Let the ZEM calorimeters be built without the far beam line

[sawenzel]

This adds two ZDCSimParam switches so a simulation can keep the ZEM geometry without paying for transport to the ZN/ZP calorimeters at +-113 m.

• The ZDC geometry is the +-113 m beam line, its magnets, ZN, ZP and ZEM; the transport cost is the beam line, while ZEM sits at z = 7.6 m.
• buildBeamLine=false skips the beam line, the magnets and ZN/ZP; buildZEM controls the ZEM calorimeters.
• The ZN and ZP construction moves into createZNZP() and the ZEM construction into createZEM(), so createDetectors() shows what depends on the beam line.
• The PMC and PMQ medium ids move ahead of that branch: ProcessHits compares every step against them for ZEM too, so leaving them in the ZN block gave ZEM hits with no energy loss and no light yield.
• The ZN/ZP sensitive volume lookups are guarded so they no longer abort when the volumes are absent.
• 20 pythia8pp events with TGeant3: 276.9 s with the full ZDC, 141.6 +- 1.1 s with --skipModules ZDC, 136.9 +- 1.9 s with buildBeamLine=false.
• 50 events of 20 muons at 200 GeV into 4.6 < eta < 5.3 give 234 ZEM hits with 2167 photoelectrons at buildBeamLine=false, against 230 hits and 2097 with the full ZDC.

https://its.cern.ch/jira/browse/O2-7158

[coppedis]

Dear @sawenzel ,
the ZEM calorimeters have been removed to leave space for the FoCal.They won't be used anymore in simulation.
Anyway the proposed change is fine with us.

Kind regards, Chiara

[sawenzel]

@coppedis : Thanks for the info. I agree, but we might still need to run Run3 simulations which needs this fix.

[alibuild]

Error while checking build/O2/fullCI_slc9 for cfa5bc2 at 2026-09-04 15:04:

## sw/BUILD/o2checkcode-latest/log
--
========== List of errors found ==========
++ GRERR=0
++ grep -v clang-diagnostic-error error-log.txt
++ grep ' error:'
++ GRERR=1
++ [[ 1 == 0 ]]
++ mkdir -p /sw/INSTALLROOT/4d3ac29be8b363b73088cdce75db60b86d4c4775/slc9_x86-64/o2checkcode/1.0-local551/etc/modulefiles
++ alibuild-generate-module
+ HAS_BIN=
+ HAS_LIB=
+ HAS_CMAKE=
+ HAS_ROOT=
+ '[' 0 '!=' 0 ']'
+ cat
+ printf 'if ![ is-loaded '\''BASE/1.0'\'' ] {\n module load BASE/1.0\n}'
+ echo 'BUILD_REQUIRES=CMake alibuild-recipe-tools defaults-release'
BUILD_REQUIRES=CMake alibuild-recipe-tools defaults-release
+ FULL_BUILD_REQUIRES='pytorch_cpuinfo Alice-GRID-Utils safe_int ninja alibuild-recipe-tools O2-customization defaults-release json-c MPFR double-conversion googlebenchmark ninja-fortran bz2 UUID CMake Python-modules-list FairCMakeModules date'
+ echo 'FULL_BUILD_REQUIRES=pytorch_cpuinfo Alice-GRID-Utils safe_int ninja alibuild-recipe-tools O2-customization defaults-release json-c MPFR double-conversion googlebenchmark ninja-fortran bz2 UUID CMake Python-modules-list FairCMakeModules date'
FULL_BUILD_REQUIRES=pytorch_cpuinfo Alice-GRID-Utils safe_int ninja alibuild-recipe-tools O2-customization defaults-release json-c MPFR double-conversion googlebenchmark ninja-fortran bz2 UUID CMake Python-modules-list FairCMakeModules date
++ cut -f1 -d=
++ env
++ grep -v '^DEFAULT_'
++ grep -v PKGREVISION
++ grep -v ALIBUILD_RECIPE_TOOLS
++ grep REVISION
++ sed -e s/_REVISION//
+ for x in $(env | cut -f1 -d= | grep -v "^DEFAULT_" | grep -v PKGREVISION | grep -v ALIBUILD_RECIPE_TOOLS | grep REVISION | sed -e 's/_REVISION//')
++ eval 'echo $LIBFFI_REVISION'
+++ echo 14
+ REVISION_VALUE=14
++ eval 'echo $LIBFFI_VERSION'
+++ echo v3.2.1-alice1
+ VERSION_VALUE=v3.2.1-alice1
++ eval 'echo $LIBFFI_ROOT'
+++ echo /sw/slc9_x86-64/libffi/v3.2.1-alice1-14
+ ROOT_PATH_VALUE=/sw/slc9_x86-64/libffi/v3.2.1-alice1-14
+ '[' -z 14 ']'
+ echo 'pytorch_cpuinfo Alice-GRID-Utils safe_int ninja alibuild-recipe-tools O2-customization defaults-release json-c MPFR double-conversion googlebenchmark ninja-fortran bz2 UUID CMake Python-modules-list FairCMakeModules date'
+ tr '[:lower:]' '[:upper:]'
+ tr - _
+ tr ' ' '\n'
+ grep -q '^LIBFFI$'
+ '[' '!' -d /sw/slc9_x86-64/libffi/v3.2.1-alice1-14/etc/modulefiles ']'
++ find /sw/slc9_x86-64/libffi/v3.2.1-alice1-14/etc/modulefiles -type f '!' -name '*.*' -print0
++ xargs -0 -n1 basename
+ for filename in $(find "$ROOT_PATH_VALUE/etc/modulefiles" -type f ! -name '*.*' -print0 | xargs -0 -n1 basename)
[0 more errors; see full log]

Full log here.