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Merge pull request #114 from rest-for-physics/mariajmz_diffusion
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TRestDetectorElectronDiffusionProcess taking into account the fano factor
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@lobis
lobis authored May 13, 2024
2 parents c1a601b + 11af6fb commit 5d4427f
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Showing 2 changed files with 52 additions and 32 deletions.
10 changes: 6 additions & 4 deletions inc/TRestDetectorElectronDiffusionProcess.h
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Original file line number Diff line number Diff line change
Expand Up @@ -39,13 +39,15 @@ class TRestDetectorElectronDiffusionProcess : public TRestEventProcess {
Double_t fAttachment;
Double_t fGasPressure;
Double_t fWValue;
Double_t fFanoFactor;
Double_t fLongitudinalDiffusionCoefficient;
Double_t fTransversalDiffusionCoefficient;
Bool_t fPoissonElectronExcitation;
Bool_t fUnitElectronEnergy;
UInt_t fMaxHits;
Double_t fSeed = 0;
UInt_t fSeed = 0;
Bool_t fCheckIsInside = true;
Bool_t fUseFanoFactor = false;
Bool_t fPoissonElectronExcitation = false;

public:
RESTValue GetInputEvent() const override { return fInputHitsEvent; }
Expand All @@ -61,7 +63,7 @@ class TRestDetectorElectronDiffusionProcess : public TRestEventProcess {
BeginPrintProcess();

RESTMetadata << " eField : " << fElectricField * units("V/cm") << " V/cm" << RESTendl;
RESTMetadata << " attachment coeficient : " << fAttachment << " V/cm" << RESTendl;
RESTMetadata << " attachment coefficient : " << fAttachment << " V/cm" << RESTendl;
RESTMetadata << " gas pressure : " << fGasPressure << " atm" << RESTendl;
RESTMetadata << " longitudinal diffusion coefficient : " << fLongitudinalDiffusionCoefficient
<< " cm^1/2" << RESTendl;
Expand Down Expand Up @@ -90,7 +92,7 @@ class TRestDetectorElectronDiffusionProcess : public TRestEventProcess {
// Destructor
~TRestDetectorElectronDiffusionProcess();

ClassDefOverride(TRestDetectorElectronDiffusionProcess, 4); // Template for a REST "event process" class
ClassDefOverride(TRestDetectorElectronDiffusionProcess, 5); // Template for a REST "event process" class
// inherited from TRestEventProcess
};
#endif
74 changes: 46 additions & 28 deletions src/TRestDetectorElectronDiffusionProcess.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,7 @@ void TRestDetectorElectronDiffusionProcess::Initialize() {
fTransversalDiffusionCoefficient = 0;
fLongitudinalDiffusionCoefficient = 0;
fWValue = 0;
fFanoFactor = 0;

fOutputHitsEvent = new TRestDetectorHitsEvent();
fInputHitsEvent = nullptr;
Expand Down Expand Up @@ -96,14 +97,25 @@ void TRestDetectorElectronDiffusionProcess::InitProcess() {
<< RESTendl;
exit(1);
#endif
if (fGasPressure <= 0) fGasPressure = fGas->GetPressure();
if (fElectricField <= 0) fElectricField = fGas->GetElectricField();
if (fWValue <= 0) fWValue = fGas->GetWvalue();

if (fGasPressure <= 0) {
fGasPressure = fGas->GetPressure();
}
fGas->SetPressure(fGasPressure);

if (fElectricField <= 0) {
fElectricField = fGas->GetElectricField();
}
fGas->SetElectricField(fElectricField);

if (fWValue <= 0) {
fWValue = fGas->GetWvalue();
}
fGas->SetW(fWValue);

if (fFanoFactor <= 0) {
fFanoFactor = fGas->GetGasFanoFactor();
}

if (fLongitudinalDiffusionCoefficient <= 0) {
fLongitudinalDiffusionCoefficient = fGas->GetLongitudinalDiffusion();
} // (cm)^1/2
Expand All @@ -124,8 +136,8 @@ TRestEvent* TRestDetectorElectronDiffusionProcess::ProcessEvent(TRestEvent* inpu
fInputHitsEvent = (TRestDetectorHitsEvent*)inputEvent;
fOutputHitsEvent->SetEventInfo(fInputHitsEvent);

set<unsigned int> hitsToProcess; // indices of the hits to process (we do not want to process veto hits)
for (unsigned int n = 0; n < fInputHitsEvent->GetNumberOfHits(); n++) {
set<int> hitsToProcess; // indices of the hits to process (we do not want to process veto hits)
for (int n = 0; n < static_cast<int>(fInputHitsEvent->GetNumberOfHits()); n++) {
if (fInputHitsEvent->GetType(n) == REST_HitType::VETO) {
// keep unprocessed hits as they are
fOutputHitsEvent->AddHit(fInputHitsEvent->GetX(n), fInputHitsEvent->GetY(n),
Expand All @@ -148,7 +160,7 @@ TRestEvent* TRestDetectorElectronDiffusionProcess::ProcessEvent(TRestEvent* inpu
bool isAttached;

Double_t wValue = fWValue;
const unsigned int totalElectrons = totalEnergy * REST_Units::eV / wValue;
const auto totalElectrons = static_cast<unsigned int>(totalEnergy * REST_Units::eV / wValue);

// TODO: double check this
if (fMaxHits > 0 && totalElectrons > fMaxHits) {
Expand Down Expand Up @@ -185,15 +197,21 @@ TRestEvent* TRestDetectorElectronDiffusionProcess::ProcessEvent(TRestEvent* inpu

