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[PWGCF] Enhance lambda spin polarization analysis with mixing #14420

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prchakra merged 2 commits into from
Jan 7, 2026
+89 −12
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[PWGCF] Enhance lambda spin polarization analysis with mixing #14420

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49b3094
Enhance lambda spin polarization analysis with mixing
subhadee-ali Jan 7, 2026
67ff9b3
Introduce configurable limits for kinematic matching
subhadee-ali Jan 7, 2026
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101 changes: 89 additions & 12 deletions PWGCF/TwoParticleCorrelations/Tasks/lambdaSpinPolarization.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -1543,9 +1543,16 @@ struct LambdaSpinPolarization {
Configurable<int> cNPhiBins{"cNPhiBins", 36, "N Phi Bins"};
Configurable<int> cNBinsCosTS{"cNBinsCosTS", 10, "N CosTS Bins"};
Configurable<bool> cInvBoostFlag{"cInvBoostFlag", true, "Inverse Boost Flag"};
Configurable<int> mixingParameter{"mixingParameter", 5, "How many events are mixed"};

// Centrality Axis
ConfigurableAxis cMultBins{"cMultBins", {VARIABLE_WIDTH, 0.0f, 10.0f, 30.0f, 50.f, 80.0f, 100.f}, "Variable Mult-Bins"};
ConfigurableAxis axisCentME{"axisCentME", {VARIABLE_WIDTH, 0, 10, 30, 50, 100}, "Mixing bins - centrality (%)"};
ConfigurableAxis axisVtxZME{"axisVtxZME", {VARIABLE_WIDTH, -7, -3, 0, 3, 7}, "Mixing bins - z-vertex"};

Configurable<float> cMaxDeltaPt{"cMaxDeltaPt", 0.1f, "Max delta pT for kinematic matching (GeV/c)"};
Configurable<float> cMaxDeltaPhi{"cMaxDeltaPhi", 0.1f, "Max delta phi for kinematic matching (rad)"};
Configurable<float> cMaxDeltaRap{"cMaxDeltaRap", 0.1f, "Max delta rapidity for kinematic matching"};

// Histogram Registry.
HistogramRegistry histos{"histos", {}, OutputObjHandlingPolicy::AnalysisObject};
Expand All @@ -1570,8 +1577,14 @@ struct LambdaSpinPolarization {
const AxisSpec axisCosTS(cNBinsCosTS, -1, 1, "cos(#theta*)");
const AxisSpec axisDR(10, 0, 2, "#DeltaR");

// Single and Two Particle Densities
// 1D Histograms
// Pool occupancy
histos.add("QA/ME/hPoolCentVz", "ME pool occupancy;centrality (%);V_{z} (cm)", kTH2F, {axisCentME, axisVtxZME});

// Lambda multiplicity vs centrality
histos.add("QA/ME/hLambdaMultVsCent", "ME #Lambda multiplicity;centrality (%);N_{#Lambda}", kTH2F, {axisCentME, {50, 0, 50}});
histos.add("QA/ME/hAntiLambdaMultVsCent", "ME #bar{#Lambda} multiplicity;centrality (%);N_{#bar{#Lambda}}", kTH2F, {axisCentME, {50, 0, 50}});

// inv mass vs pt for Lambda and AntiLambda
histos.add("Reco/h2f_n2_mass_LaPLaM", "m_{inv}^{#Lambda} vs m_{inv}^{#bar{#Lambda}}", kTHnSparseF, {axisMass, axisMass, axisPt, axisPt});
histos.add("Reco/h2f_n2_mass_LaPLaP", "m_{inv}^{#Lambda} vs m_{inv}^{#Lambda}", kTHnSparseF, {axisMass, axisMass, axisPt, axisPt});
histos.add("Reco/h2f_n2_mass_LaMLaM", "m_{inv}^{#bar{#Lambda}} vs m_{inv}^{#bar{#Lambda}}", kTHnSparseF, {axisMass, axisMass, axisPt, axisPt});
Expand All @@ -1583,9 +1596,6 @@ struct LambdaSpinPolarization {
histos.add("RecoCorr/h2f_n2_ctheta_LaPLaM", "#rho_{2}^{#Lambda#bar{#Lambda}}", kTHnSparseF, {axisCent, axisDRap, axisDPhi, axisCosTS});
histos.add("RecoCorr/h2f_n2_ctheta_LaPLaP", "#rho_{2}^{#Lambda#Lambda}", kTHnSparseF, {axisCent, axisDRap, axisDPhi, axisCosTS});
histos.add("RecoCorr/h2f_n2_ctheta_LaMLaM", "#rho_{2}^{#bar{#Lambda}#bar{#Lambda}}", kTHnSparseF, {axisCent, axisDRap, axisDPhi, axisCosTS});
// histos.add("RecoCorr/h2f_n2_dphi_LaPLaM", "#rho_{2}^{#Lambda#bar{#Lambda}}", kTHnSparseF, {axisCent, axisDRap, axisDPhi, axisDPhi});
// histos.add("RecoCorr/h2f_n2_dphi_LaPLaP", "#rho_{2}^{#Lambda#Lambda}", kTHnSparseF, {axisCent, axisDRap, axisDPhi, axisDPhi});
// histos.add("RecoCorr/h2f_n2_dphi_LaMLaM", "#rho_{2}^{#bar{#Lambda}#bar{#Lambda}}", kTHnSparseF, {axisCent, axisDRap, axisDPhi, axisDPhi});
}

