class AliGenThermalPhotons: public AliGenerator

 author: Sergey Kiselev, ITEP, Moscow
 e-mail: Sergey.Kiselev@cern.ch
 tel.: 007 495 129 95 45

 Generator of direct thermal photons for the reaction A+B, sqrt(S)
 main assumptions:
 1+1 Bjorken scaling hydrodinamics.
 1st order phase transition
 QGP + Mixed (QGP+HHG) + HHG (Hot Hadron Gas) phases,
 an ideal massless parton gas and ideal massless HHG
 see
 F.D.Steffen, nucl-th/9909035
 F.D.Steffen and M.H.Thoma, Phys.Lett. B510, 98 (2001)
 T.Peitzmann and M.H.Thoma, Phys.Rep., 364, 175 (2002)

 photon rates for QGP: Phys.Rep., 364, 175 (2002), section 2.1.1

 photon rates for HHG
 prates for i rho --> pi gamma, pi pi --> rho gamma and rho --> pi pi gamma:
 Song and Fai, Phys.Rev. C58, 1689 (1998)
 rates for omega --> pi gamma: Phys.Rev. D44, 2774 (1991)

 input parameters:
       fAProjectile, fATarget - number of nucleons in a nucleus A and B
       fMinImpactParam - minimal impct parameter, fm
       fMaxImpactParam - maximal impct parameter, fm
       fEnergyCMS - sqrt(S) per nucleon pair, AGeV
       fTau0 - initial proper time, fm/c
       fT0 - initial temperature, GeV
       fTc - critical temperature, GeV
       fTf - freeze-out temperature, GeV
       fGhhg - effective number of degrees of freedom in HHG

       fYMin - minimal rapidity of photons
       fYMax - maximal rapidity of photons
              in [fYMin,fYMax] uniform distribution of gamma is assumed
       fPtMin - minimal p_t value of gamma, GeV/c
       fPtMax - maximal p_t value of gamma, GeV/c

 comparison with SPS and RHIC data, prediction for LHC can be found in
 arXiv:0811.2634 [nucl-th]