added SST

README.md

@@ -26,7 +26,7 @@ The SHiP geometry is described using GeoModel and is used by the simulation and
 | DecayVolume | Approximate | Rectangular vessel (should be frustum) |
 | TimingDetector | Complete | 330 scintillator bars via GeoModelXML |
 | UpstreamTagger | Approximate | Monolithic slab (needs bar segmentation) |
-| Trackers | Envelope only | 4 empty station boxes |
+| Trackers | Complete | 4 stations, 4 stereo views each, 9600 straw tubes |
 | Calorimeter | Simulation-ready | ECAL + HCAL sampling layers driven by `calo.toml` (Pb/PVT/HPL + Fe/PVT) |
 
 ## Building

src/SHiPMaterials.cpp

@@ -218,6 +218,38 @@ void SHiPMaterials::createMaterials() {
         polystyrene->lock();
         m_materials["Polystyrene"] = polystyrene;
     }
+
+    // Mylar / PET (density 1.39 g/cm³): C10H8O4 — straw tube walls
+    // MW = 10*12.011 + 8*1.008 + 4*15.999 = 192.166 g/mol
+    {
+        const double awC = 12.011;
+        const double awH = 1.008;
+        const double awO = 15.999;
+        const double mw = 10.0 * awC + 8.0 * awH + 4.0 * awO;
+        GeoMaterial* mylar =
+            new GeoMaterial("Mylar", 1.39 * GeoModelKernelUnits::g / GeoModelKernelUnits::cm3);
+        mylar->add(m_elements["Carbon"], 10.0 * awC / mw);
+        mylar->add(m_elements["Hydrogen"], 8.0 * awH / mw);
+        mylar->add(m_elements["Oxygen"], 4.0 * awO / mw);
+        mylar->lock();
+        m_materials["Mylar"] = mylar;
+    }
+
+    // ArCO2_70_30 (density 1.56e-3 g/cm³): 70% Ar + 30% CO2 by mass —
+    // straw tube gas fill. The CO2 mass fraction is split into its C and O
+    // constituents (C: 12.011/44.009, O: 2*15.999/44.009 of the CO2 mass).
+    {
+        const double mwCO2 = 44.009;
+        const double fracAr = 0.70;
+        const double fracCO2 = 0.30;
+        GeoMaterial* arco2 = new GeoMaterial(
+            "ArCO2_70_30", 1.56e-3 * GeoModelKernelUnits::g / GeoModelKernelUnits::cm3);
+        arco2->add(m_elements["Argon"], fracAr);
+        arco2->add(m_elements["Carbon"], fracCO2 * 12.011 / mwCO2);
+        arco2->add(m_elements["Oxygen"], fracCO2 * 2.0 * 15.999 / mwCO2);
+        arco2->lock();
+        m_materials["ArCO2_70_30"] = arco2;
+    }
 }
 
 }  // namespace SHiPGeometry

subsystems/Trackers/README.md

@@ -4,40 +4,110 @@ Straw tube tracking stations.
 
 ## Description
 
-The Trackers subsystem implements 4 tracking stations for the SHiP spectrometer. Each station currently consists of an empty air box at the correct z-position. The full implementation requires straw tube modules with individual straws, stereo views, and support structures.
+The Trackers subsystem implements 4 straw tracking stations for the SHiP
+spectrometer. Each station envelope is filled with 4 stereo views; each
+view is a material frame (FairShip-style hollow rectangle) enclosing a
+staggered double sub-layer of straw tubes.
 
