TrackingTools/MaterialEffects/src/EnergyLossUpdator.cc - master - githubmirror/cmssw

TrackingTools/MaterialEffects/src/EnergyLossUpdator.cc
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31 май 2019, 13:16
31 май 2019, 13:1614da925
#include "TrackingTools/MaterialEffects/interface/EnergyLossUpdator.h"
#include "DataFormats/GeometrySurface/interface/MediumProperties.h"

#include "DataFormats/Math/interface/approx_exp.h"
#include "DataFormats/Math/interface/approx_log.h"

void oldComputeBetheBloch(const LocalVector& localP, const MediumProperties& materialConstants, double mass);
void oldComputeElectrons(const LocalVector& localP,
                         const MediumProperties& materialConstants,
                         const PropagationDirection propDir);

//
// Computation of contribution of energy loss to momentum and covariance
// matrix of local parameters based on Bethe-Bloch. For electrons
// contribution of radiation acc. to Bethe & Heitler.
//
void EnergyLossUpdator::compute(const TrajectoryStateOnSurface& TSoS,
                                const PropagationDirection propDir,
                                Effect& effect) const {
  //
  // Get surface
  //
  const Surface& surface = TSoS.surface();
  //
  //
  // Now get information on medium
  //
  if (surface.mediumProperties().isValid()) {
    //
    // Bethe-Bloch
    //
    if (mass() > 0.001)
      computeBetheBloch(TSoS.localMomentum(), surface.mediumProperties(), effect);
    //
    // Special treatment for electrons (currently rather crude
    // distinction using mass)
    //
    else
      computeElectrons(TSoS.localMomentum(), surface.mediumProperties(), propDir, effect);
    if (propDir != alongMomentum)
      effect.deltaP *= -1.;
  }
}
//
// Computation of energy loss according to Bethe-Bloch
//
void EnergyLossUpdator::computeBetheBloch(const LocalVector& localP,
                                          const MediumProperties& materialConstants,
                                          Effect& effect) const {
  //
  // calculate absolute momentum and correction to path length from angle
  // of incidence
  //

  typedef float Float;

  Float p2 = localP.mag2();
  Float xf = std::abs(std::sqrt(p2) / localP.z());

  // constants
  const Float m2 = mass() * mass();  // use mass hypothesis from constructor

  constexpr Float emass = 0.511e-3;
  constexpr Float poti = 16.e-9 * 10.75;                 // = 16 eV * Z**0.9, for Si Z=14
  const Float eplasma = 28.816e-9 * sqrt(2.33 * 0.498);  // 28.816 eV * sqrt(rho*(Z/A)) for Si
  const Float delta0 = 2 * log(eplasma / poti) - 1.;

  // calculate general physics things
  Float im2 = Float(1.) / m2;
  Float e2 = p2 + m2;
  Float e = std::sqrt(e2);
  Float beta2 = p2 / e2;
  Float eta2 = p2 * im2;
  Float ratio2 = (emass * emass) * im2;
  Float emax = Float(2.) * emass * eta2 / (Float(1.) + Float(2.) * emass * e * im2 + ratio2);

  Float xi = materialConstants.xi() * xf;
  xi /= beta2;

  Float dEdx = xi * (unsafe_logf<2>(Float(2.) * emass * emax / (poti * poti)) - Float(2.) * (beta2)-delta0);

  Float dEdx2 = xi * emax * (Float(1.) - Float(0.5) * beta2);
  Float dP = dEdx / std::sqrt(beta2);
  Float sigp2 = dEdx2 / (beta2 * p2 * p2);
  effect.deltaP += -dP;
  using namespace materialEffect;
  effect.deltaCov[elos] += sigp2;

  // std::cout << "pion new " <<  theDeltaP << " " << theDeltaCov(0,0) << std::endl;
  // oldComputeBetheBloch (localP, materialConstants, mass());
}
//
// Computation of energy loss for electrons
//
void EnergyLossUpdator::computeElectrons(const LocalVector& localP,
                                         const MediumProperties& materialConstants,
                                         const PropagationDirection propDir,
                                         Effect& effect) const {
  //
  // calculate absolute momentum and correction to path length from angle
  // of incidence
  //
  float p2 = localP.mag2();
  float p = std::sqrt(p2);
  float normalisedPath = std::abs(p / localP.z()) * materialConstants.radLen();
  //
  // Energy loss and variance according to Bethe and Heitler, see also
  // Comp. Phys. Comm. 79 (1994) 157.
  //
  const float l3ol2 = std::log(3.) / std::log(2.);
  float z = unsafe_expf<3>(-normalisedPath);
  float varz = unsafe_expf<3>(-normalisedPath * l3ol2) - z * z;
  // exp(-2*normalisedPath);

