CSCGasCollisions.cc

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// This implements the CSC gas ionization simulation.
// It requires the GEANT3-generated tables in the input file 
// (default) MuonData/EndcapData/collisions.dat

// Outstanding problems to fix 15-Oct-2003
// - ework must be re-tuned once eion or ework are removed before delta e range estimation.
// - logic of long-range delta e's must be revisited.
// - The code here needs to have diagnostic output removed, or reduced. PARTICULARLY filling of std::vectors!
// - 'gap' is a misnomer, when simhit entry and exit don't coincide with gap edges
//  so the CSCCrossGap might better be named as a simhit-related thing. 
// 22-Jan-2004 Corrected position of trap for 'infinite' loop while
//    generating steps. Output files (debugV-flagged only) require SC flag.
//    Increase deCut from 10 keV to 100 keV to accomodate protons!

#include "FWCore/Utilities/interface/Exception.h"
#include "DataFormats/GeometryVector/interface/LocalVector.h"
#include "SimMuon/CSCDigitizer/src/CSCGasCollisions.h"
#include "Utilities/General/interface/FileInPath.h"
#include "FWCore/MessageLogger/interface/MessageLogger.h"
#include <iostream>
#include <fstream>
#include <cassert>

// stdlib math functions
// for 'abs':
#include <cstdlib>
// for usual math functions:
#include <cmath>

// stdlib container trickery
// for 'for_each':
#include <algorithm>
// for 'greater' and 'less':
#include <functional>
// for 'accumulate':
#include <numeric>
#include <iterator>

using namespace std;
/* Gas mixture is Ar/CO2/CF4 = 40/50/10
We'll use the ioinzation energies
Ar    15.8 eV
CO2   13.7 eV
CF4    17.8
to arrive at a weighted average of 14.95 */

CSCGasCollisions::CSCGasCollisions() : me("CSCGasCollisions"),
  gasDensity( 2.1416e-03 ), 
  deCut( 1.e05 ), eion( 14.95 ), ework( 34.0 ), clusterExtent( 0.001 ),
  theGammaBins(N_GAMMA, 0.), theEnergyBins(N_ENERGY, 0.), 
  theCollisionTable(N_ENTRIES, 0.), theCrossGap( 0 ),
  theParticleDataTable(0),
  theRandFlat(0),
  theRandExponential(0),
  saveGasCollisions ( false )
{

  edm::LogInfo(me) << "Constructing a " << me << ":"; 
  edm::LogInfo(me) << "gas density = " << gasDensity << " g/cm3";
  edm::LogInfo(me) << "max eloss per collision allowed = " << deCut/1000. 
       << " keV (for higher elosses, hits should have been simulated.)";
  edm::LogInfo(me) << "ionization threshold = " << eion << " eV";
  edm::LogInfo(me) << "effective work function = " << ework << " eV";
  edm::LogInfo(me) << "cluster extent = " << clusterExtent*1.e04 << " micrometres";
  edm::LogInfo(me) << "Save gas collision info to files when using debugV? " << saveGasCollisions;

  readCollisionTable();
}

CSCGasCollisions::~CSCGasCollisions() {
  edm::LogInfo(me) << "Destructing a " << me;
  delete theCrossGap;
  delete theRandFlat;
  delete theRandExponential;
}

void CSCGasCollisions::readCollisionTable() {

  // I'd prefer to allow comments in the data file which means
  // complications of reading line-by-line and then item-by-item.

  // Is float OK? Or do I need double?

  // Do I need any sort of error trapping?

  // We use the default CMSSW data file path
  // We use the default file name 'collisions.dat'
   
  // This can be reset in .orcarc by SimpleConfigurable
  //    Muon:Endcap:CollisionsFile

  string path( getenv( "CMSSW_SEARCH_PATH" ) );
  // TODO make configurable
  string colliFile = "SimMuon/CSCDigitizer/data/collisions.dat";
  FileInPath f1( path, colliFile );
  if (f1() == 0 ) {
    string errorMessage = "Input file " + colliFile + "not found";
    edm::LogError("CSCGasCollisions") << errorMessage << " in path " << path
          << "\nSet Muon:Endcap:CollisionsFile in .orcarc to the "
         " location of the file relative to ORCA_DATA_PATH." ;
    throw cms::Exception( " Endcap Muon gas collisions data file not found.");
  }
  else {
    edm::LogInfo(me) << ": reading " << f1.name();
  }

  ifstream & fin = *f1();

  if (fin == 0) {
    string errorMessage = "Cannot open input file " + path + colliFile;
    edm::LogError("CSCGasCollisions") << errorMessage;
    throw cms::Exception(errorMessage);
  }

  fin.clear( );                  // Clear eof read status
  fin.seekg( 0, ios::beg );      // Position at start of file

