MultipleScatteringUpdator.cc

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#include "TrackingTools/MaterialEffects/interface/MultipleScatteringUpdator.h"
#include "DataFormats/GeometrySurface/interface/MediumProperties.h"

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

void oldMUcompute(const TrajectoryStateOnSurface& TSoS, const PropagationDirection propDir, double mass, double ptmin);

//#define DBG_MSU

//
// Computation of contribution of multiple scatterning to covariance matrix
//   of local parameters based on Highland formula for sigma(alpha) in plane.
//
void MultipleScatteringUpdator::compute(const TrajectoryStateOnSurface& TSoS,
                                        const PropagationDirection propDir,
                                        Effect& effect) const {
  //
  // Get surface
  //
  const Surface& surface = TSoS.surface();
  //
  //
  // Now get information on medium
  //
  const MediumProperties& mp = surface.mediumProperties();
  if UNLIKELY (mp.radLen() == 0)
    return;

  // Momentum vector
  LocalVector d = TSoS.localMomentum();
  float p2 = d.mag2();
  d *= 1.f / sqrt(p2);
  float xf = 1.f / std::abs(d.z());  // increase of path due to angle of incidence
  // calculate general physics things
  constexpr float amscon = 1.8496e-4;  // (13.6MeV)**2
  const float m2 = mass() * mass();    // use mass hypothesis from constructor
  float e2 = p2 + m2;
  float beta2 = p2 / e2;
  // calculate the multiple scattering angle
  float radLen = mp.radLen() * xf;  // effective rad. length
  float sigt2 = 0.;                 // sigma(alpha)**2

  // Calculated rms scattering angle squared.
  float fact = 1.f + 0.038f * unsafe_logf<2>(radLen);
  fact *= fact;
  float a = fact / (beta2 * p2);
  sigt2 = amscon * radLen * a;

  if (thePtMin > 0) {
#ifdef DBG_MSU
    std::cout << "Original rms scattering = " << sqrt(sigt2);
#endif
    // Inflate estimated rms scattering angle, to take into account
    // that 1/p is not known precisely.
    AlgebraicSymMatrix55 const& covMatrix = TSoS.localError().matrix();
    float error2_QoverP = covMatrix(0, 0);
    // Formula valid for ultra-relativistic particles.
    //      sigt2 *= (1. + p2 * error2_QoverP);
    // Exact formula
    sigt2 *= 1.f + error2_QoverP * (p2 + m2 * beta2 * (5.f + 3.f * p2 * error2_QoverP));
#ifdef DBG_MSU
    std::cout << " new = " << sqrt(sigt2);
#endif
    // Convert Pt constraint to P constraint, neglecting uncertainty in
    // track angle.
    float pMin2 = thePtMin * thePtMin * (p2 / TSoS.globalMomentum().perp2());
    // Use P constraint to calculate rms maximum scattering angle.
    float betaMin2 = pMin2 / (pMin2 + m2);
    float a_max = fact / (betaMin2 * pMin2);
    float sigt2_max = amscon * radLen * a_max;
    if (sigt2 > sigt2_max)
      sigt2 = sigt2_max;
#ifdef DBG_MSU
    std::cout << " after P constraint (" << pMin << ") = " << sqrt(sigt2);
    std::cout << " for track with 1/p=" << 1 / p << "+-" << sqrt(error2_QoverP) << std::endl;
#endif
  }

  float isl2 = 1.f / d.perp2();
  float cl2 = (d.z() * d.z());
  float cf2 = (d.x() * d.x()) * isl2;
  float sf2 = (d.y() * d.y()) * isl2;
  // Create update (transformation of independant variations
  //   on angle in orthogonal planes to local parameters.
  float den = 1.f / (cl2 * cl2);
  using namespace materialEffect;
  effect.deltaCov[msxx] += (den * sigt2) * (sf2 * cl2 + cf2);
  effect.deltaCov[msxy] += (den * sigt2) * (d.x() * d.y());
  effect.deltaCov[msyy] += (den * sigt2) * (cf2 * cl2 + sf2);

