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@forthommel
forthommel committed Apr 23, 2021
2 parents 81600b0 + 6c5c01d commit 3199bf0
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1,171 changes: 565 additions & 606 deletions CepGenProcesses/LPAIR.cpp
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248 changes: 121 additions & 127 deletions CepGenProcesses/LPAIR.h
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Expand Up @@ -3,10 +3,8 @@

#include "CepGen/Processes/Process.h"

namespace cepgen
{
namespace proc
{
namespace cepgen {
namespace proc {
/**
* Full class of methods and objects to compute the full analytic matrix element
* \cite Vermaseren:1982cz for the \f$\gamma\gamma\to\ell^{+}\ell^{-}\f$ process
Expand All @@ -30,24 +28,21 @@ namespace cepgen
* \brief Compute the matrix element for a CE \f$\gamma\gamma\to\ell^{+}\ell^{-}\f$
* process
*/
class LPAIR : public Process
{
public:
/// \brief Class constructor: set the mandatory parameters before integration and events generation
/// \param[in] params General process parameters (nopt = Optimisation, legacy from LPAIR)
explicit LPAIR( const ParametersList& params = ParametersList() );
ProcessPtr clone() const override {
return ProcessPtr( new LPAIR( *this ) );
}

void addEventContent() override;
double computeWeight() override;
void prepareKinematics() override;
void fillKinematics( bool ) override;
static std::string description() { return "ɣɣ → l⁺l¯ (LPAIR)"; }

private:
/**
class LPAIR : public Process {
public:
/// \brief Class constructor: set the mandatory parameters before integration and events generation
/// \param[in] params General process parameters (nopt = Optimisation, legacy from LPAIR)
explicit LPAIR(const ParametersList& params = ParametersList());
ProcessPtr clone() const override { return ProcessPtr(new LPAIR(*this)); }

void addEventContent() override;
double computeWeight() override;
void prepareKinematics() override;
void fillKinematics(bool) override;
static std::string description() { return "ɣɣ → l⁺l¯ (LPAIR)"; }

private:
/**
* Calculate energies and momenta of the
* 1st, 2nd (resp. the "proton-like" and the "electron-like" incoming particles),
* 3rd (the "proton-like" outgoing particle),
Expand All @@ -56,8 +51,8 @@ namespace cepgen
* \brief Energies/momenta computation for the various particles, in the CM system
* \return Success state of the operation
*/
bool orient();
/**
bool orient();
/**
* Compute the expression of the matrix element squared for the \f$\gamma\gamma\rightarrow\ell^{+}\ell^{-}\f$ process.
* It returns the value of the convolution of the form factor or structure functions with the central two-photons matrix element squared.
* \brief Computes the matrix element squared for the requested process
Expand All @@ -68,113 +63,112 @@ namespace cepgen
* b = t_1 t_2+\left(w_{\gamma\gamma}\sin^2{\theta^{\rm CM}_6}+4m_\ell\cos^2{\theta^{\rm CM}_6}\right) p_g^2
* \f]
*/
double periPP() const;
/**
double periPP() const;
/**
* Describe the kinematics of the process \f$p_1+p_2\to p_3+p_4+p_5\f$ in terms of Lorentz-invariant variables.
* These variables (along with others) will then be fed into the \a PeriPP method (thus are essential for the evaluation of the full matrix element).
* \return Success state of the operation
*/
bool pickin();

/// Internal switch for the optimised code version (LPAIR legacy ; unimplemented here)
const int n_opt_;
pdgid_t pair_;
const bool symmetrise_;

std::vector<double> x_tmp_;
double theta4_;
double phi6_cm_;
double x6_;

Limits w_limits_;
struct Masses
{
/// squared mass of the outgoing leptons
double Ml2 = 0.;
/// \f$\delta_2=m_1^2-m_2^2\f$ as defined in \cite Vermaseren:1982cz
double w12 = 0.;
/// \f$\delta_1=m_3^2-m_1^2\f$ as defined in \cite Vermaseren:1982cz
double w31 = 0.;
/// \f$\delta_4=m_5^2-m_2^2\f$ as defined in \cite Vermaseren:1982cz
double w52 = 0.;
} masses_;

/// energy of the first proton-like incoming particle
double ep1_;
/// energy of the second proton-like incoming particle
double ep2_;
double p_cm_;

/// energy of the two-photon central system
double ec4_;
/// 3-momentum norm of the two-photon central system
double pc4_;
/// mass of the two-photon central system
double mc4_;
/// squared mass of the two-photon central system
double w4_;

/// \f$p_{12} = \frac{1}{2}\left(s-m_{p_1}^2-m_{p_2}^2\right)\f$
double p12_;
double p1k2_, p2k1_;
/// \f$p_{13} = -\frac{1}{2}\left(t_1-m_{p_1}^2-m_{p_3}^2\right)\f$
double p13_;
double p14_, p25_;

double q1dq_, q1dq2_;

double s1_, s2_;

double epsi_;
double g5_, g6_;
double a5_, a6_;
double bb_;

double gram_;
double dd1_, dd2_, dd3_;
/// \f$\delta_5=m_4^2-t_1\f$ as defined in Vermaseren's paper
/// \cite Vermaseren:1982cz for the full definition of this quantity
double dd4_;
double dd5_;
/**
bool pickin();