-## Geometry Tree
+A straw is a Mylar-walled cylinder filled with an Ar/CO₂ gas mixture. The
+four views per station are rotated about the beam axis by alternating
+stereo angles so that crossing straws give a space point.
+
+The spectrometer dipole between stations 2 and 3 is a separate subsystem
+(see `subsystems/Magnet`) and is not described here.
+
+## Geometry tree
 
 ```
-TrackersContainer (Air, 6000×6860×6000 mm)
- ├─ TrackerStation_1 (Air, 6000×6860×1000 mm)  z = 84070 mm
- ├─ TrackerStation_2 (Air)                       z = 86070 mm
- ├─ TrackerStation_3 (Air)                       z = 93070 mm
- └─ TrackerStation_4 (Air)                       z = 95070 mm
+/SHiP/trackers (Air, 3000 × 3430 × 6000 mm half-extents)
+ ├─ /SHiP/trackers/station_<n> (Air, 3000 × 3430 × 500 mm)   n = 1..4
+ │    └─ /SHiP/trackers/station_<n>/view_<v>/envelope (Air)   v = 0..3
+ │       (rotated about Z by the view stereo angle)
+ │         ├─ .../frame_body      (Aluminium, hollow rectangle = outer − aperture)
+ │         ├─ .../sublayer_0_body (Air slab, 300 straws)
+ │         └─ .../sublayer_1_body (Air slab, 300 straws, half-pitch staggered)
+ │               └─ .../straw_<i>
+ │                    └─ straw_wall_<uid> (Mylar tube)
+ │                         └─ straw_gas_<uid> (ArCO2_70_30 tube)
+ └─ /SHiP/trackers/tracker_magnet (Air, inert marker box)
 ```
 
+Station Z positions (centres): 84070, 86070, 93070, 95070 mm.
 Position in world: centred at z = 89570 mm (average of stations 1 and 4).
 Stations 1-2 are upstream of the magnet, stations 3-4 downstream.
 
+## Tracker magnet
+
+`/SHiP/trackers/tracker_magnet` is an inert, air-filled marker volume for
+the tracker magnet, centred at z = 86820 mm with a 460 mm Z extent.
+
+It is **not** a physically-scaled dipole. The spectrometer dipole proper is
+the separate `Magnet` subsystem (iron yoke + coils) occupying z = 87.07 to
+92.07 m. The only space inside the trackers container that is clear of both
+the straw stations and that yoke is the ~0.5 m gap between station 2 and the
+yoke, so the marker is sized and placed to fit there without overlap.
+
+The marker exists so the tracker magnet has a named placeholder in the
+geometry; simulation/field code can locate it by its log-volume name. A
+physically-scaled magnet, if required, belongs in the `Magnet` subsystem.
+
+## Parameters
+
+| Parameter | Value |
+| --- | --- |
+| Stations | 4 |
+| Stereo views per station | 4 |
+| Sub-layers per view | 2 (half-pitch staggered) |
+| Straws per sub-layer | 300 |
+| Straws total | 4 × 4 × 2 × 300 = 9600 |
+| Straw outer diameter | 20 mm |
+| Straw length | 4000 mm (along X) |
+| Straw wall | 30 µm Mylar |
+| Straw fill | Ar/CO₂ 70/30 by mass |
+| View aperture | 4000 × 6000 mm (X × Y) |
+| View stereo angles | +2.3°, −2.3°, +2.3°, −2.3° about Z |
+| Frame bar width | 100 mm (X and Y) |
+| Frame material | Aluminium |
+
 ## Materials
 
-| Material | Density     | Usage                |
-|----------|-------------|----------------------|
-| Air      | 1.29 mg/cm³ | Container & stations |
+| Material | Density | Composition | Notes |
+| --- | --- | --- | --- |
+| Air | 1.29 mg/cm³ | already in catalog | container, station, view, sub-layer envelopes |
+| Aluminium | 2.70 g/cm³ | already in catalog | view frames |
+| Mylar | 1.39 g/cm³ | C₁₀H₈O₄, mass-fraction-normalised | straw walls |
+| ArCO2_70_30 | 1.56 mg/cm³ | 70/30 Ar/CO₂ by mass | straw gas fill |
+
+Mylar and ArCO2_70_30 are added by this subsystem to the central
+`SHiPMaterials` catalog; Air and Aluminium were already present. All
+elements required (C, H, O, Ar) were already in the element catalog.
+
+## Tests
+
+`test_trackers.cpp` exercises:
+
+- `TrackersWithinEnvelope` — station 1 exists and its box stays within the
+  CSV envelope limits (≤ 3000 × 3500 × 500 mm half-extents).
+- `TrackersHasFourStations` — all 4 station volumes are present.
+- `TrackersStationHasViews` — each station holds 4 stereo views.
+- `TrackersViewHasFrameAndSubLayers` — a view holds a frame plus two
+  sub-layers, and each sub-layer carries the full straw count.
+- `TrackersHasTrackerMagnet` — the inert `tracker_magnet` marker exists and
+  fits in the gap before the spectrometer-magnet yoke (no overlap).
 
