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0001 #ifndef BEAM_Main_Laser_Backscattering_H 0002 #define BEAM_Main_Laser_Backscattering_H 0003 0004 #include "BEAM/Main/Beam_Base.H" 0005 0006 namespace BEAM { 0007 class Laser_Backscattering : public Beam_Base { 0008 double m_energyL,m_polarisationL; 0009 int m_mode; 0010 bool m_angles,m_pol; 0011 double m_Ebounds[2]; 0012 double m_rho2,m_delta; 0013 double m_nonlin1,m_nonlin2,m_xi; 0014 double m_xe, m_xmax, m_xmax2; 0015 double m_upper,m_peak; 0016 0017 double m_yfix,m_yden; 0018 int m_ysteps; 0019 0020 double m_totalC,m_total2,m_totalE; 0021 0022 double m_polar; 0023 0024 double Compton(double,double,double,double &); 0025 double TwoPhotons(double,double,double,double &); 0026 double Rescattering(double,double,double,double &); 0027 double SimpleCompton(double,double,double); 0028 double Polarisation(double,double,double,double); 0029 public: 0030 Laser_Backscattering(const ATOOLS::Flavour,const double,const double, 0031 const double,const double,const int,const int,const int,const int); 0032 ~Laser_Backscattering(); 0033 0034 Beam_Base * Copy(); 0035 void PrintSpectra(std::string,int=0); 0036 bool CalculateWeight(double,double); 0037 double Weight(ATOOLS::Flavour=ATOOLS::Flavour(kf_none)); 0038 ATOOLS::Vec4D OutMomentum(const size_t & i=0); 0039 0040 double Polarisation() { return m_polar; } 0041 void SetMode(int _mode) { m_mode = _mode; } 0042 void SetPol(bool on) { m_pol = on; } 0043 int Mode() { return m_mode; } 0044 bool Pol() { return m_pol; } 0045 double Exponent() { return 0.5; } 0046 double Xmax() { return m_upper; } 0047 double Peak() { return m_peak; } 0048 bool PolarisationOn() ; 0049 }; 0050 0051 0052 /*! 0053 \file 0054 \brief contains the class BEAM::Laser_Backscattering. 0055 */ 0056 /*! 0057 \class Laser_Backscattering 0058 \brief This class is for Laser back scattering off electrons. 0059 0060 In this class the 0061 <A HREF="http://131.169.91.193/cgi-bin/spiface/find/hep/www?rawcmd=FIND+eprint+hep-ex%2F0207021"> 0062 CompAZ</A> parametrization is implemented. This is a phenomenological parametrization, including 0063 three components, each of which is modified with some additional non linear terms. These 0064 components are: 0065 - Compton scattering, 0066 - Rescattering processes, i.e. interactions involving two electrons, and 0067 - Two photon processes. 0068 0069 They are all based on a simple Compton backscattering spectrum implemented in 0070 Laser_Backscattering::SimpleCompton(double,double,double). 0071 */ 0072 /*! 0073 \var int Laser_Backscattering::m_mode 0074 The mode for the CompAZ spectrum: 0075 - 0 all contributions. 0076 - 1 direct contribution of Compton process only. 0077 - 2 scattering with 2 photons only. 0078 - 3 scattering off secondary electrons. 0079 . 0080 another option is to use just the simple compton spectrum 0081 - -1 for comparison only. 0082 . 0083 */ 0084 /*! 0085 \var bool Laser_Backscattering::m_angles 0086 Collinear photons (0) or angles taken into account (1). At the moment only option 0, 0087 i.e. collinear photons, is supported. 0088 0089 \todo Enable m_angles = 1. 0090 */ 0091 /*! 0092 \var bool Laser_Backscattering::m_pol 0093 Whether degree of polarization should be calculated or not. This happens, if the incoming 0094 electron beam has a polarization degree different from 0 or if the Laser photons are polarized. 0095 */ 0096 /*! 0097 \var double Laser_Backscattering::m_Ebounds[2] 0098 The electron energies bounds for this parametrization to be resaonable. 0099 At the moment they are set to 50 GeV < E < 500 GeV. 0100 */ 0101 /*! 