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 // This file is part of the ACTS project.
 //
 // Copyright (C) 2016 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 https://mozilla.org/MPL/2.0/.
 
 #include "Acts/Definitions/ParticleData.hpp"
 
 #include "Acts/Definitions/PdgParticle.hpp"
 
 #include <algorithm>
 #include <array>
 #include <cassert>
 #include <cmath>
 #include <cstdint>
 #include <iterator>
 #include <limits>
 #include <optional>
 #include <ostream>
 #include <type_traits>
 #include <utility>
 
 #include "ParticleDataTable.hpp"
 
 namespace {
 
 enum class Type {
   Charge,
   Mass,
   Name,
 };
 
 // Template function depending on the PDG and *type* of data
 // so we can use statically cached values
 template <typename T, Acts::PdgParticle pdg, Type type>
 std::optional<T> findCachedImpl(const std::map<std::int32_t, T>& map) {
   const static std::optional<T> value = [&map]() -> std::optional<T> {
     const auto it = map.find(static_cast<std::int32_t>(pdg));
     if (it == map.end()) {
       return std::nullopt;
     }
     return it->second;
   }();
 
   return value;
 }
 
 // Cache lookup for particle data
 // Uses a switch statement to map the PDG code to the correct cached value
 template <typename T, Type type>
 std::optional<T> findCached(Acts::PdgParticle pdg,
                             const std::map<std::int32_t, T>& map) {
   using enum Acts::PdgParticle;
   switch (pdg) {
     case eElectron:
       return findCachedImpl<T, eElectron, type>(map);
     case ePositron:
       return findCachedImpl<T, ePositron, type>(map);
     case eMuon:
       return findCachedImpl<T, eMuon, type>(map);
     case eAntiMuon:
       return findCachedImpl<T, eAntiMuon, type>(map);
     case eTau:
       return findCachedImpl<T, eTau, type>(map);
     case eAntiTau:
       return findCachedImpl<T, eAntiTau, type>(map);
     case eGamma:
       return findCachedImpl<T, eGamma, type>(map);
     case ePionZero:
       return findCachedImpl<T, ePionZero, type>(map);
     case ePionPlus:
       return findCachedImpl<T, ePionPlus, type>(map);
     case ePionMinus:
       return findCachedImpl<T, ePionMinus, type>(map);
     case eKaonPlus:
       return findCachedImpl<T, eKaonPlus, type>(map);
     case eKaonMinus:
       return findCachedImpl<T, eKaonMinus, type>(map);
     case eNeutron:
       return findCachedImpl<T, eNeutron, type>(map);
     case eAntiNeutron:
       return findCachedImpl<T, eAntiNeutron, type>(map);
     case eProton:
       return findCachedImpl<T, eProton, type>(map);
     case eAntiProton:
       return findCachedImpl<T, eAntiProton, type>(map);
     case eLead:
       return findCachedImpl<T, eLead, type>(map);
     default:
       return std::nullopt;
   }
 }
 
 }  // namespace
 
 std::optional<float> Acts::findCharge(Acts::PdgParticle pdg) {
   if (auto cached = findCached<float, Type::Charge>(pdg, kParticlesMapCharge);
       cached) {
     return cached;
   }
 
   const auto it = kParticlesMapCharge.find(pdg);
   if (it == kParticlesMapCharge.end()) {
     if (isNucleus(pdg)) {
       return Acts::findChargeOfNucleus(pdg);
     } else {
       return std::nullopt;
     }
   }
   return it->second;
 }
 
 float Acts::findChargeOfNucleus(Acts::PdgParticle pdg) {
   if (!isNucleus(pdg)) {
     throw std::invalid_argument("PDG must represent a nucleus");
   }
   auto pdgGround = makeNucleusGroundState(pdg);
   const auto it = kParticlesMapCharge.find(pdgGround);
   if (it == kParticlesMapCharge.end()) {
     // extract charge from PDG number
     auto ZandA = extractNucleusZandA(pdg);
     return static_cast<float>(ZandA.first);
   }
   return it->second;
 }
 
 std::optional<float> Acts::findMass(Acts::PdgParticle pdg) {
   if (auto cached = findCached<float, Type::Mass>(pdg, kParticlesMapMass);
       cached) {
     return cached;
   }
 
   const auto it = kParticlesMapMass.find(pdg);
   if (it == kParticlesMapMass.end()) {
     if (isNucleus(pdg)) {
       return Acts::findMassOfNucleus(pdg);
     } else {
       return std::nullopt;
     }
   }
   return it->second;
 }
 
