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Fix mother -> daughter indices in case of replacement in HF gerator #2017

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Merged
fgrosa merged 1 commit into from
Jun 1, 2025
Merged

Fix mother -> daughter indices in case of replacement in HF gerator #2017

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53 changes: 47 additions & 6 deletions MC/config/PWGHF/external/generator/generator_pythia8_gaptriggered_hf.C
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Original file line number Diff line number Diff line change
Expand Up @@ -184,7 +184,6 @@ protected:

for (auto iPart{0}; iPart < mPythia.event.size(); ++iPart)
{

// search for Q-Qbar mother with at least one Q in rapidity window
if (!isGoodAtPartonLevel)
{
Expand Down Expand Up @@ -254,7 +253,7 @@ protected:

bool replaceParticle(int iPartToReplace, int pdgCodeNew) {

std::array<int, 2> mothers = {mPythia.event[iPartToReplace].mother1(), mPythia.event[iPartToReplace].mother2()};
auto mothers = mPythia.event[iPartToReplace].motherList();

std::array<int, 25> pdgDiquarks = {1103, 2101, 2103, 2203, 3101, 3103, 3201, 3203, 3303, 4101, 4103, 4201, 4203, 4301, 4303, 4403, 5101, 5103, 5201, 5203, 5301, 5303, 5401, 5403, 5503};

Expand Down Expand Up @@ -288,15 +287,57 @@ protected:
}
float energy = std::sqrt(px*px + py*py + pz*pz + mass*mass);

// buffer daughter indices of mothers
std::vector<std::vector<int>> dauOfMothers{};
for (auto const& mother: mothers) {
dauOfMothers.push_back(mPythia.event[mother].daughterList());
}

// we remove particle to replace and its daughters
mPythia.event[iPartToReplace].undoDecay();
mPythia.event.remove(iPartToReplace, iPartToReplace, true); // we remove the original particle

int status = std::abs(mPythia.event[iPartToReplace].status());
int status = std::abs(mPythia.event[iPartToReplace].status()); // we must get it here otherwise it is negative (already decayed)
if (status < 81 || status > 89) {
status = 81;
}
mPythia.event.append(charge * pdgCodeNew, status, mothers[0], mothers[1], 0, 0, 0, 0, px, py, pz, energy, mass);
mPythia.event.remove(iPartToReplace, iPartToReplace, true); // we remove the original particle

// we restore the daughter indices of the mothers after the removal
int newPartIdx{0};
std::array<int, 2> newMothers = {0, 0};
if (mGenConfig.includePartonEvent) { // only necessary in case of parton event, otherwise we keep no mother
newMothers[0] = mothers.front();
newMothers[1] = mothers.back();
newPartIdx = mPythia.event.size();
}
for (auto iMom{0u}; iMom<mothers.size(); ++iMom) {
auto dau1 = dauOfMothers[iMom].front();
auto dau2 = dauOfMothers[iMom].back();
if (dau2 > dau1) {
mPythia.event[mothers[iMom]].daughter1(dau1);
mPythia.event[mothers[iMom]].daughter2(dau2 - 1);
} else if (dau1 == dau2) {
if (dau1 == 0) {
mPythia.event[mothers[iMom]].daughter1(0);
mPythia.event[mothers[iMom]].daughter2(0);
} else { // in this case we set it equal to the new particle
mPythia.event[mothers[iMom]].daughter1(newPartIdx);
mPythia.event[mothers[iMom]].daughter2(newPartIdx);
}
} else if (dau2 < dau1) { // in this case we set it equal to the new particle
if (dau2 == 0) {
mPythia.event[mothers[iMom]].daughter1(newPartIdx);
} else {
if (dau1 == iPartToReplace) {
mPythia.event[mothers[iMom]].daughter1(newPartIdx);
} else {
mPythia.event[mothers[iMom]].daughter2(newPartIdx);
}
}
}
auto dauOfMomUp = mPythia.event[mothers[iMom]].daughterList();
}

mPythia.event.append(charge * pdgCodeNew, status, newMothers[0], newMothers[1], 0, 0, 0, 0, px, py, pz, energy, mass);
mPythia.moreDecays(); // we need to decay the new particle

return true;
Expand Down