Photon Production in High-Energy Collisions: Direct and Prompt Processes

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 ITEP meeting S.Kiselev

2. Introduction ITEP meeting S.Kiselev

3. 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.Kiselev

4. 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 ~ 50-100 fm) π0 γγ,   γγ, ’ργ/ωγ/2γ • Shot lived (ccAB ~ 50-100 fm) ω  πγ, a1  πγ, Δ Nγ, K* Kγ,   γ, ρ ππγ, . . . ITEP meeting S.Kiselev

5. Introduction – SPS data ITEP meeting S.Kiselev

6. Introduction – RHIC data ITEP meeting S.Kiselev

7. Hard scattered parton interacts with gluon in bulk matter Introduction - new processes at RHIC Photons in A+A Decay Photons Direct Photons jet-g-conv. hard Preequilibriumphotons ??? thermal hard+thermal `direct` fragmentation QGP Hadron gas Medium inducedg bremsstr. ITEP meeting S.Kiselev

8. 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 ITEP meeting S.Kiselev

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

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

11. Phys.Rep.364(2002)98 Photon spectrum in BHD Photon spectra follow from convoluting the photon productionrates with the space–time evolutionof thecollision For a longitudinallyexpanding cylinder For proper time  and rapidity y` Input function – production rate E dN/d4xd3p (E,T) Connection with the local rest frame For anidealgas  Main parameters: initial 0 , T0 and Tf (at freeze-out) ITEP meeting S.Kiselev

12. HHG scenario • C.Song, Phys.Rev.C47(1993)2861 an effective chiral Lagrangian with π, ρanda1 mesons to calculate theprocesses 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.Kiselev

13. GeT_HHG: comparison with SPS and RHIC comparison with data, Tf = 100 MeV Choosing T0 and 0 one can fit data in the hadron scenario ITEP meeting S.Kiselev

14. GeT_HHG: prediction for LHC ITEP meeting S.Kiselev

15. GeT_HHG: sensitivity to the parameters sensitivity to T0 sensitivityto Tf ITEP meeting S.Kiselev

16. QGP scenario: QGP and HHG phases QGP: ideal massless parton gas (µq =0) HHG: ideal massless pion gas B bag constant g number of degrees of freedom Nc colors Nf flavors First order phase transition at critical temperature Tc ITEP meeting S.Kiselev

17. QGP scenario: mixed phase Mixed phase Main parameters: initial 0 , T0 , Tc and Tf ITEP meeting S.Kiselev

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

19. Rates from QGP -2nd order 2-loop contribution is the same order in αs Thermal photon production in the QGP is a non-perturbative mechanism that can not be accessed in perturbative HTL resummed thermal field theory One must consider the QGP rates as an educated guess ITEP meeting S.Kiselev

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