28.05.08itep meeting s.kiselev1 fast generators of direct photons sergey kiselev, itep, moscow ...
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28.05.08 ITEP meeting S.Kiselev 1
Fast generators of direct photons
Sergey Kiselev, ITEP, Moscow Introduction
Definitions SPS and RHIC data New processes
Prompt photons Thermal photons in 1+1 hydrodynamics
Hot Hadron Gas (HHG) scenario Qurk Gluon Plasma (QGP) scenario
To do
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Introduction
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Introduction - definitions
Direct photons: not from hadron decays Quark gluon level:
qq gγ, qg qγ, qq(g) qq(g)γ.
Initial hard NN collisions, pQCD prompt γ Thermalised QGP stage thermal γ from QGP.
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Introduction – definitions
Hadron level: meson scatterings: ππ ργ, πρ πγ, πK K* γ, Kρ
Kγ, KK* πγ, πK* Kγ, . . . Thermalised hadron stage thermal γ from HHG
Decay photons: Long lived (c » cAB ~ 50-100 fm)
π0 γγ, γγ, ’ ργ/ωγ/2γ Shot lived (c cAB ~ 50-100 fm)
ω πγ, a1 πγ, Δ Nγ, K* Kγ, γ, ρ ππγ, . . .
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Introduction – SPS data
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Introduction – RHIC data
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Photons in A+A
Direct PhotonsDecay Photons
hard thermal hard+thermal
QGP Hadron gas`direct` fragmentation
Preequilibriumphotons ???
jet--conv.
Medium induced bremsstr.
Introduction - new processes at RHIC
Hard scattered parton interacts with gluon in bulk matter
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Prompt photons: pp data fit + binary scaling
PHENIX hep-ph/0609037
(√s)5 Ed3σ/d3p = F(xT,y) One can use a data tabulation of
the F(xT,y) to generate prompt photons.
A+B:
Ed3N/d3p(b)=
Ed3σpp/d3p AB TAB(b)=
Ed3σpp/d3p Ncoll(b)/σppin
Nuclear effects (Cronin, quenching, …) are not taken into account.
Realization: GePP.C macros for ROOT
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Generator of Prompt Photons (GePP): results
Comparison with RHIC data Prediction for LHC
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Bjorken -(1+1)-HydroDynamics (BHD)
Proper time and rapidity y Phys.Rev.D27(1983)140
There is no dependence onLorenz boost variable y:
Landau hydrodynamical model, viscosity and conductivity are neglected
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Photon spectrum in BHDPhoton spectra follow from convoluting the photon production rates with the space–time evolution of the collision
For a longitudinally expanding cylinder
For proper time and rapidity y`
For an ideal gas
Main parameters: initial 0 , T0 and Tf (at freeze-out)
Connection with the local rest frame
Input function – production rate E dN/d4xd3p (E,T)
Phys.Rep.364(2002)98
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HHG scenario
C.Song, Phys.Rev.C47(1993)2861 an effective chiral Lagrangian with π, ρ and a1 mesons to calculate the processes ππ →ργ , πρ → πγ, and ρ →ππγ .
C.Song and G.Fai, Phys.Rev.C58(1998)1689.
parameterizations for photon rates.
Realization: GeT_HHG.C macros for ROOT
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GeT_HHG: comparison with SPS and RHIC
Choosing T0 and 0 one can fit data in the hadron scenario
comparison with data, Tf = 100 MeV
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GeT_HHG: prediction for LHC
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GeT_HHG: sensitivity to the parameters
sensitivity to T0 sensitivity to Tf
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QGP scenario: QGP and HHG phasesQGP: ideal massless parton gas (µq =0) HHG: ideal massless pion gas
First order phase transition at critical temperature Tc
B bag constant
Nc colorsNf flavors
g number of degrees of freedom
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QGP scenario: mixed phase
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Mixed phase
Main parameters: initial 0 , T0 , Tc and Tf
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Rates from QGP -1st order
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Perturbative thermal QCD applyingHard thermal loop (HTL) resummation
Phys.Lett.B510(2001)98
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Rates from QGP -2nd order
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Thermal photon production in the QGP is a non-perturbative mechanism that can not be accessed in perturbative HTL resummed thermal field theory
2-loop contribution is the same order in αs
One must consider the QGP rates as an educated guess
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To do
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• Write and test the macros GeT_QGP.C• Think on the “hard+thermal” generator