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ElectronSmearer.cxx

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// ElectronSmearer.cxx
//
// Implementation of the Electron Smearer class
//
// Only the smear() method is overridden
//
//
// Authors: H.T. Phillips, P.Clarke, E.Richter-Was, P.Sherwood, R.Steward
//
//
#include "AtlfastAlgs/ElectronSmearer.h"

#include <cmath>

#include "CLHEP/Vector/LorentzVector.h"


#include "CLHEP/Random/JamesRandom.h"
#include "CLHEP/Random/RandGauss.h"

namespace Atlfast {

  HepLorentzVector ElectronSmearer::smear (const HepLorentzVector& avec) {
    // do the smearing, copied verbatim (except for ROOT dependencies)
    // from electronmaker codein Atlfast++
    //
    // This code has not otherwise been altered which is why it is all very
    // procedural
    //
    // Parametrisation was by L.Poggioli

    double rpilup = 0.0;
    double aa, bb, sigph1, sigph, sigpu;
    double sqrtene = sqrt(avec.e());
    double abseta  = fabs(avec.pseudoRapidity());

    while (1) {
      aa=randGauss()->fire();
      //bb=randGauss()->fire();
      sigph1 = aa*0.12/sqrtene;
      if (1.0 + sigph1 <= 0.0) continue;
      sigph = sigph1;
      if (abseta < 1.4) {
        while (1) {
          aa=randGauss()->fire();
          bb=randGauss()->fire();
          sigph1 = aa*0.245/avec.perp() + bb*0.007;
          if (1.0+sigph1 > 0) break;
        }
      } else {
        while (1) {
          aa=randGauss()->fire();
          bb=randGauss()->fire();
          sigph1 = aa*0.306*((2.4-abseta)+0.228)/avec.e() + bb*0.007;
          if (1.0+sigph1 > 0) break;
        }
      }
      sigph += sigph1;
      if (m_lumi == 2) {
        if (abseta < 0.6) rpilup = 0.32;
        if (abseta > 0.6 && abseta < 1.4) rpilup = 0.295;
        if (abseta > 1.4) rpilup = 0.27;
        while (1) {
          aa=randGauss()->fire();
          //bb=randGauss()->fire();
          sigpu = aa*rpilup/avec.perp();
          if (1.0+sigpu > 0) break;
        }
        sigph += sigpu;
      }
      if (1.0 + sigph > 0) break;
    }

    //now sigph is the electron "sigma" and we do the following a la Atlfast++ electron maker:
    HepLorentzVector bvec(avec.px()*(1.0+sigph), avec.py()*(1.0+sigph), avec.pz()*(1.0+sigph), avec.e() *(1.0+sigph));

    return bvec;
  }

} // end of namespace bracket

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