void getBoostVector(std::array<float, 4> const& p, std::array<float, 3>& v, bool inverseBoostFlag = true)
Expand Down Expand Up @@ -1619,7 +1629,7 @@ struct LambdaSpinPolarization {
static constexpr std::string_view SubDirHist[] = {"LaPLaM", "LaPLaP", "LaMLaM"};

// Fill lambda pair mass
histos.fill(HIST("Reco/h2f_n2_mass_") + HIST(SubDirHist[part_pair]), p1.mass(), p2.mass(), p1.pt(), p2.pt());
// histos.fill(HIST("Reco/h2f_n2_mass_") + HIST(SubDirHist[part_pair]), p1.mass(), p2.mass(), p1.pt(), p2.pt());
float drap = p1.rap() - p2.rap();
float dphi = RecoDecay::constrainAngle(p1.phi() - p2.phi(), -PI);
float dR = std::sqrt(drap * drap + dphi * dphi);
Expand All @@ -1638,11 +1648,7 @@ struct LambdaSpinPolarization {
std::array<float, 3> pr1tv = {pr1[0], pr1[1], pr1[2]};
std::array<float, 3> pr2tv = {pr2[0], pr2[1], pr2[2]};
float ctheta = RecoDecay::dotProd(pr1tv, pr2tv) / (RecoDecay::sqrtSumOfSquares(pr1tv[0], pr1tv[1], pr1tv[2]) * RecoDecay::sqrtSumOfSquares(pr2tv[0], pr2tv[1], pr2tv[2]));
// float prdphi = RecoDecay::constrainAngle(RecoDecay::phi(pr1) - RecoDecay::phi(pr2), -PI);
// float prdrap = RecoDecay::eta(pr1tv) - RecoDecay::eta(pr2tv);

// Fill pair density
// histos.fill(HIST("RecoCorr/h2f_n2_dphi_") + HIST(SubDirHist[part_pair]), cent, drap, dphi, prdphi);
histos.fill(HIST("RecoCorr/h2f_n2_ctheta_") + HIST(SubDirHist[part_pair]), cent, drap, dphi, ctheta);
histos.fill(HIST("RecoCorr/h2f_n2_dltaR_") + HIST(SubDirHist[part_pair]), cent, dR, ctheta);
}
Expand All @@ -1661,10 +1667,33 @@ struct LambdaSpinPolarization {
}
}

template <ParticlePairType part_pair, bool samelambda, typename T>
void analyzePairsWithKinematicMatching(T const& trks_1, T const& trks_2)
{
for (auto const& trk_1 : trks_1) {
for (auto const& trk_2 : trks_2) {
if (samelambda && ((trk_1.index() == trk_2.index()))) {
continue;
}

// Kinematic matching with named constants
float deltaPt = std::abs(trk_1.pt() - trk_2.pt());
float deltaPhi = std::abs(RecoDecay::constrainAngle(trk_1.phi() - trk_2.phi(), -PI));
float deltaRap = std::abs(trk_1.rap() - trk_2.rap());

if (deltaPt < cMaxDeltaPt && deltaPhi < cMaxDeltaPhi && deltaRap < cMaxDeltaRap) {
fillPairHistos<part_pair>(trk_1, trk_2);
}
}
}
}