 ## Status
 
-- [x] C++ implementation (envelope only)
-- [ ] Implement straw tube geometry
-- [ ] Add stereo views and support structures
-- [ ] Verification against GDML
+- [x] C++ implementation (straw-level geometry)
+- [x] 4 stations × 4 stereo views
+- [x] Straw tubes (Mylar wall + Ar/CO₂ gas)
+- [x] Staggered double sub-layers
+- [x] FairShip-style view frames
+- [x] Inert TrackerMagnet marker volume
+- [x] Mylar and ArCO2_70_30 materials
+- [ ] Verification against a reference GDML
 
 ## TODO
 
-- Implement straw tube modules within each station (major work)
-  - Individual straw tubes (mylar + gas)
-  - 4 views per station (Y, U, V, Y') with stereo angles
-  - Support frames and service volumes
-- Add straw tube gas material (Ar/CO2 mixture) to SHiPMaterials
-- Add mylar material to SHiPMaterials
-- Verify station positions against GDML reference
+- Verify straw pitch, view spacing and station positions against the GDML
+  reference once the tracker design is fixed.
+- Add support frames and service volumes beyond the per-view frame.

subsystems/Trackers/include/Trackers/TrackersFactory.h

@@ -3,50 +3,151 @@
 
 #pragma once
 
+#include <array>
+#include <string>
+
 class GeoPhysVol;
 
 namespace SHiPGeometry {
 
 class SHiPMaterials;
 
 /**
- * @brief Factory for the Trackers (straw tube tracking stations) geometry
+ * @brief Factory for the Trackers (straw tube tracking stations) geometry.
  *
- * Creates 4 tracking stations from GDML reference (statbox solid):
+ * Builds 4 straw tracking stations for the SHiP spectrometer. Station
+ * envelopes and z-positions follow the GDML reference / subsystem_envelopes.csv:
  * - Station 1: Z 83.57-84.57 m → centre 84.07 m
  * - Station 2: Z 85.57-86.57 m → centre 86.07 m
  * - Station 3: Z 92.57-93.57 m → centre 93.07 m
  * - Station 4: Z 94.57-95.57 m → centre 95.07 m
- * GDML statbox: x=600 cm, y=686 cm, z=100 cm → half: 300×343×50 cm
+ * Station envelope (GDML statbox): half 3000 × 3430 × 500 mm.
+ *
+ * Each station envelope is filled with 4 stereo views. A view is a material
+ * frame (FairShip-style hollow rectangle) enclosing a staggered double
+ * sub-layer of straw tubes:
+ * - Straw: 20 mm outer diameter, 4 m long, horizontal (along X).
+ * - Wall:  30 µm Mylar; fill: Ar/CO₂ 70/30 by mass.
+ * - View stereo angles about the beam axis Z: +2.3°, -2.3°, +2.3°, -2.3°.
+ *
+ * The spectrometer dipole between stations 2 and 3 is a separate subsystem
+ * (see subsystems/Magnet) and is intentionally not described here.
  */
 class TrackersFactory {
    public:
     explicit TrackersFactory(SHiPMaterials& materials);
     ~TrackersFactory() = default;
 
     /**
-     * @brief Build the Trackers geometry
-     * @return Pointer to container volume with all 4 stations
+     * @brief Build the Trackers geometry.
+     * @return Pointer to the container volume holding all 4 stations.
      */
     GeoPhysVol* build();
 
