class AliGenPromptPhotons: public AliGenerator

 Default constructor

 Standard constructor

 Standard destructor

 Initialisation

 Generate thermal photons of a event

 input:
 x[0] - p_t (GeV).
 par[0]=sqrt(s_NN) (GeV),

 output:
 d^{2}#sigma/(dp_t dy) (pb/GeV)


 d^{2}#sigma/(dp_t dy) = (2 pi p_t) Ed^{3}#sigma/d^{3}p

 data presentation: Nucl.Phys.A783:577-582,2007, hep-ex/0609037, fig.3
 F(x_t)=(#sqrt{s})^{5} Ed^{3}#sigma/d^{3}p

 approximate tabulation of F(x_t)

 input:
 x[0] - r (fm)
 par[0] - R (fm), radius
 par[1] - d (fm), surface thickness

 output:
 4 pi r**2 /(1+exp((r-R)/d))

 Wood Saxon (WS) C/(1+exp((r-RA)/d)) (nuclons/fm^3)
 To get the normalization A = (Integral 4 pi r**2 dr WS):
 C = A / (Integral 4 pi r**2 dr 1/(1+exp((r-RA)/d)) )
 Thus me need 4 pi r**2 /(1+exp((r-RA)/d)) (1/fm)

 input:
 x[0] - z (fm)
 par[0] - R (fm), radius
 par[1] - d (fm), surface thickness
 par[2] - C (nucleons/fm**2), normalization factor
 par[3] - b (fm), impact parameter

 output:
  Wood Saxon Parameterisation
  as a function of z for fixed b (1/fm^3)

 input:
 x[0] - b (fm), impact parameter
 par[0] - RAMAX (fm), max. value of projectile radius

 output:
 nuclear thickness function T_A(b) (1/fm^2)

 input:
 x[0] - phi (rad)
 par[0] - RBMAX (fm), max. value of target radius
 par[1] - b (fm), impact parameter
 par[2] - s (fm)

 output:
  nuclear thickness function T_B(phi)=T_B(sqtr(s**2+b**2-2*s*b*cos(phi)))

 input:
 x[0] - s (fm)
 par[0] - RBMAX (fm), max. value of target radius
 par[1] - b (fm), impact parameter

 output:
  s * TA(s) * 2 * Integral(0,phiMax) TB(phi(s,b))

 input:
 x[0] - b (fm), impact parameter
 par[0] - RAMAX (fm), max. value of projectile radius
 par[1] - RAMAX (fm), max. value of target radius

 output:
 overlap function TAB(b) (1/fm**2)

 Setters