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[MCH] improve track extrapolation to vtx wo MCS correction #14189

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Merged
pillot merged 1 commit into from
Apr 17, 2025
Merged

[MCH] improve track extrapolation to vtx wo MCS correction #14189

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16 changes: 11 additions & 5 deletions Detectors/MUON/MCH/Tracking/include/MCHTracking/TrackExtrap.h
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@
#define O2_MCH_TRACKEXTRAP_H_

#include <cstddef>
#include <optional>

#include <TMatrixD.h>

Expand Down Expand Up @@ -70,17 +71,21 @@ class TrackExtrap
/// Add branson correction resolution to parameter covariances
return extrapToVertex(trackParam, xVtx, yVtx, zVtx, errXVtx, errYVtx, true, false);
}
static bool extrapToVertexWithoutBranson(TrackParam& trackParam, double zVtx)
static bool extrapToVertexWithoutBranson(TrackParam& trackParam, double zVtx,
double xUpstream = 0., double yUpstream = 0.,
std::optional<double> zUpstream = std::nullopt)
{
/// Extrapolate track parameters to vertex, corrected for energy loss effects only
/// Add dispersion due to multiple scattering and energy loss fluctuation to parameter covariances
return extrapToVertex(trackParam, 0., 0., zVtx, 0., 0., false, true);
return extrapToVertex(trackParam, 0., 0., zVtx, 0., 0., false, true, xUpstream, yUpstream, zUpstream);
}
static bool extrapToVertexUncorrected(TrackParam& trackParam, double zVtx)
static bool extrapToVertexUncorrected(TrackParam& trackParam, double zVtx,
double xUpstream = 0., double yUpstream = 0.,
std::optional<double> zUpstream = std::nullopt)
{
/// Extrapolate track parameters to vertex without multiple scattering and energy loss corrections
/// Add dispersion due to multiple scattering to parameter covariances
return extrapToVertex(trackParam, 0., 0., zVtx, 0., 0., false, false);
return extrapToVertex(trackParam, 0., 0., zVtx, 0., 0., false, false, xUpstream, yUpstream, zUpstream);
}

static bool extrapToMID(TrackParam& trackParam);
Expand All @@ -92,7 +97,8 @@ class TrackExtrap

private:
static bool extrapToVertex(TrackParam& trackParam, double xVtx, double yVtx, double zVtx,
double errXVtx, double errYVtx, bool correctForMCS, bool correctForEnergyLoss);
double errXVtx, double errYVtx, bool correctForMCS, bool correctForEnergyLoss,
double xUpstream = 0., double yUpstream = 0., std::optional<double> zUpstream = std::nullopt);

static bool getAbsorberCorrectionParam(double trackXYZIn[3], double trackXYZOut[3], double pTotal,
double& pathLength, double& f0, double& f1, double& f2,
Expand Down
21 changes: 20 additions & 1 deletion Detectors/MUON/MCH/Tracking/src/TrackExtrap.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -276,7 +276,8 @@ bool TrackExtrap::extrapToMID(TrackParam& trackParam)

//__________________________________________________________________________
bool TrackExtrap::extrapToVertex(TrackParam& trackParam, double xVtx, double yVtx, double zVtx,
double errXVtx, double errYVtx, bool correctForMCS, bool correctForEnergyLoss)
double errXVtx, double errYVtx, bool correctForMCS, bool correctForEnergyLoss,
double xUpstream, double yUpstream, std::optional<double> zUpstream)
{
/// Main method for extrapolation to the vertex:
/// Returns the track parameters and covariances resulting from the extrapolation of the current trackParam
Expand All @@ -285,6 +286,8 @@ bool TrackExtrap::extrapToVertex(TrackParam& trackParam, double xVtx, double yVt
/// if correctForMCS=false: add parameter dispersion due to MCS in parameter covariances
/// if correctForEnergyLoss=true: correct parameters for energy loss and add energy loss fluctuation to covariances
/// if correctForEnergyLoss=false: do nothing about energy loss
/// In case correctForMCS=false and the position of the track upstream the absorber is provided, it is used
/// to compute the absorber correction parameters, instead of the extrapolated track position from downstream

if (trackParam.getZ() == zVtx) {
return true; // nothing to be done if already at vertex
Expand All @@ -301,6 +304,18 @@ bool TrackExtrap::extrapToVertex(TrackParam& trackParam, double xVtx, double yVt
}
}

// check the upstream track position with respect to the absorber if provided and used (spectro z<0)
// zUpstream must be >= SAbsZBeg with 100 µm tolerance to account for numerical precision
if (!correctForMCS && zUpstream && *zUpstream < SAbsZBeg - 0.01) {
if (*zUpstream < SAbsZEnd) {
LOG(warning) << "Upstream Z (" << *zUpstream << ") downstream the front absorber (zAbsorberEnd = " << SAbsZEnd << ")";
return false;
} else {
LOG(warning) << "Upstream Z (" << *zUpstream << ") inside the front absorber (" << SAbsZBeg << ", " << SAbsZEnd << ")";
return false;
}
}

// Check the track position with respect to the vertex and the absorber (spectro z<0)
if (trackParam.getZ() > SAbsZEnd) {
if (trackParam.getZ() > zVtx) {
Expand Down Expand Up @@ -328,6 +343,10 @@ bool TrackExtrap::extrapToVertex(TrackParam& trackParam, double xVtx, double yVt
trackXYZIn[2] = SAbsZBeg;
trackXYZIn[0] = trackXYZOut[0] + (xVtx - trackXYZOut[0]) / (zVtx - trackXYZOut[2]) * (trackXYZIn[2] - trackXYZOut[2]);
trackXYZIn[1] = trackXYZOut[1] + (yVtx - trackXYZOut[1]) / (zVtx - trackXYZOut[2]) * (trackXYZIn[2] - trackXYZOut[2]);
} else if (zUpstream) { // or linear propagation to the upstream track position
trackXYZIn[2] = SAbsZBeg;
trackXYZIn[0] = trackXYZOut[0] + (xUpstream - trackXYZOut[0]) / (*zUpstream - trackXYZOut[2]) * (trackXYZIn[2] - trackXYZOut[2]);
trackXYZIn[1] = trackXYZOut[1] + (yUpstream - trackXYZOut[1]) / (*zUpstream - trackXYZOut[2]) * (trackXYZIn[2] - trackXYZOut[2]);
} else { // or standard propagation without vertex constraint
TrackParam trackParamIn(trackParam);
if (!extrapToZ(trackParamIn, SAbsZBeg)) {
Expand Down