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[PWGEM] add switchable crossed-pair (leg-swap) veto with QA #17215

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Merged
mhemmer-cern merged 4 commits into from
Jul 27, 2026
+128 −2
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[PWGEM] add switchable crossed-pair (leg-swap) veto with QA #17215

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48d5d76
add switchable crossed-pair (leg-swap) veto with QA to avoid signal f…
Steffimro Jul 27, 2026
7a9a4c7
fix o2-linter errors
Steffimro Jul 27, 2026
2123949
fix bracket notation for o2-linter
Steffimro Jul 27, 2026
af193f4
fix bracket notation
Steffimro Jul 27, 2026
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130 changes: 128 additions & 2 deletions PWGEM/PhotonMeson/Tasks/photonhbt.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -149,6 +149,11 @@ struct Photonhbt {
float u{999.f};
};

struct CrossObs {
std::array<float, 2> mee{999.f, 999.f}; // crossed m(e+e-) per combo
std::array<float, 2> dist{999.f, 999.f}; // crossed line-line distance (cm)
};

struct TruthGamma {
int id = -1, posId = -1, negId = -1;
float eta = 0.f, phi = 0.f, pt = 0.f;
Expand Down Expand Up @@ -336,6 +341,15 @@ struct Photonhbt {
Configurable<float> cfgUCut{"cfgUCut", 0.f, "min u (sigma units); pairs with u < cut rejected in SE AND ME"};
} pairsep;

struct : ConfigurableGroup {
std::string prefix = "crosspair_group";
Configurable<bool> cfgDoCrossPairQA{"cfgDoCrossPairQA", false, "fill crossed-hypothesis QA (mee_cross, dist_cross vs qinv) for pairs passing all other pair cuts; SE and ME"};
Configurable<bool> cfgDoCrossPairCut{"cfgDoCrossPairCut", false, "reject pairs with a photon-like crossed combination; applied to SE AND ME"};
Configurable<float> cfgCrossMaxMee{"cfgCrossMaxMee", 0.04f, "veto: crossed m_ee below this (GeV/c^2)"};
Configurable<float> cfgCrossMaxDist{"cfgCrossMaxDist", 1.0f, "veto: crossed line-line distance below this (cm)"};
Configurable<float> cfgCrossMaxQinvQA{"cfgCrossMaxQinvQA", 0.3f, "fill crossed QA sparses only below this qinv"};
} crosspair;

struct : ConfigurableGroup {
std::string prefix = "eventcut_group";
Configurable<float> cfgZvtxMin{"cfgZvtxMin", -10.f, "min. Zvtx"};
Expand Down Expand Up @@ -656,6 +670,7 @@ struct Photonhbt {
addEventHistograms();
addPairCFHistograms();
addPairSepHistograms();
addCrossPairHistograms();
addSinglePhotonQAHistograms();
addPairQAHistograms();

Expand Down Expand Up @@ -704,8 +719,6 @@ struct Photonhbt {

fRegistryCF.add("Pair/mix/hDiffBC", "diff. global BC in mixed event;|BC_{current}-BC_{mixed}|", kTH1D, {{10001, -0.5, 10000.5}}, true);
}

// ─── CF: PairSep ────────────────────────
// ─── CF: PairSep ────────────────────────
void addPairSepHistograms()
{
Expand All @@ -717,6 +730,21 @@ struct Photonhbt {
}
}

void addCrossPairHistograms()
{
if (!(crosspair.cfgDoCrossPairQA.value || crosspair.cfgDoCrossPairCut.value)) {
return;
}
for (const auto& sm : {std::string("Pair/same/CrossPair/"), std::string("Pair/mix/CrossPair/")}) {
fRegistryCF.add((sm + "hSparse_Mee_Dist_Qinv").c_str(),
"crossed-hypothesis QA;m_{ee}^{cross} (GeV/c^{2});crossed line distance (cm);q_{inv} (GeV/c)",
kTHnSparseF, {{100, 0.f, 0.1f}, {100, 0.f, 10.f}, {60, 0.f, 0.3f}}, true);
auto h = fRegistryCF.add<TH1>((sm + "hVetoCounter").c_str(), "crossed-pair veto;;pairs", kTH1D, {{2, -0.5f, 1.5f}}, true);
h->GetXaxis()->SetBinLabel(1, "evaluated");
h->GetXaxis()->SetBinLabel(2, "vetoed");
}
}

// ─── pairQA: single-photon QA per cut step ─────────────────────────────────
void addSinglePhotonQAHistograms()
{
Expand Down Expand Up @@ -1246,6 +1274,72 @@ struct Photonhbt {
return s.u > pairsep.cfgUCut.value;
}

[[nodiscard]] static float lineLineDistance(std::array<float, 3> const& o1, std::array<float, 3> const& d1,
std::array<float, 3> const& o2, std::array<float, 3> const& d2)
{
const std::array<float, 3> w = {o2[0] - o1[0], o2[1] - o1[1], o2[2] - o1[2]};
const std::array<float, 3> n = {d1[1] * d2[2] - d1[2] * d2[1],
d1[2] * d2[0] - d1[0] * d2[2],
d1[0] * d2[1] - d1[1] * d2[0]};
const float nMag = std::sqrt(n[0] * n[0] + n[1] * n[1] + n[2] * n[2]);
const float d1Mag2 = d1[0] * d1[0] + d1[1] * d1[1] + d1[2] * d1[2];
if (nMag < 1e-6f * d1Mag2) { // o2-linter: disable=magic-number (near-parallel: point-to-line distance)
const float wDotD = (w[0] * d1[0] + w[1] * d1[1] + w[2] * d1[2]) / d1Mag2;
const std::array<float, 3> perp = {w[0] - wDotD * d1[0], w[1] - wDotD * d1[1], w[2] - wDotD * d1[2]};
return std::sqrt(perp[0] * perp[0] + perp[1] * perp[1] + perp[2] * perp[2]);
}
return std::fabs(w[0] * n[0] + w[1] * n[1] + w[2] * n[2]) / nMag;
}

