EIC code displayed by LXR |
|
|
|
|||
File indexing completed on 2025-09-17 08:53:33
0001 //------------------------------- -*- C++ -*- -------------------------------// 0002 // Copyright Celeritas contributors: see top-level COPYRIGHT file for details 0003 // SPDX-License-Identifier: (Apache-2.0 OR MIT) 0004 //---------------------------------------------------------------------------// 0005 //! \file celeritas/em/distribution/MuAngularDistribution.hh 0006 //---------------------------------------------------------------------------// 0007 #pragma once 0008 0009 #include "corecel/Macros.hh" 0010 #include "corecel/Types.hh" 0011 #include "corecel/math/Algorithms.hh" 0012 #include "corecel/random/distribution/UniformRealDistribution.hh" 0013 #include "celeritas/Constants.hh" 0014 #include "celeritas/Quantities.hh" 0015 0016 namespace celeritas 0017 { 0018 //---------------------------------------------------------------------------// 0019 /*! 0020 * Sample the polar angle for muon bremsstrahlung and pair production. 0021 * 0022 * The polar angle is sampled according to a simplified PDF 0023 * \f[ 0024 f(r) \sim \frac{r}{(1 + r^2)^2}, \ r = frac{E\theta}{m} 0025 * \f] 0026 * by sampling 0027 * \f[ 0028 \theta = r\frac{m}{E} 0029 * \f] 0030 * with 0031 * \f[ 0032 r = \sqrt{frac{a}{1 - a}}, 0033 a = \xi \frac{r^2_{\text{max}}}{1 + r^2_{\text{max}}}, 0034 r_{\text{max}} = frac{\pi}{2} E' / m \min(1, E' / \epsilon), 0035 * \f] 0036 * and where \f$ m \f$ is the incident muon mass, \f$ E \f$ is incident energy, 0037 * \f$ \epsilon \f$ is the emitted energy, 0038 * \f$ E' = E - \epsilon \f$, and \f$ \xi \sim U(0,1) \f$. 0039 * 0040 * \note This performs the same sampling routine as in Geant4's \c 0041 * G4ModifiedMephi class and documented in section 11.2.4 of the Geant4 Physics 0042 * Reference (release 11.2). 0043 */ 0044 class MuAngularDistribution 0045 { 0046 public: 0047 //!@{ 0048 //! \name Type aliases 0049 using Energy = units::MevEnergy; 0050 using Mass = units::MevMass; 0051 //!@} 0052 0053 public: 0054 // Construct with incident and secondary particle quantities 0055 inline CELER_FUNCTION 0056 MuAngularDistribution(Energy inc_energy, Mass inc_mass, Energy energy); 0057 0058 // Sample the cosine of the polar angle of the secondary 0059 template<class Engine> 0060 inline CELER_FUNCTION real_type operator()(Engine& rng); 0061 0062 private: 0063 // Incident particle Lorentz factor 0064 real_type gamma_; 0065 // r_max^2 / (1 + r_max^2) 0066 UniformRealDistribution<real_type> sample_a_; 0067 }; 0068 0069 //---------------------------------------------------------------------------// 0070 // INLINE DEFINITIONS 0071 //---------------------------------------------------------------------------// 0072 /*! 0073 * Construct with incident and secondary particle. 0074 */ 0075 CELER_FUNCTION 0076 MuAngularDistribution::MuAngularDistribution(Energy inc_energy, 0077 Mass inc_mass, 0078 Energy energy) 0079 : gamma_(1 + value_as<Energy>(inc_energy) / value_as<Mass>(inc_mass)) 0080 { 0081 real_type r_max_sq = ipow<2>( 0082 real_type(0.5) * constants::pi * gamma_ 0083 * min(real_type(1), 0084 gamma_ * value_as<Mass>(inc_mass) / value_as<Energy>(energy) - 1)); 0085 sample_a_ = {0, r_max_sq / (1 + r_max_sq)}; 0086 } 0087 0088 //---------------------------------------------------------------------------// 0089 /*! 0090 * Sample the cosine of the polar angle of the secondary. 0091 */ 0092 template<class Engine> 0093 CELER_FUNCTION real_type MuAngularDistribution::operator()(Engine& rng) 0094 { 0095 real_type a = sample_a_(rng); 0096 return std::cos(std::sqrt(a / (1 - a)) / gamma_); 0097 } 0098 0099 //---------------------------------------------------------------------------// 0100 } // namespace celeritas
| [ Source navigation ] | [ Diff markup ] | [ Identifier search ] | [ general search ] |
|
This page was automatically generated by the 2.3.7 LXR engine. The LXR team |
|