  /*
    std::cout << "new " <<  theDeltaCov(1,1) << " " <<  theDeltaCov(1,2)  << " " <<  theDeltaCov(2,2) << std::endl;
    oldMUcompute(TSoS,propDir, mass(), thePtMin);
  */
}

//
// Computation of contribution of multiple scatterning to covariance matrix
//   of local parameters based on Highland formula for sigma(alpha) in plane.
//
void oldMUcompute(const TrajectoryStateOnSurface& TSoS, const PropagationDirection propDir, float mass, float thePtMin) {
  //
  // Get surface
  //
  const Surface& surface = TSoS.surface();
  //
  //
  // Now get information on medium
  //
  if (surface.mediumProperties().isValid()) {
    // Momentum vector
    LocalVector d = TSoS.localMomentum();
    float p = d.mag();
    d *= 1. / p;
    // MediumProperties mp(0.02, .5e-4);
    const MediumProperties& mp = surface.mediumProperties();
    float xf = 1. / fabs(d.z());  // increase of path due to angle of incidence
    // calculate general physics things
    const float amscon = 1.8496e-4;  // (13.6MeV)**2
    const float m = mass;            // use mass hypothesis from constructor
    float e = sqrt(p * p + m * m);
    float beta = p / e;
    // calculate the multiple scattering angle
    float radLen = mp.radLen() * xf;  // effective rad. length
    float sigt2 = 0.;                 // sigma(alpha)**2
    if (radLen > 0) {
      // Calculated rms scattering angle squared.
      float a = (1. + 0.038 * log(radLen)) / (beta * p);
      a *= a;
      sigt2 = amscon * radLen * a;
      if (thePtMin > 0) {
#ifdef DBG_MSU
        std::cout << "Original rms scattering = " << sqrt(sigt2);
#endif
        // Inflate estimated rms scattering angle, to take into account
        // that 1/p is not known precisely.
        AlgebraicSymMatrix55 covMatrix = TSoS.localError().matrix();
        float error2_QoverP = covMatrix(0, 0);
        // Formula valid for ultra-relativistic particles.
        //      sigt2 *= (1. + (p*p) * error2_QoverP);
        // Exact formula
        sigt2 *= (1. + (p * p) * error2_QoverP * (1. + 5 * m * m / (e * e) + 3 * m * m * beta * beta * error2_QoverP));
#ifdef DBG_MSU
        std::cout << " new = " << sqrt(sigt2);
#endif
        // Convert Pt constraint to P constraint, neglecting uncertainty in
        // track angle.
        float pMin = thePtMin * (TSoS.globalMomentum().mag() / TSoS.globalMomentum().perp());
        // Use P constraint to calculate rms maximum scattering angle.
        float betaMin = pMin / sqrt(pMin * pMin + m * m);
        float a_max = (1. + 0.038 * log(radLen)) / (betaMin * pMin);
        a_max *= a_max;
        float sigt2_max = amscon * radLen * a_max;
        if (sigt2 > sigt2_max)
          sigt2 = sigt2_max;
#ifdef DBG_MSU
        std::cout << " after P constraint (" << pMin << ") = " << sqrt(sigt2);
        std::cout << " for track with 1/p=" << 1 / p << "+-" << sqrt(error2_QoverP) << std::endl;
#endif
      }
    }
    float sl = d.perp();
    float cl = d.z();
    float cf = d.x() / sl;
    float sf = d.y() / sl;
    // Create update (transformation of independant variations
    //   on angle in orthogonal planes to local parameters.
    std::cout << "old " << sigt2 * (sf * sf * cl * cl + cf * cf) / (cl * cl * cl * cl) << " "
              << sigt2 * (cf * sf * sl * sl) / (cl * cl * cl * cl) << " "
              << sigt2 * (cf * cf * cl * cl + sf * sf) / (cl * cl * cl * cl) << std::endl;
  }
}