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Add optional protonabsorber.zStartInMu2e: absolute IPA position #1913

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Add optional protonabsorber.zStartInMu2e: absolute IPA position #1913

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8 changes: 8 additions & 0 deletions GeometryService/src/MECOStyleProtonAbsorberMaker.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -125,6 +125,14 @@ namespace mu2e {
// we add space for the virtual detector here
double targetEnd = _target->centerInMu2e().z() + 0.5*_target->cylinderLength() + 2.*vdHL;;

// Optional absolute pinning: when protonabsorber.zStartInMu2e is set,
// the IPA's upstream end sits at that absolute z regardless of the
// stopping target; distFromTargetEnd then only anchors the cone-radius
// interpolation. Unset (default): stock target-relative behavior.
if ( _config.hasName("protonabsorber.zStartInMu2e") ) {
targetEnd = _config.getDouble("protonabsorber.zStartInMu2e") - distFromTargetEnd;

@AndrewEdmonds11 AndrewEdmonds11 Aug 3, 2026

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Does the distFromTargetEnd parameter still need to be set correctly? By default it is zero and so here the targetEnd would be the starting position of the IPA...

}

// distance from target end to ds2-ds3 boundary
double targetEndToDS2End = _ds->vac_zLocDs23Split() - targetEnd;

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3 changes: 3 additions & 0 deletions Mu2eG4/geom/protonAbsorber_cylindrical_v04.txt
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Expand Up @@ -29,6 +29,9 @@ bool protonabsorber.solid = false;
// To make inner part shorter than MECO design
bool protonabsorber.isShorterCone = true;
double protonabsorber.distFromTargetEnd = 625.; //mu2e z positions are 6901-7901 mm
// Optional: pin the IPA at an absolute z, independent of the stopping
// target (see MECOStyleProtonAbsorberMaker):
// double protonabsorber.zStartInMu2e = 6901.;
double protonabsorber.halfLength = 500.0;

bool protonabsorber.ipa.buildSupports = true;
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