[[nodiscard]] CrossObs computeCrossObs(PhotonWithLegs const& a, PhotonWithLegs const& b) const
{
constexpr float kMe = 0.000510999f; // electron mass, GeV/c^2
CrossObs c;
auto legVec = [](PhotonWithLegs const& p, int i) {
return ROOT::Math::PtEtaPhiMVector(p.fLegPt[i], p.fLegEta[i], p.fLegPhi[i], kMe);
};
auto legDir = [](PhotonWithLegs const& p, int i) -> std::array<float, 3> {
return {p.fLegPt[i] * std::cos(p.fLegPhi[i]), p.fLegPt[i] * std::sin(p.fLegPhi[i]),
p.fLegPt[i] * std::sinh(p.fLegEta[i])};
};
// Leg index 0 = e+, 1 = e- (makePhotonWithLegs filling order).
// Combo 0: a's e+ with b's e-. Combo 1: b's e+ with a's e-.
for (int combo = 0; combo < 2; ++combo) { // o2-linter: disable=magic-number (combinations of fake photons)
PhotonWithLegs const& pPos = (combo == 0) ? a : b;
PhotonWithLegs const& pEle = (combo == 0) ? b : a;
c.mee[combo] = static_cast<float>((legVec(pPos, 0) + legVec(pEle, 1)).M());
c.dist[combo] = lineLineDistance({pPos.fVx, pPos.fVy, pPos.fVz}, legDir(pPos, 0),
{pEle.fVx, pEle.fVy, pEle.fVz}, legDir(pEle, 1));
}
return c;
}

[[nodiscard]] inline bool passCrossPairVeto(CrossObs const& c) const
{
if (!crosspair.cfgDoCrossPairCut.value) {
return true;
}
for (int i = 0; i < 2; ++i) { // o2-linter: disable=magic-number (combinations of fake photons)
if (c.mee[i] < crosspair.cfgCrossMaxMee.value && c.dist[i] < crosspair.cfgCrossMaxDist.value) {
return false;
}
}
return true;
}

template <int ev_id>
inline void fillCrossPair(CrossObs const& c, float qinv, bool vetoed)
{
constexpr auto dir = (ev_id == 0) ? "Pair/same/CrossPair/" : "Pair/mix/CrossPair/";
fRegistryCF.fill(HIST(dir) + HIST("hVetoCounter"), vetoed ? 1.0 : 0.0);
if (qinv > crosspair.cfgCrossMaxQinvQA.value) {
return;
}
for (int i = 0; i < 2; ++i) { // o2-linter: disable=magic-number (combinations of fake photons)
fRegistryCF.fill(HIST(dir) + HIST("hSparse_Mee_Dist_Qinv"), c.mee[i], c.dist[i], qinv);
}
}

[[nodiscard]] float uTrue(TruthGamma const& g1, TruthGamma const& g2) const
{
const float sE = pairsep.cfgUSigEta.value, sP = pairsep.cfgUSigPhi.value;
Expand Down Expand Up @@ -1913,6 +2007,14 @@ struct Photonhbt {
if (isInsideEllipse(obs.deta, obs.dphi)) {
continue;
}
if (crosspair.cfgDoCrossPairQA.value || crosspair.cfgDoCrossPairCut.value) {
const auto cross = computeCrossObs(pwl1, pwl2);
const bool vetoed = !passCrossPairVeto(cross);
fillCrossPair<0>(cross, obs.qinv, vetoed);
if (vetoed) {
continue;
}
}

// ───after pair cuts ──────────────────────────────────────
fillPairSep<0, true>(sep, obs);
Expand Down Expand Up @@ -2000,6 +2102,14 @@ struct Photonhbt {
if (isInsideEllipse(obs.deta, obs.dphi)) {
continue;
}
if (crosspair.cfgDoCrossPairQA.value || crosspair.cfgDoCrossPairCut.value) {
const auto cross = computeCrossObs(g1, g2);
const bool vetoed = !passCrossPairVeto(cross);
fillCrossPair<1>(cross, obs.qinv, vetoed);
if (vetoed) {
continue;
}
}

fillPairSep<1, true>(sep, obs);
if (doQA) {
Expand Down Expand Up @@ -2122,6 +2232,14 @@ struct Photonhbt {
if (isInsideEllipse(obs.deta, obs.dphi)) {
continue;
}
if (crosspair.cfgDoCrossPairQA.value || crosspair.cfgDoCrossPairCut.value) {
const auto cross = computeCrossObs(pwl1, pwl2);
const bool vetoed = !passCrossPairVeto(cross);
fillCrossPair<0>(cross, obs.qinv, vetoed);
if (vetoed) {
continue;
}
}

// ─── after pair cuts ──────────────────────────────────────
fillPairSep<0, true>(sep, obs);
Expand Down Expand Up @@ -2260,6 +2378,14 @@ struct Photonhbt {
if (isInsideEllipse(obs.deta, obs.dphi)) {
continue;
}
if (crosspair.cfgDoCrossPairQA.value || crosspair.cfgDoCrossPairCut.value) {
const auto cross = computeCrossObs(g1, g2);
const bool vetoed = !passCrossPairVeto(cross);
fillCrossPair<1>(cross, obs.qinv, vetoed);
if (vetoed) {
continue;
}
}

// ─after pair cuts ──────────────────────────────────
fillPairSep<1, true>(sep, obs);
Expand Down
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