SiLinearChargeCollectionDrifter.cc

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#include "SiLinearChargeCollectionDrifter.h"
#include "vdt/log.h"

SiLinearChargeCollectionDrifter::SiLinearChargeCollectionDrifter(double dc, double cdr, double dv, double av)
    :  // Everything which does not depend on the specific det
      diffusionConstant(dc),
      chargeDistributionRMS(cdr),
      depletionVoltage(dv),
      appliedVoltage(av) {}

SiChargeCollectionDrifter::collection_type SiLinearChargeCollectionDrifter::drift(
    const SiChargeCollectionDrifter::ionization_type& ion, const LocalVector& driftDir, double mt, double tn) {
  // prepare output
  collection_type _temp;
  _temp.resize(ion.size());
  // call the drift method for each deposit
  for (size_t i = 0; i < ion.size(); i++) {
    _temp[i] = drift(ion[i], driftDir, mt, tn);
  }
  return _temp;
}

SignalPoint SiLinearChargeCollectionDrifter::drift(const EnergyDepositUnit& edu,
                                                   const LocalVector& drift,
                                                   double moduleThickness,
                                                   double timeNormalisation) {
  // computes the fraction of the module the charge has to drift through,
  // ensuring it is bounded in [0,1]
  double depth = (moduleThickness / 2. - edu.z());
  double thicknessFraction = depth / moduleThickness;
  thicknessFraction = thicknessFraction > 0. ? thicknessFraction : 0.;
  thicknessFraction = thicknessFraction < 1. ? thicknessFraction : 1.;

  // computes the drift time in the sensor
  double driftTime = -timeNormalisation * vdt::fast_log(1. - 2 * depletionVoltage * thicknessFraction /
                                                                 (depletionVoltage + appliedVoltage)) +
                     chargeDistributionRMS;

  // returns the signal: an energy on the surface, with a size due to diffusion.
  return SignalPoint(edu.x() + depth * drift.x() / drift.z(),
                     edu.y() + depth * drift.y() / drift.z(),
                     sqrt(2. * diffusionConstant * driftTime),
                     edu.energy());
}