Double_t driftDistance = plane->GetDistanceTo({x, y, z});

Int_t numberOfElectrons;
if (fPoissonElectronExcitation) {
numberOfElectrons = fRandom->Poisson(energy * REST_Units::eV / fWValue);
if (wValue != fWValue) {
// reduce the number of electrons to improve speed
numberOfElectrons = numberOfElectrons * fWValue / wValue;
double numberOfElectrons = energy * REST_Units::eV / wValue;
if (fUseFanoFactor) {
if (fFanoFactor <= 0) {
throw runtime_error("Fano factor not valid");
}
} else {
numberOfElectrons = energy * REST_Units::eV / wValue;
const auto sigma = TMath::Sqrt(fFanoFactor * numberOfElectrons);
numberOfElectrons = fRandom->Gaus(numberOfElectrons, sigma);
} else if (fPoissonElectronExcitation) {
// this is probably a bad idea, we only keep it for backwards compatibility
numberOfElectrons = fRandom->Poisson(energy * REST_Units::eV / fWValue);
}

if (wValue != fWValue) {
// reduce the number of electrons to improve speed
numberOfElectrons = static_cast<unsigned int>(numberOfElectrons * fWValue / wValue);
}

if (numberOfElectrons <= 0) {
Expand All @@ -202,14 +220,12 @@ TRestEvent* TRestDetectorElectronDiffusionProcess::ProcessEvent(TRestEvent* inpu

const Double_t energyPerElectron = energy * REST_Units::eV / numberOfElectrons;

while (numberOfElectrons > 0) {
numberOfElectrons--;

Double_t longitudinalDiffusion =
10. * TMath::Sqrt(driftDistance / 10.) * fLongitudinalDiffusionCoefficient; // mm
Double_t transversalDiffusion =
10. * TMath::Sqrt(driftDistance / 10.) * fTransversalDiffusionCoefficient; // mm
Double_t longitudinalDiffusion =
10. * TMath::Sqrt(driftDistance / 10.) * fLongitudinalDiffusionCoefficient; // mm
Double_t transversalDiffusion =
10. * TMath::Sqrt(driftDistance / 10.) * fTransversalDiffusionCoefficient; // mm

for (unsigned int i = 0; i < numberOfElectrons; i++) {
if (fAttachment > 0) {
// TODO: where is this formula from?
isAttached = (fRandom->Uniform(0, 1) > pow(1 - fAttachment, driftDistance / 10.));
Expand Down Expand Up @@ -240,7 +256,7 @@ TRestEvent* TRestDetectorElectronDiffusionProcess::ProcessEvent(TRestEvent* inpu
1E-6 * plane->GetNormal().Z()); // add a delta to make sure readout finds it
}

if (!fCheckIsInside && !plane->IsInside(positionAfterDiffusion)) {
if (fCheckIsInside && !plane->IsInside(positionAfterDiffusion)) {
// electron has been moved outside the readout plane
continue;
}
Expand Down Expand Up @@ -280,13 +296,14 @@ void TRestDetectorElectronDiffusionProcess::InitFromConfigFile() {
fGasPressure = GetDblParameterWithUnits("gasPressure", -1.);
fElectricField = GetDblParameterWithUnits("electricField", -1.);
fWValue = GetDblParameterWithUnits("WValue", 0.0) * REST_Units::eV;
fFanoFactor = GetDblParameterWithUnits("fanoFactor", 0.0);
fAttachment = StringToDouble(GetParameter("attachment", "0"));
fLongitudinalDiffusionCoefficient =
StringToDouble(GetParameter("longitudinalDiffusionCoefficient", "-1"));
if (fLongitudinalDiffusionCoefficient == -1)
fLongitudinalDiffusionCoefficient = StringToDouble(GetParameter("longDiff", "-1"));
else {
RESTWarning << "longitudinalDiffusionCoefficient is now OBSOLETE! It will soon dissapear."
RESTWarning << "longitudinalDiffusionCoefficient is now OBSOLETE! It will soon disappear."
<< RESTendl;
RESTWarning << " Please use the shorter form of this parameter : longDiff" << RESTendl;
}
Expand All @@ -295,12 +312,13 @@ void TRestDetectorElectronDiffusionProcess::InitFromConfigFile() {
if (fTransversalDiffusionCoefficient == -1)
fTransversalDiffusionCoefficient = StringToDouble(GetParameter("transDiff", "-1"));
else {
RESTWarning << "transversalDiffusionCoefficient is now OBSOLETE! It will soon dissapear." << RESTendl;
RESTWarning << "transversalDiffusionCoefficient is now OBSOLETE! It will soon disappear." << RESTendl;
RESTWarning << " Please use the shorter form of this parameter : transDiff" << RESTendl;
}
fMaxHits = StringToInteger(GetParameter("maxHits", "1000"));
fSeed = StringToDouble(GetParameter("seed", "0"));
fPoissonElectronExcitation = StringToBool(GetParameter("poissonElectronExcitation", "false"));
fSeed = static_cast<UInt_t>(StringToInteger(GetParameter("seed", "0")));
fPoissonElectronExcitation = StringToBool(GetParameter("poissonElectronExcitation", "true"));
fUnitElectronEnergy = StringToBool(GetParameter("unitElectronEnergy", "false"));
fCheckIsInside = StringToBool(GetParameter("checkIsInside", "true"));
fCheckIsInside = StringToBool(GetParameter("checkIsInside", "false"));
fUseFanoFactor = StringToBool(GetParameter("useFano", "false"));
}

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