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[PWGEM] PhotonMeson: Fix bug in EMNonLin #15137

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Merged
mhemmer-cern merged 1 commit into from
Feb 25, 2026
+26 −25
Merged

[PWGEM] PhotonMeson: Fix bug in EMNonLin #15137

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23 changes: 14 additions & 9 deletions PWGEM/PhotonMeson/Core/EMNonLin.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -25,22 +25,27 @@ float EMNonLin::getCorrectionFactor(float x, const Context& ctx)
return x;
}

float val = x;
// safety measure
int maxIter = std::min(ctx.nIter, MaxIter - 1);

float scale = 1.f; // cumulative scale
float refVal = x; // reference value for computing next scale

for (int i = 0; i <= maxIter; ++i) {
if (val == 0.f) {
if (refVal == 0.f) {
break;
}

float inv = 1.f / val;
val *= (1.f + ctx.params[i].par0 * inv +
ctx.params[i].par1 * inv * inv) /
(1.f + ctx.params[i].par2 * inv);
}
const auto& p = ctx.params[i];

return val;
// scale function (x + a + b/x)/(x + c) which goes towards 1 for large x since x >> a,b,c -> x/x = 1
float iterScale =
(refVal + p.par0 + p.par1 / refVal) /
(refVal + p.par2);

scale *= iterScale; // total scale = product over itertaion scale
refVal = x * scale; // next iteration uses scaled original input
}
return scale;
}

const EMNonLin::NonLinParams* EMNonLin::resolveParams(PhotonType type, float cent)
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28 changes: 12 additions & 16 deletions PWGEM/PhotonMeson/TableProducer/nonLinProducer.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -109,32 +109,30 @@ struct NonLinProducer {
template <o2::soa::is_table TClusters, o2::soa::is_iterator TCollisio>
void runEMC(TClusters const& clusters, TCollisio& collision)
{
float cent = getCentrality(collision);

int32_t collIndex = collision.globalIndex();
float cent = getCentrality(collision);
emNonLinContextEMC.setParams(emNonLinEMC.resolveParams(o2::pwgem::nonlin::EMNonLin::PhotonType::kEMC, cent));

for (const auto& cluster : clusters) {
float nonLinE = 0.f;
float nonLinPt = 0.f;
float nonLinFactor = 1.f;

// check that we are at the correct collision
if (cluster.emphotoneventId() != collIndex) {
collIndex = cluster.emphotoneventId();
collision.setCursor(collIndex);
cent = getCentrality(collision);
emNonLinContextEMC.setParams(emNonLinEMC.resolveParams(o2::pwgem::nonlin::EMNonLin::PhotonType::kEMC, cent));
}

emNonLinContextEMC.setParams(emNonLinEMC.resolveParams(o2::pwgem::nonlin::EMNonLin::PhotonType::kEMC, cent));

// fill before non lin histograms
historeg.fill(HIST("QA/EMC/EIn"), cluster.e());
historeg.fill(HIST("QA/EMC/PtIn"), cluster.pt());

// get NonLin factor from class dependent on the centrality
nonLinFactor = emNonLinEMC.getCorrectionFactor(cluster.e(), emNonLinContextEMC);
float nonLinFactor = emNonLinEMC.getCorrectionFactor(cluster.e(), emNonLinContextEMC);

nonLinE = nonLinFactor * cluster.e();
nonLinPt = nonLinFactor * cluster.pt();
float nonLinE = nonLinFactor * cluster.e();
float nonLinPt = nonLinFactor * cluster.pt();

// fill after non lin histograms
historeg.fill(HIST("QA/EMC/EOut"), nonLinE);
Expand All @@ -147,29 +145,27 @@ struct NonLinProducer {
template <o2::soa::is_table TV0, o2::soa::is_iterator TCollisio>
void runPCM(TV0 const& v0s, TCollisio& collision)
{
float cent = getCentrality(collision);

int32_t collIndex = collision.globalIndex();
float cent = getCentrality(collision);
emNonLinContextPCM.setParams(emNonLinPCM.resolveParams(o2::pwgem::nonlin::EMNonLin::PhotonType::kPCM, cent));
for (const auto& v0 : v0s) {
float nonLinPt = 0.f;
float nonLinFactor = 1.f;

// check that we are at the correct collision
if (v0.emphotoneventId() != collIndex) {
collIndex = v0.emphotoneventId();
collision.setCursor(collIndex);
cent = getCentrality(collision);
emNonLinContextPCM.setParams(emNonLinPCM.resolveParams(o2::pwgem::nonlin::EMNonLin::PhotonType::kPCM, cent));
}

emNonLinContextPCM.setParams(emNonLinPCM.resolveParams(o2::pwgem::nonlin::EMNonLin::PhotonType::kPCM, cent));

// fill before non lin histograms
historeg.fill(HIST("QA/PCM/PtIn"), v0.pt());

// get NonLin factor from class dependent on the centrality
nonLinFactor = emNonLinEMC.getCorrectionFactor(v0.pt(), emNonLinContextPCM);
float nonLinFactor = emNonLinEMC.getCorrectionFactor(v0.pt(), emNonLinContextPCM);

nonLinPt = nonLinFactor * v0.pt();
float nonLinPt = nonLinFactor * v0.pt();

// fill after non lin histograms
historeg.fill(HIST("QA/PCM/PtOut"), nonLinPt);
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