+    // ── Straw / view geometry constants (mm) ────────────────────────────
+    static constexpr int s_nStations = 4;
+    static constexpr int s_nViews = 4;      ///< stereo views per station
+    static constexpr int s_nSubLayers = 2;  ///< staggered straw layers per view
+
+    static constexpr double s_strawRadius = 10.0;     ///< 1 cm radius (2 cm diam)
+    static constexpr double s_strawLength = 4000.0;   ///< 4 m, along X
+    static constexpr double s_wallThickness = 0.030;  ///< 30 µm Mylar wall
+
+    /// Active aperture inside a view frame (X = straw length region, Y = pitch).
+    static constexpr double s_apertureX = 4000.0;
+    static constexpr double s_apertureY = 6000.0;
+
+    /// Straws per sub-layer (aperture height / straw diameter).
+    static constexpr int s_nStraws = static_cast<int>(s_apertureY / (2.0 * s_strawRadius));
+
+    static constexpr double s_stereoAngleDeg = 2.3;  ///< |stereo angle| per view
+
+    // View frame (FairShip-style hollow rectangle).
+    static constexpr double s_frameBarX = 100.0;  ///< frame bar width in X
+    static constexpr double s_frameBarY = 100.0;  ///< frame bar width in Y
+    static constexpr double s_frameHalfZ = 22.0;  ///< frame half-thickness in Z
+
+    // ── 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;    ///< centre, mm
+    static constexpr double s_trackerMagnetHalfZ = 230.0;  ///< half-depth, mm
+
    private:
     SHiPMaterials& m_materials;
 
-    // Station dimensions from GDML statbox (mm)
+    /// Frame material name in the central SHiPMaterials catalogue.
+    std::string m_frameMaterialName = "Aluminium";
+
+    // ── Station envelope from GDML statbox (mm) ─────────────────────────
     static constexpr double s_halfX = 3000.0;  // 300 cm
-    static constexpr double s_halfY = 3430.0;  // 343 cm (GDML y=686 cm)
+    static constexpr double s_halfY = 3430.0;  // 343 cm (GDML y = 686 cm)
     static constexpr double s_halfZ = 500.0;   // 50 cm
 
-    // Station Z positions (centres, in mm from origin)
+    // Station Z positions (centres, mm from origin).
     static constexpr double s_station1Z = 84070.0;  // 84.07 m
     static constexpr double s_station2Z = 86070.0;  // 86.07 m
     static constexpr double s_station3Z = 93070.0;  // 93.07 m
     static constexpr double s_station4Z = 95070.0;  // 95.07 m
 
-    // Container dimensions (spans all stations)
+    // 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 ───────────────────────────────────────────────
+
+    /**
+     * @brief Build one station envelope and place its 4 stereo views.
+     * @param stationIndex 0-based station index (0..3).
+     * @return The station envelope physical volume.
+     */
+    GeoPhysVol* buildStation(int stationIndex);
+
+    /**
+     * @brief Build one stereo view: a frame plus two staggered sub-layers.
+     * @param stationIndex 0-based parent station index, used for unique names.
+     * @param viewIndex    0-based view index within the station (0..3).
+     * @return The (unrotated) view physical volume.
+     */
+    GeoPhysVol* buildView(int stationIndex, int viewIndex);
+
+    /**
+     * @brief Build the FairShip-style hollow-rectangle frame for one view.
+     * @param stationIndex 0-based parent station index, used for unique names.
+     * @param viewIndex    0-based view index within the station.
+     */
+    GeoPhysVol* buildFrame(int stationIndex, int viewIndex);
+
+    /**
+     * @brief Build one sub-layer of s_nStraws parallel straws.
+     * @param stationIndex 0-based parent station index, used for unique names.
+     * @param viewIndex    0-based parent view index.
+     * @param shifted      true for the half-pitch-staggered sub-layer.
+     */
+    GeoPhysVol* buildSubLayer(int stationIndex, int viewIndex, bool shifted);
+
+    /**
+     * @brief Build a single straw: a Mylar wall cylinder with a gas core.
+     * @param uid Globally unique straw identifier, used for unique names.
+     */
+    GeoPhysVol* buildStraw(int uid);
+
+    /**
+     * @brief Build the inert TrackerMagnet marker volume (air-filled box).
+     *
+     * Placed in the gap between station 2 and the spectrometer-magnet yoke.
+     * See the note on s_trackerMagnetZ for why this is a marker rather than
+     * a physically-scaled dipole.
+     */
+    GeoPhysVol* buildTrackerMagnet();
 };
 
 }  // namespace SHiPGeometry