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BetheBloch.hpp
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1 // This file is part of the Acts project.
2 //
3 // Copyright (C) 2018-2020 CERN for the benefit of the Acts project
4 //
5 // This Source Code Form is subject to the terms of the Mozilla Public
6 // License, v. 2.0. If a copy of the MPL was not distributed with this
7 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
8 
9 #pragma once
10 
11 #include <array>
12 
17 
18 namespace ActsFatras {
19 
25 struct BetheBloch {
27  double scaleFactorMPV = 1.;
29  double scaleFactorSigma = 1.;
30 
39  template <typename generator_t>
40  std::array<Particle, 0> operator()(generator_t &generator,
41  const Acts::MaterialProperties &slab,
42  Particle &particle) const {
43  // compute energy loss distribution parameters
44  const auto pdg = particle.pdg();
45  const auto m = particle.mass();
46  const auto qOverP = particle.charge() / particle.absMomentum();
47  const auto q = particle.charge();
48  // most probable value
49  const auto energyLoss =
50  Acts::computeEnergyLossLandau(slab, pdg, m, qOverP, q);
51  // Gaussian-equivalent sigma
52  const auto energyLossSigma =
53  Acts::computeEnergyLossLandauSigma(slab, pdg, m, qOverP, q);
54 
55  // Simulate the energy loss
56  // TODO landau location and scale parameters are not identical to the most
57  // probable value and the Gaussian-equivalent sigma
58  LandauDistribution lossDistribution(scaleFactorMPV * energyLoss,
59  scaleFactorSigma * energyLossSigma);
60  const auto loss = lossDistribution(generator);
61 
62  // Apply the energy loss
63  particle.correctEnergy(-loss);
64 
65  // Generates no new particles
66  return {};
67  }
68 };
69 
70 } // namespace ActsFatras