0102 \var double Laser_Backscattering::m_energyL 0103 The energy of the laser-photons, \f$\omega_L\f$. 0104 */ 0105 /*! 0106 \var double Laser_Backscattering::m_polarisationL 0107 The polarization degree of the laser-photons, \f$\lambda_L\f$. 0108 */ 0109 /*! 0110 \var double Laser_Backscattering::m_xe 0111 The characteristic parameter of the process, given by: 0112 \f[ 0113 \xi = \frac{4E_e\omega_L}{m_e^2}\,. 0114 \f] 0115 If nonlinear corrections are included, this is modified to read 0116 \f[ 0117 \xi = \frac{4E_e\omega_L}{m_e^2(1+\chi)}\,. 0118 \f] 0119 */ 0120 /*! 0121 \var double Laser_Backscattering::m_xmax 0122 The maximal energy fraction \f$ x_{\rm max}\f$ the backscattered photons can obtain from Compton 0123 scattering. It is given by 0124 \f[ 0125 x_{\rm max} = \frac{\xi}{1+\xi} 0126 \f] 0127 */ 0128 /*! 0129 \var double Laser_Backscattering::m_xmax2 0130 The maximal energy fraction for backscattered photons from the two photon process, 0131 \f$ x_{\rm max}^{(2)}\f$. 0132 It is given by 0133 \f[ 0134 x_{\rm max}^{(2)} = \frac{2\xi}{1+2\xi}\,. 0135 \f] 0136 */ 0137 /*! 0138 \var double Laser_Backscattering::m_rho2 0139 A parameter for the damping of the Compton pieces of the spectrum, \f$\rho^2\f$. 0140 */ 0141 /*! 0142 \var double Laser_Backscattering::m_delta 0143 A parameter for the damping of the two photon piece of the spectrum, \f$\delta\f$. 0144 */ 0145 /*! 0146 \var double Laser_Backscattering::m_nonlin1 0147 Parameter for nonlinear corrections \f$\nu_1\f$. 0148 */ 0149 /*! 0150 \var double Laser_Backscattering::m_nonlin2 0151 Parameter for nonlinear corrections \f$\nu_2\f$. 0152 */ 0153 /*! 0154 \var double Laser_Backscattering::m_xi 0155 The effective nonlinearity parameter \f$\chi\f$. It is given by 0156 \f[ 0157 \chi = \nu_1 + \nu_2 E_e\,. 0158 \f] 0159 */ 0160 /*! 0161 \var double Laser_Backscattering::m_upper 0162 Depending on the mode, this is either \f$ x_{\rm max}\f$ or \f$ x_{\rm max}^{(2)}\f$. 0163 */ 0164 /*! 0165 \var double Laser_Backscattering::m_peak 0166 The peak position of the spectrum, \f$ x_{\rm max}\f$. 0167 */ 0168 /*! 0169 \var double Laser_Backscattering::m_yfix 0170 A parameter for the evaluation of the rescattering-convolution, \f$y_{\rm fix} = 1/(1-\xi)\f$. 0171 */ 0172 /*! 0173 \var double Laser_Backscattering::m_yden 0174 A parameter for the evaluation of the rescattering-convolution, \f$y_{\rm den} = \log(1-\xi)\f$. 0175 */ 0176 /*! 0177 \var int Laser_Backscattering::m_ysteps 0178 The number of steps in the convolution for the rescattering. 0179 */ 0180 /*! 0181 \var double Laser_Backscattering::m_totalC 0182 The norm of the Compton contribution. 0183 */ 0184 /*! 0185 \var double Laser_Backscattering::m_total2 0186 The norm of the two-photon contribution. 0187 */ 0188 /*! 0189 \var double Laser_Backscattering::m_totalE 0190 The norm of the rescatering contribution. 0191 */ 0192 /*! 0193 \var double Laser_Backscattering::m_polar 0194 The polarization degree. 0195 */ 0196 /*! 0197 \fn Laser_Backscattering::Laser_Backscattering(const ATOOLS::Flavour,const double,const double, 0198 const double,const double,const int, 0199 const int,const int,bool &); 0200 This is the constructor of the class. It initializes a large variety of internal parameters. 0201 The vectors are constructed by calling the default constructor of the Beam_Base. 0202 */ 0203 /*! 0204 \fn Beam_Base * Laser_Backscattering::Copy() 0205 A method to fully copy the class, including all parameter settings. 0206 */ 0207 /*! 0208 \fn void Laser_Backscattering::PrintSpectra(std::string) 0209 When called, this method outputs the spectra and its contributions to a file specified by 0210 the string variable. 