RealisticCaloDigiScinPpd.cc

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// Calorimeter digitiser for the IDC ECAL and HCAL
// For other detectors/models SimpleCaloDigi should be used

#include "RealisticCaloDigiScinPpd.h"

#include <marlin/Global.h>

#include <iostream>
#include <string>
#include <algorithm>
#include <assert.h>

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

using namespace std;
//using namespace lcio ;
using namespace marlin ;

RealisticCaloDigiScinPpd aRealisticCaloDigiScinPpd ;

RealisticCaloDigiScinPpd::RealisticCaloDigiScinPpd() : RealisticCaloDigi::Processor("RealisticCaloDigiScinPpd") {

  _description = "Performs digitization of sim calo hits..." ;


  registerProcessorParameter("ppd_mipPe" ,
                             "# Photo-electrons per MIP (scintillator): used to poisson smear #PEs if >0" ,
                             _PPD_pe_per_mip,
                             (float)10.);

  registerProcessorParameter("ppd_npix" ,
                             "total number of MPPC/SiPM pixels for implementation of saturation effect" ,
                             _PPD_n_pixels,
                             (int)10000);

  registerProcessorParameter("ppd_npix_uncert" ,
                             "fractional uncertainty of effective total number of MPPC/SiPM pixels" ,
                             _misCalibNpix,
                             float (0.05) );

  registerProcessorParameter("ppd_pix_spread",
                             "variation of PPD pixel signal (as a fraction: 0.01=1%)",
                             _pixSpread,
                             float (0.05));

}


float RealisticCaloDigiScinPpd::convertEnergy( float energy, int inUnit ) const { // convert energy from input to output scale (NPE)
  if      ( inUnit==NPE ) return energy;
  else if ( inUnit==MIP ) return _PPD_pe_per_mip*energy;
  else if ( inUnit==GEVDEP ) return _PPD_pe_per_mip*energy/_calib_mip;
  else streamlog_out (ERROR) << "unknown unit " << inUnit << std::endl;
  assert (0);
}

float RealisticCaloDigiScinPpd::digitiseDetectorEnergy(float energy) const {
  // input energy in deposited GeV
  // output in npe
  float npe = energy*_PPD_pe_per_mip/_calib_mip; // convert to pe scale

  if (_PPD_n_pixels>0){
    // apply average sipm saturation behaviour
    npe = _PPD_n_pixels*(1.0 - exp( -npe/_PPD_n_pixels ) );
    //apply binomial smearing
    float p = npe/_PPD_n_pixels; // fraction of hit pixels on SiPM
    npe = CLHEP::RandBinomial::shoot(_PPD_n_pixels, p); //npe now quantised to integer pixels

    if (_pixSpread>0) {
      // variations in pixel capacitance
      npe *= CLHEP::RandGauss::shoot(1, _pixSpread/sqrt(npe) );
    }
  }

  return npe;
}