TRK: IRIS service aluminium from the MaterialManager

The IRIS service modules (addIRISServiceModules and
addIRISServiceModulesSegmented) created their medium by hand as
new TGeoMedium("ALUMINUM", 4, ...): a hard-coded medium ID 4 and all
tracking parameters 0, i.e. ifield = 0. ID 4 is already TRK_AIR$, the
medium of the TRKLayer* mother volumes and the VD petal cases.

Geant4 VMC keys media by ID (TG4GeometryManager::FillMediumMapFromRoot):
the second medium with ID 4 reuses the first one's entry and overwrites
its ifield with 0. With /mcDet/setIsZeroMagField true, every volume of
TRK_AIR$ then gets a zero field, so tracks cross each ML/OT layer
volume (1.2-1.5 cm of air around the staves) without bending. The
geometry file still shows TRK_AIR$ with ifield = 2.

A muon gun (p 2-5 GeV, |eta| < 0.8, A3IP + TRK, ALICE 3 field 2 T)
measures the field each pair of consecutive layers turned the momentum
in: before 0.84 T (7 -> 9 cm) rising to 1.95 T (60 -> 80 cm), the VD
2.00 T; after, every pair 1.99-2.01 T.

The aluminium is now registered in TRKServices::createMaterials with
the TRK's field parameters (ALICE3_TRKSERVICES_ALUMINIUM) and taken
from MaterialManager::getTGeoMedium, which gives it a unique ID. The
material is unchanged (A, Z, density, radiation and interaction
lengths).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Signed-off-by: Felix Schlepper <felix.schlepper@cern.ch>

Author: f3sch

Detectors/Upgrades/ALICE3/TRKFT3/TRK/simulation/src/TRKServices.cxx

@@ -113,6 +113,7 @@ void TRKServices::createMaterials()
   matmgr.Mixture("ALICE3_TRKSERVICES", 74, "ALUMINIUM5083", aAl5083, zAl5083, dAl5083, 9, wAl5083);                                    // AL5083 - Candidate for IRIS vacuum vessel
   matmgr.Mixture("ALICE3_TRKSERVICES", 75, "ALUMINIUMBERYLLIUMMETAL", aAlBeMet, zAlBeMet, dAlBeMet, 2, wAlBeMet);                      // Aluminium-Beryllium metal - Candidate for IRIS vacuum vessel
   matmgr.Material("ALICE3_TRKSERVICES", 76, "CARBONFIBERM55J6K", 12.0107, 6, 1.92, 22.4, 45.4);                                        // Carbon Fiber M55J
+  matmgr.Material("ALICE3_TRKSERVICES", 78, "ALUMINIUM", 26.9815, 13, 2.70, 8.897, 39.70);                                             // Aluminium for the IRIS service modules
   matmgr.Mixture("ALICE3_PIPE", 77, "VACUUM", aAir, zAir, dAir1, 4, wAir);
 
   matmgr.Medium("ALICE3_TRKSERVICES", 1, "CERAMIC", 66, 0, ifield, fieldm, tmaxfd, stemax, deemax, epsil, stmin);                  // Ceramic for cold plate
@@ -127,6 +128,7 @@ void TRKServices::createMaterials()
   matmgr.Medium("ALICE3_TRKSERVICES", 10, "ALUMINIUMBERYLLIUMMETAL", 75, 0, ifield, fieldm, tmaxfd, stemax, deemax, epsil, stmin); // AlBeMet for IRIS vacuum vessel
   matmgr.Medium("ALICE3_TRKSERVICES", 11, "CARBONFIBERM55J6K", 76, 0, ifield, fieldm, tmaxfd, stemax, deemax, epsil, stmin);       // Carbon Fiber M55J
   matmgr.Medium("ALICE3_PIPE", 12, "VACUUM", 77, 0, ifield, fieldm, tmaxfd, stemax, deemax, epsil, stmin);                         // Vacuum inside the beam pipe
+  matmgr.Medium("ALICE3_TRKSERVICES", 13, "ALUMINIUM", 78, 0, ifield, fieldm, tmaxfd, stemax, deemax, epsil, stmin);               // Aluminium for the IRIS service modules
 }
 
 void TRKServices::createServices(TGeoVolume* motherVolume)

Detectors/Upgrades/ALICE3/TRKFT3/TRK/simulation/src/VDGeometryBuilder.cxx

@@ -541,11 +541,11 @@ static void addIRISServiceModules(TGeoVolume* petalAsm, int nPetals)
     return;
   }
 
-  auto* matAl = new TGeoMaterial("ALUMINUM", 26.9815, 13, 2.70);
-  const TGeoMedium* med = new TGeoMedium("ALUMINUM", 4, matAl);
+  auto& matmgr = o2::base::MaterialManager::Instance();
+  const TGeoMedium* med = matmgr.getTGeoMedium("ALICE3_TRKSERVICES_ALUMINIUM");
 
   if (!med) {
-    LOGP(error, "addIRISServiceModules: ALUMINUM medium not found.");
+    LOGP(error, "addIRISServiceModules: ALICE3_TRKSERVICES_ALUMINIUM medium not found.");
     return;
   }
 
@@ -617,11 +617,11 @@ static void addIRISServiceModulesSegmented(TGeoVolume* petalAsm, int nPetals)
   // --- Petal φ-span (segment)
   const double halfPhi = 0.5 * (360.0 / double(nPetals));
 
-  auto* matAl = new TGeoMaterial("ALUMINUM", 26.9815, 13, 2.70);
-  const TGeoMedium* med = new TGeoMedium("ALUMINUM", 4, matAl);
+  auto& matmgr = o2::base::MaterialManager::Instance();
+  const TGeoMedium* med = matmgr.getTGeoMedium("ALICE3_TRKSERVICES_ALUMINIUM");
 
   if (!med) {
-    LOGP(error, "addIRISServiceModules: ALUMINUM medium not found.");
+    LOGP(error, "addIRISServiceModulesSegmented: ALICE3_TRKSERVICES_ALUMINIUM medium not found.");
     return;
   }