  if (propDir == oppositeToMomentum) {
    //
    // for backward propagation: delta(1/p) is linear in z=p_outside/p_inside
    // convert to obtain equivalent delta(p). Sign of deltaP is corrected
    // in method compute -> deltaP<0 at this place!!!
    //
    effect.deltaP += -p * (1.f / z - 1.f);
    using namespace materialEffect;
    effect.deltaCov[elos] += varz / p2;
  } else {
    //
    // for forward propagation: calculate in p (linear in 1/z=p_inside/p_outside),
    // then convert sig(p) to sig(1/p).
    //
    effect.deltaP += p * (z - 1.f);
    //    float f = 1/p/z/z;
    // patch to ensure consistency between for- and backward propagation
    float f2 = 1.f / (p2 * z * z);
    using namespace materialEffect;
    effect.deltaCov[elos] += f2 * varz;
  }

  // std::cout << "electron new " <<  theDeltaP << " " << theDeltaCov(0,0) << std::endl;
  // oldComputeElectrons (localP, materialConstants, propDir);
}

///

void oldComputeBetheBloch(const LocalVector& localP, const MediumProperties& materialConstants, double mass) {
  double theDeltaP = 0., theDeltaCov = 0;

  //
  // calculate absolute momentum and correction to path length from angle
  // of incidence
  //
  double p = localP.mag();
  double xf = fabs(p / localP.z());
  // constants
  const double m = mass;  // use mass hypothesis from constructor

  const double emass = 0.511e-3;
  const double poti = 16.e-9 * 10.75;                     // = 16 eV * Z**0.9, for Si Z=14
  const double eplasma = 28.816e-9 * sqrt(2.33 * 0.498);  // 28.816 eV * sqrt(rho*(Z/A)) for Si
  const double delta0 = 2 * log(eplasma / poti) - 1.;

  // calculate general physics things
  double e = sqrt(p * p + m * m);
  double beta = p / e;
  double gamma = e / m;
  double eta2 = beta * gamma;
  eta2 *= eta2;
  //  double lnEta2 = log(eta2);
  double ratio = emass / m;
  double emax = 2. * emass * eta2 / (1. + 2. * ratio * gamma + ratio * ratio);
  // double delta = delta0 + lnEta2;

  // calculate the mean and sigma of energy loss
  // xi = d[g/cm2] * 0.307075MeV/(g/cm2) * Z/A * 1/2
  double xi = materialConstants.xi() * xf;
  xi /= (beta * beta);

  //   double dEdx = xi*(log(2.*emass*eta2*emax/(poti*poti)) - 2.*(beta*beta));
  //double dEdx = xi*(log(2.*emass*emax/(poti*poti))+lnEta2 - 2.*(beta*beta) - delta);

  double dEdx = xi * (log(2. * emass * emax / (poti * poti)) - 2. * (beta * beta) - delta0);
  double dEdx2 = xi * emax * (1. - 0.5 * (beta * beta));
  double dP = dEdx / beta;
  double sigp2 = dEdx2 * e * e / (p * p * p * p * p * p);
  theDeltaP += -dP;
  theDeltaCov += sigp2;

  std::cout << "pion old " << theDeltaP << " " << theDeltaCov << std::endl;
}

void oldComputeElectrons(const LocalVector& localP,
                         const MediumProperties& materialConstants,
                         const PropagationDirection propDir) {
  double theDeltaP = 0., theDeltaCov = 0;

  //
  // calculate absolute momentum and correction to path length from angle
  // of incidence
  //
  double p = localP.mag();
  double normalisedPath = fabs(p / localP.z()) * materialConstants.radLen();
  //
  // Energy loss and variance according to Bethe and Heitler, see also
  // Comp. Phys. Comm. 79 (1994) 157.
  //
  double z = exp(-normalisedPath);
  double varz = exp(-normalisedPath * log(3.) / log(2.)) - z * z;
  // exp(-2*normalisedPath);

  if (propDir == oppositeToMomentum) {
    //
    // for backward propagation: delta(1/p) is linear in z=p_outside/p_inside
    // convert to obtain equivalent delta(p). Sign of deltaP is corrected
    // in method compute -> deltaP<0 at this place!!!
    //
    theDeltaP += -p * (1 / z - 1);
    theDeltaCov += varz / (p * p);
  } else {
    //
    // for forward propagation: calculate in p (linear in 1/z=p_inside/p_outside),
    // then convert sig(p) to sig(1/p).
    //
    theDeltaP += p * (z - 1);
    //    double f = 1/p/z/z;
    // patch to ensure consistency between for- and backward propagation
    double f = 1. / (p * z);
    theDeltaCov += f * f * varz;
  }

  std::cout << "electron old " << theDeltaP << " " << theDeltaCov << std::endl;
}