ITEP meeting S.Kiselev1 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

Introduction ITEP meeting S.Kiselev2

ITEP meeting S.Kiselev3 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.

ITEP meeting S.Kiselev4 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  » c  AB ~ fm) π 0  γγ,   γγ,  ’  ργ/ωγ/2γ Shot lived (c   c  AB ~ fm) ω  πγ, a 1  πγ, Δ  Nγ, K *  Kγ,    γ, ρ  ππγ,...

Introduction – SPS data ITEP meeting S.Kiselev5

Introduction – RHIC data ITEP meeting S.Kiselev6

ITEP meeting S.Kiselev7 Photons in A+A Direct PhotonsDecay Photons hardthermalhard+thermal QGPHadron gas`direct`fragmentation Preequilibrium photons ??? jet-  - conv. Medium induced  bremsstr. Introduction - new processes at RHIC Hard scattered parton interacts with gluon in bulk matter

ITEP meeting S.Kiselev8 Prompt photons: pp data fit + binary scaling  PHENIX hep-ph/ (√s) 5 Ed 3 σ/d 3 p = F(x T,y)  One can use a data tabulation of the F(x T,y) to generate prompt photons.  A+B: Ed 3 N/d 3 p(b)= Ed 3 σ pp /d 3 p AB T AB (b)= Ed 3 σ pp /d 3 p N coll (b)/σ pp in  Nuclear effects (Cronin, quenching, …) are not taken into account.  Realization: GePP.C macros for ROOT

ITEP meeting S.Kiselev9 Generator of Prompt Photons (GePP): results Comparison with RHIC data Prediction for LHC

ITEP meeting S.Kiselev10 Bjorken -(1+1)-HydroDynamics (BHD) Proper time  and rapidity y Phys.Rev.D27(1983)140 There is no dependence on Lorenz boost variable y: Landau hydrodynamical model, viscosity and conductivity are neglected

ITEP meeting S.Kiselev11 Photon spectrum in BHD Photon 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, T 0 and T f (at freeze-out) Connection with the local rest frame  Input function – production rate E dN/d 4 xd 3 p (E,T) Phys.Rep.364(2002)98

ITEP meeting S.Kiselev12 HHG scenario  C.Song, Phys.Rev.C47(1993)2861 an effective chiral Lagrangian with π, ρ and a 1 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

ITEP meeting S.Kiselev13 GeT_HHG: comparison with SPS and RHIC Choosing T 0 and  0 one can fit data in the hadron scenario comparison with data, T f = 100 MeV

ITEP meeting S.Kiselev14 GeT_HHG: prediction for LHC

ITEP meeting S.Kiselev15 GeT_HHG: sensitivity to the parameters sensitivity to T 0 sensitivity to T f

ITEP meeting S.Kiselev16 QGP scenario: QGP and HHG phases QGP: ideal massless parton gas (µ q =0)HHG: ideal massless pion gas First order phase transition at critical temperature T c B bag constant N c colors N f flavors g number of degrees of freedom

QGP scenario: mixed phase ITEP meeting S.Kiselev17 Mixed phase Main parameters: initial  0, T 0, T c and T f

Rates from QGP -1 st order ITEP meeting S.Kiselev18 Perturbative thermal QCD applying Hard thermal loop (HTL) resummation Phys.Lett.B510(2001)98

Rates from QGP -2 nd order ITEP meeting S.Kiselev19 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 α s One must consider the QGP rates as an educated guess

To do ITEP meeting S.Kiselev20 Write and test the macros GeT_QGP.C Think on the “hard+thermal” generator