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feat: Add option to split pions and kaons in run_fixedTarget #1063

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feat: Add option to split pions and kaons in run_fixedTarget #1063

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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ it in future.
## Unreleased

### Added
* Add option to split kaons and pions right before they decay, to increase the number of muons

### Changed

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16 changes: 12 additions & 4 deletions gconfig/g4Config.C
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Expand Up @@ -30,10 +30,18 @@ void Config() {
/// - stackPopper - stackPopper process
/// When more than one options are selected, they should be separated with '+'
/// character: eg. stepLimit+specialCuts.
TG4RunConfiguration* runConfiguration = new TG4RunConfiguration(
"geomRoot", "FTFP_BERT_HP_EMZ", "stepLimiter+specialCuts+specialControls",
false, // specialStacking (default)
false); // disable MT

const char* env = std::getenv("KAON_PION_SPLITS");
int32_t fNsplits = env ? std::atoi(env) : 0;

std::string controls = "stepLimiter+specialCuts+specialControls";
/// stackPopper is required when adding secondaries, e.g. when splitting the
/// pions and kaons
if (fNsplits != 0) controls += "+stackPopper";

@coderabbitai coderabbitai Bot Jun 23, 2026

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🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

Align stackPopper activation with positive split semantics.

At Line 40, fNsplits != 0 enables +stackPopper even for negative values, but downstream splitting paths are gated on fNsplits > 0. Use a strictly positive check to keep configuration behavior consistent.

🔧 Proposed fix 
-  if (fNsplits != 0) controls += "+stackPopper";
+  if (fNsplits > 0) controls += "+stackPopper";
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
if (fNsplits != 0) controls += "+stackPopper";
if (fNsplits > 0) controls += "+stackPopper";
🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@gconfig/g4Config.C` at line 40, The condition at line 40 that controls
stackPopper activation uses `fNsplits != 0`, which enables the feature for both
positive and negative split values, but the downstream splitting logic only
activates when `fNsplits > 0`. Change the condition from `fNsplits != 0` to
`fNsplits > 0` in the stackPopper control statement to ensure consistent
behavior and prevent stackPopper from being activated when actual splitting does
not occur.

TG4RunConfiguration* runConfiguration =
new TG4RunConfiguration("geomRoot", "FTFP_BERT_HP_EMZ", controls.c_str(),
false, // specialStacking (default)
false); // disable MT

/// Create the G4 VMC
TGeant4* geant4 =
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17 changes: 17 additions & 0 deletions macro/run_fixedTarget.py
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Expand Up @@ -78,6 +78,16 @@ def get_work_dir(run_number, tag: str | None = None) -> str:
ap.add_argument("-J", "--Jpsi-mainly", action=argparse.BooleanOptionalAction, dest="JpsiMainly", default=False)
ap.add_argument("-b", "--boostDiMuon", type=float, default=1.0, help="boost Di-muon branching ratios")
ap.add_argument("-X", "--boostFactor", type=float, default=1.0, help="boost Di-muon prod cross sections")
ap.add_argument(
"--kaon-pion-splits",
type=int,
default=0,
help="splitting factor for kaons and pions, in order to boost the number of muons stemming from their decays",
)
ap.add_argument(
"--multiple-kpi-splits", action="store_true", help="split kaons and pions multiple times along the track path"
)

Comment on lines +81 to +90

@coderabbitai coderabbitai Bot Jun 23, 2026

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🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

Validate split-flag combinations at parse time.

Lines 81-90 allow invalid combinations (e.g., negative --kaon-pion-splits, or --multiple-kpi-splits with zero splits), which currently fail silently at runtime. Add explicit argument validation right after parsing.

🔧 Proposed fix 
 args = ap.parse_args()
+if args.kaon_pion_splits < 0:
+    ap.error("--kaon-pion-splits must be >= 0")
+if args.multiple_kpi_splits and args.kaon_pion_splits == 0:
+    ap.error("--multiple-kpi-splits requires --kaon-pion-splits > 0")
🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@macro/run_fixedTarget.py` around lines 81 - 90, The argument parser currently
accepts invalid flag combinations without validation, such as negative values
for the kaon-pion-splits argument or using the multiple-kpi-splits flag with
zero splits, causing silent failures at runtime. After calling ap.parse_args()
to parse the command line arguments, add explicit validation to check that
kaon-pion-splits is non-negative and that if multiple-kpi-splits is True, then
kaon-pion-splits must be greater than zero. If either condition fails, raise an
appropriate error or print an error message and exit with a non-zero status
code.

ap.add_argument("-C", "--charm", action=argparse.BooleanOptionalAction, default=False, help="generate charm decays")
ap.add_argument("-B", "--beauty", action=argparse.BooleanOptionalAction, default=False, help="generate beauty decays")
ap.add_argument(
Expand Down Expand Up @@ -272,6 +282,8 @@ def get_work_dir(run_number, tag: str | None = None) -> str:
if args.boostFactor > 1:
# Turn off UseGeneralProcess to access GammaToMuons directly when cross-sections need to be changed
os.environ["SET_GENERAL_PROCESS_TO_FALSE"] = "1"
if args.kaon_pion_splits > 0:
os.environ["KAON_PION_SPLITS"] = str(args.kaon_pion_splits)
run.SetUserConfig("g4Config.C") # user configuration file default g4Config.C
rtdb = run.GetRuntimeDb()

Expand Down Expand Up @@ -342,6 +354,9 @@ def get_work_dir(run_number, tag: str | None = None) -> str:


sensPlaneHA = ROOT.exitHadronAbsorber()
sensPlaneHA.SetNSplits(args.kaon_pion_splits) # type: ignore[missing-attribute]
if args.multiple_kpi_splits:
sensPlaneHA.SetSplitMultipleTimes() # type: ignore[missing-attribute]
sensPlaneHA.SetEnergyCut(args.ecut * u.GeV)
sensPlaneHA.SetVetoPointName("PlaneHA")

Expand Down Expand Up @@ -422,6 +437,8 @@ def get_work_dir(run_number, tag: str | None = None) -> str:
fStack = gMC.GetStack()
fStack.SetMinPoints(1)
fStack.SetEnergyCut(-1.0)
if args.kaon_pion_splits > 0:
fStack.SetSplitting()
#
import AddDiMuonDecayChannelsToG4

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