 float Acts::findMassOfNucleus(Acts::PdgParticle pdg) {
   if (!isNucleus(pdg)) {
     throw std::invalid_argument("PDG must represent a nucleus");
   }
   auto pdgGround = makeNucleusGroundState(pdg);
   const auto it = kParticlesMapMass.find(pdgGround);
   if (it == kParticlesMapMass.end()) {
     // calculate mass using Bethe-Weizsacker formula
     return calculateNucleusMass(pdg);
   }
   return it->second;
 }
 
 float Acts::calculateNucleusMass(Acts::PdgParticle pdg) {
   if (!isNucleus(pdg)) {
     throw std::invalid_argument("PDG must represent a nucleus");
   }
 
   auto ZandA = extractNucleusZandA(pdg);
   int Z = std::abs(ZandA.first);
   int A = ZandA.second;
 
   float a_Vol = 15.260f * Acts::UnitConstants::MeV;
   float a_Surf = 16.267f * Acts::UnitConstants::MeV;
   float a_Col = 0.689f * Acts::UnitConstants::MeV;
   float a_Sym = 22.209f * Acts::UnitConstants::MeV;
   float a_Pair =
       (1 - 2 * (Z % 2)) * (1 - A % 2) * 10.076f * Acts::UnitConstants::MeV;
 
   float massP = 0.938272f * Acts::UnitConstants::GeV;
   float massN = 0.939565f * Acts::UnitConstants::GeV;
 
   float bindEnergy = 0.f;
   bindEnergy += a_Vol * A;
   bindEnergy -= a_Surf * std::pow(A, 2. / 3.);
   bindEnergy -= a_Col * Z * (Z - 1) * std::pow(A, -1. / 3.);
   bindEnergy -= a_Sym * std::pow(A - 2 * Z, 2.) / A;
   bindEnergy -= a_Pair * std::pow(A, -1. / 2.);
 
   return massP * Z + massN * (A - Z) - bindEnergy;
 }
 
 std::optional<std::string_view> Acts::findName(Acts::PdgParticle pdg) {
   if (auto cached =
           findCached<const char* const, Type::Name>(pdg, kParticlesMapName);
       cached) {
     return cached;
   }
 
   const auto it = kParticlesMapName.find(pdg);
   if (it == kParticlesMapName.end()) {
     if (isNucleus(pdg)) {
       return Acts::findNameOfNucleus(pdg);
     } else {
       return std::nullopt;
     }
   }
   return it->second;
 }
 
 std::optional<std::string_view> Acts::findNameOfNucleus(Acts::PdgParticle pdg) {
   if (!isNucleus(pdg)) {
     throw std::invalid_argument("PDG must represent a nucleus");
   }
 
   auto pdgGround = makeNucleusGroundState(pdg);
   const auto it = kParticlesMapName.find(pdgGround);
   if (it == kParticlesMapName.end()) {
     return std::nullopt;
   }
   return it->second;
 }
 
 std::optional<Acts::ParticleData> Acts::findParticleData(PdgParticle pdg) {
   auto charge = findCharge(pdg);
   auto mass = findMass(pdg);
   auto name = findName(pdg);
 
   if (charge.has_value() && mass.has_value() && name.has_value()) {
     return ParticleData{charge.value(), mass.value(), name.value()};
   }
 
   return std::nullopt;
 }
 
 std::ostream& Acts::operator<<(std::ostream& os, Acts::PdgParticle pdg) {
   const auto name = Acts::findName(pdg);
   if (name) {
     os << *name;
   } else {
     os << static_cast<std::int32_t>(pdg);
   }
   return os;
 }
 
 std::optional<std::string_view> Acts::pdgToShortAbsString(PdgParticle pdg) {
   pdg = makeAbsolutePdgParticle(pdg);
   if (pdg == eElectron) {
     return "e";
   }
   if (pdg == eMuon) {
     return "mu";
   }
   if (pdg == eTau) {
     return "t";
   }
   if (pdg == eGamma) {
     return "g";
   }
   if (pdg == ePionZero) {
     return "pi0";
   }
   if (pdg == ePionPlus) {
     return "pi";
   }
   if (pdg == eKaonPlus) {
     return "K";
   }
   if (pdg == eNeutron) {
     return "n";
   }
   if (pdg == eProton) {
     return "p";
   }
   if (pdg == eLead) {
     return "lead";
   }
   return std::nullopt;
 }

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