PointwiseMaterialInteraction.hpp

Go to the documentation of this file. Or view the newest version in sPHENIX GitHub for file PointwiseMaterialInteraction.hpp

// This file is part of the Acts project.
//
// Copyright (C) 2019 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/Definitions/Algebra.hpp"
#include "Acts/Definitions/Common.hpp"
#include "Acts/Definitions/Direction.hpp"
#include "Acts/Definitions/PdgParticle.hpp"
#include "Acts/Definitions/TrackParametrization.hpp"
#include "Acts/Definitions/Units.hpp"
#include "Acts/Material/ISurfaceMaterial.hpp"
#include "Acts/Material/MaterialSlab.hpp"
#include "Acts/Surfaces/Surface.hpp"

#include <algorithm>
#include <cmath>

namespace Acts {
namespace detail {

struct PointwiseMaterialInteraction {
  const Surface* surface = nullptr;

  const Vector3 pos = Vector3(0., 0., 0);
  const double time = 0.0;
  const Vector3 dir = Vector3(0., 0., 0);
  const float qOverP = 0.0;
  const float absQ = 0.0;
  const float momentum = 0.0;
  const float mass = 0.0;
  const PdgParticle absPdg = PdgParticle::eInvalid;
  const bool performCovarianceTransport = false;
  const Direction navDir;

  MaterialSlab slab;
  double pathCorrection = 0.;
  double variancePhi = 0.;
  double varianceTheta = 0.;
  double varianceQoverP = 0.;
  double Eloss = 0.;
  double nextP = 0.;

  template <typename propagator_state_t, typename stepper_t>
  PointwiseMaterialInteraction(const Surface* sSurface,
                               const propagator_state_t& state,
                               const stepper_t& stepper)
      : surface(sSurface),
        pos(stepper.position(state.stepping)),
        time(stepper.time(state.stepping)),
        dir(stepper.direction(state.stepping)),
        qOverP(stepper.qOverP(state.stepping)),
        absQ(stepper.particleHypothesis(state.stepping).absoluteCharge()),
        momentum(stepper.absoluteMomentum(state.stepping)),
        mass(stepper.particleHypothesis(state.stepping).mass()),
        absPdg(stepper.particleHypothesis(state.stepping).absolutePdg()),
        performCovarianceTransport(state.stepping.covTransport),
        navDir(state.options.direction) {}

  template <typename propagator_state_t, typename navigator_t>
  bool evaluateMaterialSlab(
      const propagator_state_t& state, const navigator_t& navigator,
      MaterialUpdateStage updateStage = MaterialUpdateStage::FullUpdate) {
    // We are at the start surface
    if (surface == navigator.startSurface(state.navigation)) {
      updateStage = MaterialUpdateStage::PostUpdate;
      // Or is it the target surface ?
    } else if (surface == navigator.targetSurface(state.navigation)) {
      updateStage = MaterialUpdateStage::PreUpdate;
    }

    // Retrieve the material properties
    slab = navigator.currentSurface(state.navigation)
               ->surfaceMaterial()
               ->materialSlab(pos, navDir, updateStage);

    // Correct the material properties for non-zero incidence
    pathCorrection = surface->pathCorrection(state.geoContext, pos, dir);
    slab.scaleThickness(pathCorrection);

    // Get the surface material & properties from them
    return slab;
  }

  void evaluatePointwiseMaterialInteraction(bool multipleScattering,
                                            bool energyLoss);

  template <typename propagator_state_t, typename stepper_t>
  void updateState(propagator_state_t& state, const stepper_t& stepper,
                   NoiseUpdateMode updateMode = addNoise) {
    // in forward(backward) propagation, energy decreases(increases) and
    // variances increase(decrease)
    const auto nextE = std::hypot(mass, momentum) - Eloss * navDir;
    // put particle at rest if energy loss is too large
    nextP = (mass < nextE) ? std::sqrt(nextE * nextE - mass * mass) : 0;
    // minimum momentum below which we will not push particles via material
    // update
    // TODO 10 MeV might be quite low and we should make this configurable
    static constexpr double minP = 10 * Acts::UnitConstants::MeV;
    nextP = std::max(minP, nextP);
    // update track parameters and covariance
    stepper.update(state.stepping, pos, dir,
                   std::copysign(absQ / nextP, qOverP), time);
    state.stepping.cov(eBoundPhi, eBoundPhi) = updateVariance(
        state.stepping.cov(eBoundPhi, eBoundPhi), variancePhi, updateMode);
    state.stepping.cov(eBoundTheta, eBoundTheta) =
        updateVariance(state.stepping.cov(eBoundTheta, eBoundTheta),
                       varianceTheta, updateMode);
    state.stepping.cov(eBoundQOverP, eBoundQOverP) =
        updateVariance(state.stepping.cov(eBoundQOverP, eBoundQOverP),
                       varianceQoverP, updateMode);
  }

 private:
  void covarianceContributions(bool multipleScattering, bool energyLoss);

  double updateVariance(double variance, double change,
                        NoiseUpdateMode updateMode = addNoise) const;
};

}  // namespace detail
}  // end of namespace Acts