Add ability to change particle type when regrowing

[brownd1978]

This PR provides an option to force regrown tracks to have a different particle type (mass) than what the KalSeed stores. The default is for regrown tracks to have the same particle type as the KalSeed.

[FNALbuild]

Hi @brownd1978,
You have proposed changes to files in these packages:

• Mu2eKinKal
• RecoDataProducts

which require these tests: build.

@Mu2e/write, @Mu2e/fnalbuild-users have access to CI actions on main.

⌛ The following tests have been triggered for 934d561: build (Build queue - API unavailable)

About FNALbuild. Code review on Mu2e/Offline.

[FNALbuild]

‼️ It was not possible to prepare the workspace for this test. This is often caused by merge conflicts - please check and try again.

> git diff --check | grep -i conflict
Mu2eKinKal/src/RegrowLoopHelix_module.cc:280: leftover conflict marker
Mu2eKinKal/src/RegrowLoopHelix_module.cc:283: leftover conflict marker
Mu2eKinKal/src/RegrowLoopHelix_module.cc:287: leftover conflict marker

Test	Result	Details
test with	✅	Command did not list any other PRs to include
merge	❌	934d561 into 20895af merge failed

[brownd1978]

@FNALbuild run build test

[FNALbuild]

⌛ The following tests have been triggered for a384c3d: build (Build queue - API unavailable)

[FNALbuild]

☀️ The build tests passed at a384c3d.

Test	Result	Details
test with	✅	Command did not list any other PRs to include
merge	✅	Merged a384c3d at 20895af
build (prof)	✅	Log file. Build time: 04 min 26 sec
ceSimReco	✅	Log file.
g4test_03MT	✅	Log file.
transportOnly	✅	Log file.
POT	✅	Log file.
g4study	✅	Log file.
cosmicSimReco	✅	Log file.
cosmicOffSpill	✅	Log file.
ceSteps	✅	Log file.
ceDigi	✅	Log file.
muDauSteps	✅	Log file.
ceMix	✅	Log file.
rootOverlaps	✅	Log file.
g4surfaceCheck	✅	Log file.
trigger	✅	Log file.
check_cmake	✅	Log file.
FIXME, TODO	➡️	TODO (0) FIXME (2) in 5 files
clang-tidy	➡️	4 errors 38 warnings
whitespace check	✅	no whitespace errors found

N.B. These results were obtained from a build of this Pull Request at a384c3d after being merged into the base branch at 20895af.

For more information, please check the job page here.
Build artifacts are deleted after 5 days. If this is not desired, select Keep this build forever on the job page.

[oksuzian]

PR Summary

Purpose: Adds an option to force regrown tracks to have a different particle type (mass) than what the KalSeed stores. Default behavior is unchanged (same particle type as the KalSeed).

• Scope: 7 files changed (+84, −27), no reviews yet, label build finished
• Risk: Low–medium — touches a shared reco data product (KalSeed/KalSegment) but changes are additive/backward-compatible via default arguments
• Mergeable: Likely; no blocking reviews present

Core Changes

1. KalSegment – trajectory converters (loopHelix, centralHelix, kinematicLine) now take an optional double mass = -1.0. Moved from inline header to .cc. When mass >= 0, they rebuild the ParticleStateEstimate with the overridden mass.
2. KalSeed – the three *FitTrajectory() methods now accept an optional PDGCode::type ptype = PDGCode::unknown; when set (and different from _tpart), they look up the mass via GlobalConstantsHandle<ParticleDataList> and pass it down.
3. RegrowLoopHelix_module – new optional fhicl parameter FitParticle (PDG code). Overrides the particle when building KKTRK, preserving the sign of the original kseed.particle().
4. Build files – add GlobalConstantsService dependency to RecoDataProducts (CMake + SConscript).

Issues Found

1. Behavior change unrelated to the PR's stated purpose (potential regression) — RecoDataProducts/src/KalSegment.cc

The t0 fallback was changed from a legacy computation to now throwing:

-    //      throw cet::exception(...)
-    // for now, revert to the legacy implementation...
-    auto vel = _pstate.velocity();
-    return _pstate.time() - _pstate.position3().Z()/vel.Z();
+    throw cet::exception("RECO")<<"mu2e::KalSegment: no trajectory specified in flag" << std::endl;

This converts a silent-fallback path into a hard exception. Any caller relying on the legacy behavior (e.g. segments without a trajectory flag set) will now throw. This is out of scope for "change particle type when regrowing" and deserves explicit callout / confirmation that no production path hits it.

2. Suspicious cast in the module — Mu2eKinKal/src/RegrowLoopHelix_module.cc

auto tpart = tpart_ != PDGCode::unknown ? static_cast<PDGCode>(std::copysign(...)) : kseed.particle();

static_cast<PDGCode> casts to the class/enum name PDGCode, whereas elsewhere the code uses PDGCode::type. If PDGCode is a struct wrapping an enum type, this may not compile or may be relying on an implicit conversion. Worth verifying it should be PDGCode::type.

3. Duplicate include — Mu2eKinKal/src/RegrowLoopHelix_module.cc

+#include "Offline/GlobalConstantsService/inc/GlobalConstantsHandle.hh"
+#include "Offline/GlobalConstantsService/inc/ParticleDataList.hh"

ParticleDataList.hh is already included at the top of the file (line 21 in the context shown). The second include is redundant.

4. Mass-lookup duplication — RecoDataProducts/src/KalSeed.cc

The identical 4-line mass-lookup block is copy-pasted into all three *FitTrajectory methods. Minor — a small private helper would reduce duplication and the risk of them diverging.

[FNALbuild]

📝 The HEAD of main has changed to eb6c796. Tests are now out of date.