// Initialize tables
using LambdaCollisions = aod::LambdaCollisions;
using LambdaTracks = soa::Join<aod::LambdaTracks, aod::LambdaTracksExt>;

Preslice<LambdaTracks> perCollisionLambda = aod::lambdatrack::lambdaCollisionId;

SliceCache cache;
Partition<LambdaTracks> partLambdaTracks = (aod::lambdatrack::v0Type == (int8_t)kLambda) && (aod::lambdatrackext::trueLambdaFlag == true) && (aod::lambdatrack::v0PrmScd == (int8_t)kPrimary);
Partition<LambdaTracks> partAntiLambdaTracks = (aod::lambdatrack::v0Type == (int8_t)kAntiLambda) && (aod::lambdatrackext::trueLambdaFlag == true) && (aod::lambdatrack::v0PrmScd == (int8_t)kPrimary);
Expand All @@ -1689,7 +1718,55 @@ struct LambdaSpinPolarization {
analyzePairs<kAntiLambdaAntiLambda, true>(antiLambdaTracks, antiLambdaTracks);
}

PROCESS_SWITCH(LambdaSpinPolarization, processDataReco, "Process for Data and MCReco", true);
PROCESS_SWITCH(LambdaSpinPolarization, processDataReco, "Process for Data and MCReco", false);

struct GetMultiplicity {
float operator()(auto const& col) const
{
return col.cent();
}
};

using MixedBinning = FlexibleBinningPolicy<std::tuple<GetMultiplicity>, o2::aod::collision::PosZ, GetMultiplicity>;
MixedBinning binningOnVtxAndMult{
{GetMultiplicity{}},
{axisVtxZME, axisCentME},
true};

void processDataRecoMixed(LambdaCollisions const& col, LambdaTracks const&)
{
for (auto const& [col1, col2] : soa::selfCombinations(binningOnVtxAndMult, mixingParameter, -1, col, col)) {

if (col1.globalIndex() == col2.globalIndex()) {
continue;
}

cent = col1.cent();

// QA: pool occupancy
histos.fill(HIST("QA/ME/hPoolCentVz"), col1.cent(), col1.posZ());

// Lambda slices
auto lambdaTracks_col1 = partLambdaTracks->sliceByCached(aod::lambdatrack::lambdaCollisionId, col1.globalIndex(), cache);
auto lambdaTracks_col2 = partLambdaTracks->sliceByCached(aod::lambdatrack::lambdaCollisionId, col2.globalIndex(), cache);

// Anti-lambda slices
auto antiLambdaTracks_col1 = partAntiLambdaTracks->sliceByCached(aod::lambdatrack::lambdaCollisionId, col1.globalIndex(), cache);
auto antiLambdaTracks_col2 = partAntiLambdaTracks->sliceByCached(aod::lambdatrack::lambdaCollisionId, col2.globalIndex(), cache);

// QA: multiplicities
histos.fill(HIST("QA/ME/hLambdaMultVsCent"), col1.cent(), lambdaTracks_col1.size());
histos.fill(HIST("QA/ME/hAntiLambdaMultVsCent"), col1.cent(), antiLambdaTracks_col1.size());

// Mixed-event pairs
analyzePairsWithKinematicMatching<kLambdaAntiLambda, false>(lambdaTracks_col1, antiLambdaTracks_col2);
analyzePairsWithKinematicMatching<kLambdaAntiLambda, false>(antiLambdaTracks_col1, lambdaTracks_col2);
analyzePairsWithKinematicMatching<kLambdaLambda, true>(lambdaTracks_col1, lambdaTracks_col2);
analyzePairsWithKinematicMatching<kAntiLambdaAntiLambda, true>(antiLambdaTracks_col1, antiLambdaTracks_col2);
}
}

PROCESS_SWITCH(LambdaSpinPolarization, processDataRecoMixed, "Process for Data and MCReco for Mixed events", true);

void processDataRecoMixEvent(LambdaCollisions::iterator const& collision, LambdaTracks const& tracks)
{
Expand All @@ -1707,7 +1784,7 @@ struct LambdaSpinPolarization {
}
}

PROCESS_SWITCH(LambdaSpinPolarization, processDataRecoMixEvent, "Process for Data and MCReco Mix Event", true);
PROCESS_SWITCH(LambdaSpinPolarization, processDataRecoMixEvent, "Process for Data and MCReco Mix Event", false);
};

WorkflowSpec defineDataProcessing(ConfigContext const& cfgc)
Expand Down
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