ParticleTests.cpp

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// 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/.

#include <boost/test/unit_test.hpp>

#include "Acts/Tests/CommonHelpers/FloatComparisons.hpp"
#include "Acts/Utilities/Units.hpp"
#include "ActsFatras/EventData/Particle.hpp"

#include <limits>

using Acts::PdgParticle;
using ActsFatras::Barcode;
using ActsFatras::Particle;
using namespace Acts::UnitLiterals;

namespace {
constexpr auto eps = std::numeric_limits<Particle::Scalar>::epsilon();
}

BOOST_AUTO_TEST_SUITE(FatrasParticle)

BOOST_AUTO_TEST_CASE(Construct) {
  const auto pid = Barcode().setVertexPrimary(1).setParticle(42);
  const auto particle = Particle(pid, PdgParticle::eProton, 1_GeV, 1_e);

  BOOST_CHECK_EQUAL(particle.particleId(), pid);
  BOOST_CHECK_EQUAL(particle.pdg(), PdgParticle::eProton);
  // particle is at rest at the origin
  BOOST_CHECK_EQUAL(particle.position4(), Particle::Vector4::Zero());
  BOOST_CHECK_EQUAL(particle.position(), Particle::Vector3::Zero());
  BOOST_CHECK_EQUAL(particle.time(), Particle::Scalar(0));
  BOOST_CHECK_EQUAL(particle.position4().x(), particle.position().x());
  BOOST_CHECK_EQUAL(particle.position4().y(), particle.position().y());
  BOOST_CHECK_EQUAL(particle.position4().z(), particle.position().z());
  BOOST_CHECK_EQUAL(particle.position4().w(), particle.time());
  // particle direction is undefined, but must be normalized
  CHECK_CLOSE_REL(particle.unitDirection().norm(), 1, eps);
  BOOST_CHECK_EQUAL(particle.transverseMomentum(), Particle::Scalar(0));
  BOOST_CHECK_EQUAL(particle.absMomentum(), Particle::Scalar(0));
  // particle is created at rest and thus not alive
  BOOST_CHECK(not particle);
}

BOOST_AUTO_TEST_CASE(CorrectEnergy) {
  const auto pid = Barcode().setVertexPrimary(1).setParticle(42);
  auto particle = Particle(pid, PdgParticle::eProton, 1_GeV, 1_e)
                      .setDirection(Particle::Vector3::UnitX())
                      .setAbsMomentum(2_GeV);

  BOOST_CHECK_EQUAL(particle.mass(), 1_GeV);
  // check that the particle has some input energy
  BOOST_CHECK_EQUAL(particle.momentum4().x(), 2_GeV);
  BOOST_CHECK_EQUAL(particle.momentum4().y(), 0_GeV);
  BOOST_CHECK_EQUAL(particle.momentum4().z(), 0_GeV);
  BOOST_CHECK_EQUAL(particle.momentum4().w(), std::hypot(1_GeV, 2_GeV));
  BOOST_CHECK_EQUAL(particle.transverseMomentum(), 2_GeV);
  BOOST_CHECK_EQUAL(particle.absMomentum(), 2_GeV);
  BOOST_CHECK_EQUAL(particle.energy(), std::hypot(1_GeV, 2_GeV));
  // particle direction must be normalized
  CHECK_CLOSE_REL(particle.unitDirection().norm(), 1, eps);
  // loose some energy
  particle.correctEnergy(-100_MeV);
  BOOST_CHECK_LT(particle.transverseMomentum(), 2_GeV);
  BOOST_CHECK_LT(particle.absMomentum(), 2_GeV);
  BOOST_CHECK_EQUAL(particle.energy(),
                    Particle::Scalar(std::hypot(1_GeV, 2_GeV) - 100_MeV));
  CHECK_CLOSE_REL(particle.unitDirection().norm(), 1, eps);
  // particle is still alive
  BOOST_CHECK(particle);
  // loose a lot of energy
  particle.correctEnergy(-3_GeV);
  BOOST_CHECK_EQUAL(particle.transverseMomentum(), Particle::Scalar(0));
  BOOST_CHECK_EQUAL(particle.absMomentum(), Particle::Scalar(0));
  BOOST_CHECK_EQUAL(particle.energy(), particle.mass());
  CHECK_CLOSE_REL(particle.unitDirection().norm(), 1, eps);
  // lossing even more energy does nothing
  particle.correctEnergy(-10_GeV);
  BOOST_CHECK_EQUAL(particle.transverseMomentum(), Particle::Scalar(0));
  BOOST_CHECK_EQUAL(particle.absMomentum(), Particle::Scalar(0));
  BOOST_CHECK_EQUAL(particle.energy(), particle.mass());
  CHECK_CLOSE_REL(particle.unitDirection().norm(), 1, eps);
  // particle is not alive anymore
  BOOST_CHECK(not particle);
}

BOOST_AUTO_TEST_SUITE_END()