fast generators of direct photons

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

Introduction



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.


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, . . .

Introduction – SPS data


Introduction – RHIC data



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


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


Generator of Prompt Photons (GePP): results

Comparison with RHIC data Prediction for LHC


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


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


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


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


GeT_HHG: prediction for LHC


GeT_HHG: sensitivity to the parameters

sensitivity to T0 sensitivity to Tf


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

QGP scenario: mixed phase


Mixed phase

Main parameters: initial 0 , T0 , Tc and Tf

Rates from QGP -1st order


Perturbative thermal QCD applyingHard thermal loop (HTL) resummation

Phys.Lett.B510(2001)98

Rates from QGP -2nd order


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

To do


• Write and test the macros GeT_QGP.C• Think on the “hard+thermal” generator

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