ActsExamples/Utilities/ParametricParticleGenerator.hpp

0001 // This file is part of the ACTS project.
0002 //
0003 // Copyright (C) 2016 CERN for the benefit of the ACTS project
0004 //
0005 // This Source Code Form is subject to the terms of the Mozilla Public
0006 // License, v. 2.0. If a copy of the MPL was not distributed with this
0007 // file, You can obtain one at https://mozilla.org/MPL/2.0/.
0008
0009 #pragma once
0010
0011 #include "Acts/Definitions/PdgParticle.hpp"
0012 #include "Acts/Definitions/Units.hpp"
0013 #include "ActsExamples/Framework/RandomNumbers.hpp"
0014
0015 #include <array>
0016 #include <cstddef>
0017 #include <functional>
0018 #include <limits>
0019 #include <memory>
0020 #include <numbers>
0021 #include <optional>
0022 #include <random>
0023
0024 namespace HepMC3 {
0025 class GenEvent;
0026 }
0027
0028 namespace ActsExamples {
0029
0030 /// @brief Generator interface for vertices and particles
0031 struct ParticlesGenerator {
0032   /// @brief Virtual destructor required
0033   virtual ~ParticlesGenerator() = default;
0034   /// @brief Generate vertices and particles for one interaction
0035   /// @note This method cannot be `const` because the Pythia8 generator
0036   ///       uses the Pythia8 interfaces, which is non-const
0037   ///
0038   /// @param rng Shared random number generator instance
0039   /// @return The vertex and particle containers
0040   virtual std::shared_ptr<HepMC3::GenEvent> operator()(RandomEngine& rng) = 0;
0041 };
0042
0043 /// Generate particles from uniform parameter distributions.
0044 ///
0045 /// Generates a single vertex with the given number of tracks. The track
0046 /// direction is drawn from a uniform distribution on the unit sphere (within
0047 /// the given limits). Its absolute momentum is drawn from a uniform
0048 /// distribution. Position and time are always set to zero.
0049 class ParametricParticleGenerator : public ParticlesGenerator {
0050  public:
0051   struct Config {
0052     /// Low, high (exclusive) for the transverse direction angle.
0053     double phiMin = -std::numbers::pi;
0054     double phiMax = std::numbers::pi;
0055     /// Low, high (inclusive) for  the longitudinal direction angle.
0056     ///
0057     /// This intentionally uses theta instead of eta so it can represent the
0058     /// full direction space with finite values.
0059     ///
0060     /// @note This is the standard generation, for detector performance
0061     /// classification, where a flat distribution in eta can be useful,
0062     /// this can be set by the etaUniform flag;
0063     ///
0064     double thetaMin = std::numeric_limits<double>::min();
0065     double thetaMax = std::numbers::pi - std::numeric_limits<double>::epsilon();
0066     bool etaUniform = false;
0067     /// Low, high (exclusive) for absolute/transverse momentum.
0068     double pMin = 1 * Acts::UnitConstants::GeV;
0069     double pMax = 10 * Acts::UnitConstants::GeV;
0070     /// Indicate if the momentum refers to transverse momentum.
0071     bool pTransverse = false;
0072     /// Indicate if the momentum should be uniformly distributed in log space.
0073     bool pLogUniform = false;
0074     /// (Absolute) PDG particle number to identify the particle type.
0075     Acts::PdgParticle pdg = Acts::PdgParticle::eMuon;
0076     /// Randomize the charge and flip the PDG particle number sign accordingly.
0077     bool randomizeCharge = false;
0078     /// Number of particles.
0079     std::size_t numParticles = 1;
0080
0081     /// Overrides particle charge.
0082     std::optional<double> charge;
0083     /// Overrides particle mass.
0084     std::optional<double> mass;
0085   };
0086
0087   explicit ParametricParticleGenerator(const Config& cfg);
0088
0089   /// Generate a single primary vertex with the given number of particles.
0090   std::shared_ptr<HepMC3::GenEvent> operator()(RandomEngine& rng) override;
0091
0092  private:
0093   using UniformIndex = std::uniform_int_distribution<std::uint8_t>;
0094   using UniformReal = std::uniform_real_distribution<double>;
0095
0096   Config m_cfg;
0097
0098   // will be automatically set from PDG data tables
0099   double m_mass{};
0100
0101   // (anti-)particle choice is one random draw but defines two properties
0102   std::array<Acts::PdgParticle, 2> m_pdgChoices{};
0103
0104   UniformIndex m_particleTypeChoice;
0105   UniformReal m_phiDist;
0106   std::function<std::pair<double, double>(RandomEngine& rng)> m_sinCosThetaDist;
0107   std::function<double(RandomEngine& rng)> m_somePDist;
0108 };
0109
0110 }  // namespace ActsExamples