
2006 hep-ph/0609301
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New data RAA
Nucl-ex/0701040

• RAA seems to be below unity at very high-pT (pT gt
  14 GeV/c)
• None of the theoretical calculations reproduces
  RAA in the full pT range

First data using pp data as reference!
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New data v2
Within statistical and systematic errors v2 is
consistent with zero. v20 or cancellation of
different contributions?
S.Turbide, C.Gale, R.J.Fries, PRL 96 032303 (2006)
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UHKM package

• Universal Hydro Kinetic Model (UHKM)
  (http//uhkm.jinr.ru). Now includes
• FASTMC FAST Monte-Carlo hadron freeze-out
  generator. Particles are generated on the
  chemical or thermal freeze-out hyper-surface
  represented by a parameterization or a numerical
  solution of relativistic hydrodynamics.
• UKM Universal Kinetic Model. Treats further
  evolution (scattering and decays) solving
  relativistic Boltzmann equations numerically.
• SPHES Smoothed Particle Hydrodynamics
  Equations Solver. Solves (13D) relativistic
  perfect hydrodynamics equations at given initial
  condition and equation of state and provides
  hadron freeze-out hyper-surface.

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photons for UHKM

• decay photons trivial (p0, ?, decays)
• prompt photons (high pT)
• pp data fit
• AB binary scaling
• thermal photons (low pT)
• thermal rates from QGP/HadronGas have to be
  convoluted over the space-time history of the AB
  reaction given by hydrodynamics
• hard-thermal (intermediate pT)
• ? Should think how jet-? conversion,
  jet-bremsstrahlung could be implemented in UHKM.
  L.Malinina plans to implement jets. May be, in
  parallel, one can think on direct photon source.

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Prompt photons data fit
A Compilation of Data, J. Phys. G, 23 (1997)
A1 Data fit D.Srivastava, Eur.Phys.J, C22 (2001)
129
pp
AB Ed3N/d3p(b)Ed3spp /d3p AB TAB
(b)Ed3spp/d3p Ncoll(b)/sppin
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Prompt photons RHIC pp data
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Thermal photons

• Thermal rates from QGP
• Perturbative QCD, the lowest order in ?s
• qq ? g? qg ? q?
• dN/d4xd3p ? ??s ln(0.23E/?sT) exp(-E/T) T2/E,
  ZP C53, 433
• bremsstrahlung
• dN/d4xd3p ? ??s exp(-E/T) T2/E, PL B510, 98
• Thermal rates from HG
• effective theory for hadron interactions
• p? ? p? pp ? ?? ? ? p?
• dN/d4xd3p ? T2.15 exp(-E/T) / exp((1.35
  ET)0.77), PL B510, 98
• The thermal rates can be convoluted over the
  space-time history of the AB reaction given by
  SPHES

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Conclusions

• Progress in the direct photon sector as in
  experimental methods and theory
• One can implement photons in the UHKM package
• - decay photons
• - prompt photons
• - thermal photons
• Should think on the hard-thermal source of photons

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Back up
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There are theoretical predictions with a sizable
azimuthal parameter v2
Thermal photons are produced throughout the
expansion history and reflect quark anisotropy
Jets lose more energy where the medium is thicker
- more jet-photon conversions (v2lt0), photons
from fragmentation of quenched jets (v2gt0)
S.Turbide, C.Gale, R.J.Fries, PRL 96 032303 (2006)
R. Chatterjee et al., PRL 96, 202302 (2006)
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How does PHENIX measure direct photons and v2?

• Measure inclusive photon yield, Ninc
• Measure hadron contribution components p0 and h
• By Monte Carlo calculate p0 and h decay
  background in inclusive sample, Nbg
• Calculate direct photon excess over hadron
  decays, R
• Measure inclusive and hadron v2 by reaction plane
  method
• Calculate direct photon v2 as

R v2inc v2BG
v2dir
R 1
Use large statistics Run 4 AuAu data set
R N inc / NBG
See also poster 86 by Kentaro Miki
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In pp Hard photonsdirect component
Annihilation
Compton
In AA picture is much more complicated
Photons in AA
Direct Photons
Decay Photons
Preequilibriumphotons
hard
thermal
hardthermal
QGP
Hadron gas
direct
fragmentation
jet-g-conv.
Medium inducedg bremsstr.
V20
V2gt0
V2gt0
V2gt0
V2lt0
V2lt0