0211 */ 0212 /*! 0213 \fn bool Laser_Backscattering::CalculateWeight(double,double); 0214 Calculates the weight dependent on hte energy fraction \f$x\f$ of the photon w.r.t the 0215 incoming lepton and in accordance with the mode given by Laser_Backscattering::m_mode. 0216 */ 0217 /*! 0218 \fn double Laser_Backscattering::Weight(ATOOLS::Flavour=ATOOLS::Flavour(kf_none)); 0219 After checking that the outgoing particle indeed is a photon, the calculated weight 0220 is returned. In principle, from there one could also return an electron energy distribution, 0221 but this has not been implmeneted yet. 0222 */ 0223 /*! 0224 \fn double Laser_Backscattering::SimpleCompton(double,double,double). 0225 Evaluates and returns the normalized simple Compton backscattering spectrum 0226 \f[ 0227 {\cal F}_C(x,z,\Lambda) = \frac{1}{{\cal N}(z,\Lambda)}\times 0228 \left[1-x + \frac{1}{1-x} - \frac{4z}{1+z} + \frac{4z^2}{(1+z)^2} 0229 -\Lambda \frac{2x-x^2}{1-x}\cdot\left(\frac{2z}{1+z}-1\right)\right]\,, 0230 \f] 0231 where the norm reads 0232 \f[ 0233 {\cal N}_C(z,\Lambda) = \frac{z^3+18z^2+32z+16}{2z(1+z)^2} 0234 +\frac{z^2-4z-8}{z^2}\log(1+z) 0235 -\Lambda\left[2+\frac{z^2}{(1+z)^2}-\frac{2+z}{z}\log(1+z)\right]\,, 0236 \f] 0237 for \f$ x\in [0,z]\f$. In most theory papers this form alone is used, then \f$ z = \xi\f$. 0238 */ 0239 /*! 0240 \var double Laser_Backscattering::Compton(double,double,double,double &) 0241 This is the - eventually modified - Compton piece of the spectrum. It is given 0242 by the simple Compton piece above and some corrections and reads 0243 \f[ 0244 {\cal F}_1(x,\lambda_e,\lambda_L,{\cal P}) = \frac{1}{{\cal N}_1}\cdot 0245 \exp\left[-\frac{\rho^2}{8}\left(\frac{\xi}{x}-\xi-1\right)\right] 0246 \cdot {\cal F}_C(x,\xi,\lambda_e\cdot\lambda_L)\,. 0247 \f] 0248 The range for \f$ x\f$ is \f$ x\in [0,x_{\rm max}]\f$. 0249 */ 0250 /*! 0251 \var double Laser_Backscattering::TwoPhotons(double,double,double,double &) 0252 This is the - eventually modified - two photon piece of the spectrum. It is given 0253 by the simple Compton piece above and some corrections and reads 0254 \f[ 0255 {\cal F}_2(x,\lambda_e,\lambda_L,{\cal P}) = \frac{1}{{\cal N}_2}\cdot 0256 \exp\left[-\frac{\rho^2}{8}\left(\frac{2\xi}{x}-2\xi-1\right)\right] 0257 \cdot \left(\frac{2\xi}{x}-2\xi-1\right)^\delta 0258 \cdot {\cal F}_C(x,2\xi,\lambda_e\cdot\lambda_L)\,. 0259 \f] 0260 The range for \f$ x\f$ is \f$ x\in [0,x_{\rm max}^{(2)}]\f$. 0261 */ 0262 /*! 0263 \var double Laser_Backscattering::Rescattering(double,double,double,double &) 0264 For the rescattering piece of the spectrum a convolution of two simple Compton 0265 spectra has to be performed. 0266 The range for \f$ x\f$ is \f$ x\in [0,x_{\rm max}]\f$. 0267 */ 0268 /*! 0269 \var double Laser_Backscattering::Polarisation(double,double,double,double) 0270 The polarization piece of the spectrum yielding the degree of polarization for the outgoing 0271 photon. It is given by 0272 \f[ 0273 {\cal P}_C(x,z,\lambda_e,\lambda_L) = \frac{1}{\cal N}_P 0274 \lambda_e \left[\frac{x}{1-x}\left(1+(1-x)\sqrt{\frac{2x}{z(1-x)}-1}\right)\right] - 0275 \lambda_L \left[\left(1-x+\frac{1}{1-x}\right)\left(\frac{2x}{z(1-x)}-1\right)\right]\,, 0276 \f] 0277 where the norm is given by 0278 \f[ 0279 {\cal N}_P = 1-x+\frac{1}{1-x}+\frac{4x}{z(1-x)}\left(\frac{x}{z(1-x)}-1\right) 0280 -\lambda_e\lambda_L\frac{x(2-x)}{1-x}\left(\frac{2x}{z(1-x)}-1\right)\,. 0281 \f] 0282 This expression is valid only for 0283 \f[ 0284 x \in \left[0,\frac{z}{1+z}\right]\,. 0285 \f] 0286 */ 0287 } 0288 0289 0290 #endif
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