LinearBreitWheeler.h

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#ifndef OPAL_LINEAR_BREIT_WHEELER_HH
#define OPAL_LINEAR_BREIT_WHEELER_HH
 
#include "OPALTypes.h"
 
#include <cstdint>
#include <random>
 
namespace Physics {
    namespace LinearBreitWheeler {
 
        struct SamplingKernel {
            double highEnergyPhotonEnergyGeV =
                    0.0;  
            double laserPhotonEnergyGeV =
                    0.0;  
            Vector_t<double, 3> highEnergyDirection = Vector_t<double, 3>(
                    0.0);  
            Vector_t<double, 3> laserDirection =
                    Vector_t<double, 3>(0.0);  
            double invariantSGeV2 = 0.0;       
            double pairBetaCM = 0.0;  
            double cmLorentzGamma =
                    0.0;  
            Vector_t<double, 3> cmVelocity =
                    Vector_t<double, 3>(0.0);  
            double rejectionUpperBound = 0.0;  
        };
 
        struct SampledEvent {
            double scatteringCosineCM =
                    0.0;             
            double azimuthCM = 0.0;  
            double electronEnergyLabGeV =
                    0.0;  
            double positronEnergyLabGeV =
                    0.0;  
            Vector_t<double, 3> electronMomentumLabGeV = Vector_t<double, 3>(
                    0.0);  
            Vector_t<double, 3> positronMomentumLabGeV = Vector_t<double, 3>(
                    0.0);  
        };
 
        double photonEnergyFromWavelengthGeV(double wavelength_m);
 
        double invariantSGeV2(
                double photon1EnergyGeV, double photon2EnergyGeV,
                const Vector_t<double, 3>& photon1Direction,
                const Vector_t<double, 3>& photon2Direction);
 
        double thresholdInvariantSGeV2();
 
        bool isAboveThreshold(double invariantSGeV2);
 
        double pairBetaCM(double invariantSGeV2);
 
        double totalCrossSection(double invariantSGeV2);
 
        double proposalZToScatteringCosineCM(double invariantSGeV2, double proposalZ);
 
        double unpolarizedAngularWeight(double invariantSGeV2, double proposalZ);
 
        SamplingKernel makeSamplingKernel(
                double highEnergyPhotonEnergyGeV, double laserPhotonEnergyGeV,
                const Vector_t<double, 3>& highEnergyDirection,
                const Vector_t<double, 3>& laserDirection);
 
        std::mt19937_64 makeHostRandomEngine(std::uint64_t streamIndex = 0);
 
        SampledEvent sampleEvent(const SamplingKernel& kernel, std::mt19937_64& engine);
 
    }  // namespace LinearBreitWheeler
}  // namespace Physics
 
#endif  // OPAL_LINEAR_BREIT_WHEELER_HH