/// Internal switch for the optimised code version (LPAIR legacy ; unimplemented here)
const int n_opt_;
pdgid_t pair_;
const bool symmetrise_;

std::vector<double> x_tmp_;
double theta4_;
double phi6_cm_;
double x6_;

Limits w_limits_;
struct Masses {
/// squared mass of the outgoing leptons
double Ml2 = 0.;
/// \f$\delta_2=m_1^2-m_2^2\f$ as defined in \cite Vermaseren:1982cz
double w12 = 0.;
/// \f$\delta_1=m_3^2-m_1^2\f$ as defined in \cite Vermaseren:1982cz
double w31 = 0.;
/// \f$\delta_4=m_5^2-m_2^2\f$ as defined in \cite Vermaseren:1982cz
double w52 = 0.;
} masses_;

/// energy of the first proton-like incoming particle
double ep1_;
/// energy of the second proton-like incoming particle
double ep2_;
double p_cm_;

/// energy of the two-photon central system
double ec4_;
/// 3-momentum norm of the two-photon central system
double pc4_;
/// mass of the two-photon central system
double mc4_;
/// squared mass of the two-photon central system
double w4_;

/// \f$p_{12} = \frac{1}{2}\left(s-m_{p_1}^2-m_{p_2}^2\right)\f$
double p12_;
double p1k2_, p2k1_;
/// \f$p_{13} = -\frac{1}{2}\left(t_1-m_{p_1}^2-m_{p_3}^2\right)\f$
double p13_;
double p14_, p25_;

double q1dq_, q1dq2_;

double s1_, s2_;

double epsi_;
double g5_, g6_;
double a5_, a6_;
double bb_;

double gram_;
double dd1_, dd2_, dd3_;
/// \f$\delta_5=m_4^2-t_1\f$ as defined in Vermaseren's paper
/// \cite Vermaseren:1982cz for the full definition of this quantity
double dd4_;
double dd5_;
/**
* Invariant used to tame divergences in the matrix element computation. It is defined as
* \f[\Delta = \left(p_1\cdot p_2\right)\left(q_1\cdot q_2\right)-\left(p_1\cdot q_2\right)\left(p_2\cdot q_1\right)\f]
* with \f$p_i, q_i\f$ the 4-momenta associated to the incoming proton-like particle and to the photon emitted from it.
*/
double delta_;
double g4_;
double sa1_, sa2_;

double sl1_;

/// cosine of the polar angle for the two-photons centre-of-mass system
double cos_theta4_;
/// sine of the polar angle for the two-photons centre-of-mass system
double sin_theta4_;

double al4_;
double be4_;
double de3_, de5_;
double pt4_;

/// Kinematics of the first incoming proton
Momentum p1_lab_;
/// Kinematics of the second incoming proton
Momentum p2_lab_;
/// Kinematics of the first outgoing proton
Momentum p3_lab_;
/// Kinematics of the two-photon system (in the two-proton CM)
Momentum p4_lab_;
/// Kinematics of the second outgoing proton
Momentum p5_lab_;
/// Kinematics of the first outgoing lepton (in the two-proton CM)
Momentum p6_cm_;
/// Kinematics of the second outgoing lepton (in the two-proton CM)
Momentum p7_cm_;
double jacobian_;

private:
/**
double delta_;
double g4_;
double sa1_, sa2_;

double sl1_;

/// cosine of the polar angle for the two-photons centre-of-mass system
double cos_theta4_;
/// sine of the polar angle for the two-photons centre-of-mass system
double sin_theta4_;

double al4_;
double be4_;
double de3_, de5_;
double pt4_;

/// Kinematics of the first incoming proton
Momentum p1_lab_;
/// Kinematics of the second incoming proton
Momentum p2_lab_;
/// Kinematics of the first outgoing proton
Momentum p3_lab_;
/// Kinematics of the two-photon system (in the two-proton CM)
Momentum p4_lab_;
/// Kinematics of the second outgoing proton
Momentum p5_lab_;
/// Kinematics of the first outgoing lepton (in the two-proton CM)
Momentum p6_cm_;
/// Kinematics of the second outgoing lepton (in the two-proton CM)
Momentum p7_cm_;
double jacobian_;

private:
/**
* Define modified variables of integration to avoid peaks integrations (see \cite Vermaseren:1982cz for details)
* Return a set of two modified variables of integration to maintain the stability of the integrand. These two new variables are :
* - \f$y_{out} = x_{min}\left(\frac{x_{max}}{x_{min}}\right)^{exp}\f$ the new variable
Expand All @@ -191,10 +185,10 @@ namespace cepgen
* - opposite sign :
* > `mapt1`, `mapt2`
*/
std::pair<double,double> map( double expo, const Limits& lim, const std::string& var_name = "" );
std::pair<double,double> mapla( double y, double z, int u, const Limits& lim );
std::pair<double, double> map(double expo, const Limits& lim, const std::string& var_name = "");
std::pair<double, double> mapla(double y, double z, int u, const Limits& lim);
};
}
}
} // namespace proc
} // namespace cepgen

#endif

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