TrackersFactory.h

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// SPDX-License-Identifier: LGPL-3.0-or-later
// Copyright (C) CERN for the benefit of the SHiP Collaboration
 
#pragma once
 
#include <GeoModelKernel/Units.h>
 
#include <array>
#include <string>
 
class GeoPhysVol;
 
namespace SHiPGeometry {
 
class SHiPMaterials;
 
class TrackersFactory {
   public:
    explicit TrackersFactory(SHiPMaterials& materials);
    ~TrackersFactory() = default;
 
    [[nodiscard]] GeoPhysVol* build();
 
    // ── Straw / view geometry constants ─────────────────────────────────
    // Unit shorthand (GeoModel's native length unit is mm)
    static constexpr double mm = GeoModelKernelUnits::mm;
 
    static constexpr int s_nStations = 4;
    static constexpr int s_nViews = 4;      
    static constexpr int s_nSubLayers = 2;  
 
    static constexpr double s_strawRadius = 10.0 * mm;     
    static constexpr double s_strawLength = 4000.0 * mm;   
    static constexpr double s_wallThickness = 0.030 * mm;  
 
    static constexpr double s_apertureX = 4000.0 * mm;
    static constexpr double s_apertureY = 6000.0 * mm;
 
    static constexpr int s_nStraws = static_cast<int>(s_apertureY / (2.0 * s_strawRadius));
 
    static constexpr double s_stereoAngleDeg = 2.3;  
 
    // View frame (FairShip-style hollow rectangle).
    static constexpr double s_frameBarX = 100.0 * mm;  
    static constexpr double s_frameBarY = 100.0 * mm;  
    static constexpr double s_frameHalfZ = 22.0 * mm;  
 
    // ── Tracker magnet ──────────────────────────────────────────────────
    // An inert, air-filled marker volume named "TrackerMagnet", placed in
    // the clear gap between station 2 and the spectrometer-magnet yoke.
    //
    // NOTE: this is NOT a physically-scaled dipole. The spectrometer dipole
    // proper is the separate Magnet subsystem (iron yoke + coils) occupying
    // z = 87.07-92.07 m. The only free space inside the trackers container
    // and clear of that yoke is a ~0.5 m gap, so this marker is sized to fit
    // there. It exists so the tracker magnet has a named placeholder in the
    // geometry; simulation/field code can locate it by the name
    // "/SHiP/trackers/tracker_magnet".
    static constexpr double s_trackerMagnetZ = 86820.0 * mm;    
    static constexpr double s_trackerMagnetHalfZ = 230.0 * mm;  
 
   private:
    SHiPMaterials& m_materials;
 
    std::string m_frameMaterialName = "Aluminium";
 
    // ── Station envelope from GDML statbox ──────────────────────────────
    static constexpr double s_halfX = 3000.0 * mm;  // 300 cm
    static constexpr double s_halfY = 3430.0 * mm;  // 343 cm (GDML y = 686 cm)
    static constexpr double s_halfZ = 500.0 * mm;   // 50 cm
 
    // Station Z positions (centres, from origin).
    static constexpr double s_station1Z = 84070.0 * mm;  // 84.07 m
    static constexpr double s_station2Z = 86070.0 * mm;  // 86.07 m
    static constexpr double s_station3Z = 93070.0 * mm;  // 93.07 m
    static constexpr double s_station4Z = 95070.0 * mm;  // 95.07 m
 
    // Container dimensions (spans all stations).
    static constexpr double s_containerHalfZ = (s_station4Z - s_station1Z) / 2.0 + s_halfZ;
    static constexpr double s_containerCentreZ = (s_station1Z + s_station4Z) / 2.0;
 
    // ── Internal builders ───────────────────────────────────────────────
 
    GeoPhysVol* buildStation(int stationIndex);
 
    GeoPhysVol* buildView(int stationIndex, int viewIndex);
 
    GeoPhysVol* buildFrame(int stationIndex, int viewIndex);
 
    GeoPhysVol* buildSubLayer(int stationIndex, int viewIndex, bool shifted);
 
    GeoPhysVol* buildStraw();
 
    GeoPhysVol* m_strawPhys = nullptr;
 
    GeoPhysVol* buildTrackerMagnet();
};
 
}  // namespace SHiPGeometry