ActsFatras/EventData/Hit.hpp

0001 // This file is part of the Acts project.
0002 //
0003 // Copyright (C) 2020 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 http://mozilla.org/MPL/2.0/.
0008
0009 #pragma once
0010
0011 #include "Acts/Definitions/Algebra.hpp"
0012 #include "Acts/Definitions/Common.hpp"
0013 #include "Acts/Geometry/GeometryIdentifier.hpp"
0014 #include "ActsFatras/EventData/Barcode.hpp"
0015
0016 #include <cstdint>
0017
0018 namespace ActsFatras {
0019
0020 /// A simulation hit on a surface.
0021 ///
0022 /// This is the undigitized, truth hit, i.e. just a recording of the particle
0023 /// state at the surface intersection. Since Fatras is surface-based, the hit
0024 /// position is always constrained to a surface. Depending on the simulated
0025 /// interactions the momentum state before and after might differ and is
0026 /// thus stored as two separate four-vectors.
0027 class Hit {
0028  public:
0029   using Scalar = Acts::ActsScalar;
0030   using Vector3 = Acts::ActsVector<3>;
0031   using Vector4 = Acts::ActsVector<4>;
0032
0033   /// Construct default hit with (mostly) invalid information.
0034   Hit() = default;
0035   /// Construct from four-position and four-momenta.
0036   ///
0037   /// @param geometryId      Geometry identifier of the surface
0038   /// @param particleId Particle identifier of the particle that created the hit
0039   /// @param pos4       Particle space-time four-vector on the surface
0040   /// @param before4    Particle four-momentum before the interaction
0041   /// @param after4     Particle four-momentum after the interaction
0042   /// @param index_     Hit index along the particle trajectory
0043   ///
0044   /// All quantities are given in the global coordinate system. It is the
0045   /// users responsibility to ensure that the position correspond to a
0046   /// position on the given surface.
0047   Hit(Acts::GeometryIdentifier geometryId, Barcode particleId,
0048       const Vector4& pos4, const Vector4& before4, const Vector4& after4,
0049       int32_t index_ = -1)
0050       : m_geometryId(geometryId),
0051         m_particleId(particleId),
0052         m_index(index_),
0053         m_pos4(pos4),
0054         m_before4(before4),
0055         m_after4(after4) {}
0056   Hit(const Hit&) = default;
0057   Hit(Hit&&) = default;
0058   Hit& operator=(const Hit&) = default;
0059   Hit& operator=(Hit&&) = default;
0060
0061   /// Geometry identifier of the hit surface.
0062   constexpr Acts::GeometryIdentifier geometryId() const { return m_geometryId; }
0063   /// Particle identifier of the particle that generated the hit.
0064   constexpr Barcode particleId() const { return m_particleId; }
0065   /// Hit index along the particle trajectory.
0066   ///
0067   /// @retval negative if the hit index is undefined.
0068   constexpr int32_t index() const { return m_index; }
0069
0070   /// Space-time position four-vector.
0071   const Vector4& fourPosition() const { return m_pos4; }
0072   /// Three-position, i.e. spatial coordinates without the time.
0073   auto position() const { return m_pos4.segment<3>(Acts::ePos0); }
0074   /// Time coordinate.
0075   Scalar time() const { return m_pos4[Acts::eTime]; }
0076
0077   /// Particle four-momentum before the hit.
0078   const Vector4& momentum4Before() const { return m_before4; }
0079   /// Particle four-momentum after the hit.
0080   const Vector4& momentum4After() const { return m_after4; }
0081   /// Normalized particle direction vector before the hit.
0082   Vector3 directionBefore() const {
0083     return m_before4.segment<3>(Acts::eMom0).normalized();
0084   }
0085   /// Normalized particle direction vector the hit.
0086   Vector3 directionAfter() const {
0087     return m_after4.segment<3>(Acts::eMom0).normalized();
0088   }
0089   /// Average normalized particle direction vector through the surface.
0090   Vector3 direction() const {
0091     auto dir0 = m_before4.segment<3>(Acts::eMom0).normalized();
0092     auto dir1 = m_after4.segment<3>(Acts::eMom0).normalized();
0093     return ((dir0 + dir1) / 2.).segment<3>(Acts::eMom0).normalized();
0094   }
0095   /// Energy deposited by the hit.
0096   ///
0097   /// @retval positive if the particle lost energy when it passed the surface
0098   /// @retval negative if magic was involved
0099   Scalar depositedEnergy() const {
0100     return m_before4[Acts::eEnergy] - m_after4[Acts::eEnergy];
0101   }
0102
0103  private:
0104   /// Identifier of the surface.
0105   Acts::GeometryIdentifier m_geometryId;
0106   /// Identifier of the generating particle.
0107   Barcode m_particleId;
0108   /// Index of the hit along the particle trajectory.
0109   int32_t m_index = -1;
0110   /// Global space-time position four-vector.
0111   Vector4 m_pos4 = Vector4::Zero();
0112   /// Global particle energy-momentum four-vector before the hit.
0113   Vector4 m_before4 = Vector4::Zero();
0114   /// Global particle energy-momentum four-vector after the hit.
0115   Vector4 m_after4 = Vector4::Zero();
0116 };
0117
0118 }  // namespace ActsFatras