da/d1f/BetheBloch_8hpp_source.html

// This file is part of the Acts project.

//

// Copyright (C) 2018-2020 CERN for the benefit of the Acts project

//

// This Source Code Form is subject to the terms of the Mozilla Public

// License, v. 2.0. If a copy of the MPL was not distributed with this

// file, You can obtain one at http://mozilla.org/MPL/2.0/.


#pragma once


#include "Acts/Material/Interactions.hpp"

#include "Acts/Material/MaterialSlab.hpp"

#include "ActsFatras/EventData/Particle.hpp"

#include "ActsFatras/Utilities/LandauDistribution.hpp"


#include <array>


namespace ActsFatras {


struct BetheBloch {

  double scaleFactorMPV = 1.;

  double scaleFactorSigma = 1.;


  template <typename generator_t>

  std::array<Particle, 0> operator()(generator_t &generator,

                                     const Acts::MaterialSlab &slab,

                                     Particle &particle) const {

    // compute energy loss distribution parameters

    const auto pdg = particle.pdg();

    const auto m = particle.mass();

    const auto qOverP = particle.charge() / particle.absMomentum();

    const auto q = particle.charge();

    // most probable value

    const auto energyLoss =

        Acts::computeEnergyLossLandau(slab, pdg, m, qOverP, q);

    // Gaussian-equivalent sigma

    const auto energyLossSigma =

        Acts::computeEnergyLossLandauSigma(slab, pdg, m, qOverP, q);


    // Simulate the energy loss

    // TODO landau location and scale parameters are not identical to the most

    //      probable value and the Gaussian-equivalent sigma

    LandauDistribution lossDistribution(scaleFactorMPV * energyLoss,

                                        scaleFactorSigma * energyLossSigma);

    const auto loss = lossDistribution(generator);


    // Apply the energy loss

    particle.correctEnergy(-loss);


    // Generates no new particles

    return {};

  }

};


}  // namespace ActsFatras