  // @@ We had better have the right sizes everywhere or all
  // hell will break loose. There's no trapping.
  LogTrace(me) << "Reading gamma bins";
  int j = 0;
  for(int i = 0; i<N_GAMMA; ++i) {
    fin >> theGammaBins[i];
    LogTrace(me) << ++j << "   " << theGammaBins[i];
  }

  j = 0;
  LogTrace(me) << "Reading energy bins \n";
  for(int i = 0; i<N_ENERGY; ++i) {
     fin >> theEnergyBins[i];
     LogTrace(me) << ++j << "   " << theEnergyBins[i];
  }

  j = 0;
  LogTrace(me) << "Reading collisions table \n";

  for(int i = 0; i<N_ENTRIES; ++i) {
     fin >> theCollisionTable[i];
     LogTrace(me) << ++j << "   " << theCollisionTable[i];
  }

  fin.close();
}


void CSCGasCollisions::setParticleDataTable(const ParticleDataTable * pdt)
{
  theParticleDataTable = pdt;
}


void CSCGasCollisions::setRandomEngine(CLHEP::HepRandomEngine & engine)
{
  theRandFlat = new CLHEP::RandFlat(engine);
  theRandExponential = new CLHEP::RandExponential(engine);
}


void CSCGasCollisions::simulate( const PSimHit& simHit, 
  std::vector<LocalPoint>& positions, std::vector<int>& electrons ) {

  const float epsilonL = 0.01;                     // Shortness of simhit 'length'
  //  const float max_gap_z = 1.5;                     // Gas gaps are 0.5 or 1.0 cm

  // Note that what I call the 'gap' may in fact be the 'length' of a PSimHit which
  // does not start and end on the gap edges. This confuses the nomenclature at least.

  double mom    = simHit.pabs();
  int iam       = simHit.particleType();           // PDG type
  delete theCrossGap;                              // before building new one
  assert(theParticleDataTable != 0);
  ParticleData const * particle = theParticleDataTable->particle( simHit.particleType() );
  double mass = 0.105658; // assume a muon
  if(particle == 0)
  {
     edm::LogError("CSCGasCollisions") << "Cannot find particle of type " << simHit.particleType()
                                       << " in the PDT";
  }
  else 
  {
    mass = particle->mass();
  }

  theCrossGap   = new CSCCrossGap( mass, mom, simHit.exitPoint() - simHit.entryPoint() );
  float gapSize = theCrossGap->length();

  // Test the simhit 'length' (beware of angular effects)
  //  if ( gapSize <= epsilonL || gapSize > max_gap_z ) {
  if ( gapSize <= epsilonL ) {
    LogTrace(me) << ": WARNING! simhit entry and exit are very close: \n"
      << "\n entry = " << simHit.entryPoint()
      << "\n exit  = " << simHit.exitPoint()
      << "\n particle type = " << iam << ", momentum = " << mom 
      << ", gap length = " << gapSize;
    return; //@@ Just skip this PSimHit
  }

  // Interpolate the table for current gamma value
  // Extract collisions binned by energy loss values, for this gamma
  std::vector<float> collisions(N_ENERGY);
  double loggam = theCrossGap->logGamma(); 
  fillCollisionsForThisGamma( static_cast<float>(loggam), collisions );

  double anmin = exp(collisions[N_ENERGY-1]);
  double anmax = exp(collisions[0]);
  double amu   = anmax - anmin;

  LogTrace(me) << "collisions extremes = " << collisions[N_ENERGY-1]
     << ", " << collisions[0] << "\n"
     << "anmin = " << anmin << ", anmax = " << anmax << "\n"
     << "amu = " << amu << "\n";

  float dedx       = 0.; // total energy loss
  double sum_steps = 0.; // total distance across gap (along simhit direction)
  int n_steps      = 0;  // no. of steps/primary collisions
  int n_try        = 0;  // no. of tries to generate steps
  double step      = -1.; // Sentinel for start

  LocalPoint layerLocalPoint( simHit.entryPoint() );

  // step/primary collision loop
  while ( sum_steps < gapSize) {
    ++n_try;
    if ( n_try > MAX_STEPS ) {
          LogTrace(me) << ": n_try=" << n_try << " is too large. Skip simhit."
           << "\n particle type=" << iam << ", momentum= " << mom
           << "\n gapSize=" << gapSize << ", last step=" << step 
           << ", sum_steps=" << sum_steps << ", n_steps=" << n_steps;
        break;
    }
    step = generateStep( amu );
    if ( sum_steps + step > gapSize ) break;

    float eloss = generateEnergyLoss( amu, anmin, anmax, collisions );

    // Is the eloss too large? (then GEANT should have produced hits!)
    if ( eloss > deCut ) {
      LogTrace(me) << "eloss > " << deCut << " = " << eloss;
      continue; // to generate another collision/step
    }

    dedx      += eloss; // the energy lost from the ionizing particle
    sum_steps += step;  // the position of the ionizing particle
    ++n_steps;          // the number of primary collisions
    
    if (n_steps > MAX_STEPS ) { // Extra-careful trap for bizarreness
        edm::LogInfo(me) << ": n_steps=" << n_steps << " is too large. Skip simhit.";
        edm::LogInfo(me) << "particle type=" << iam << ", momentum= " << mom;
        edm::LogInfo(me) << "gapSize=" << gapSize << ", last step=" << step 
             << ", sum_steps=" << sum_steps;
        break;
    }
    LogTrace(me) << "sum_steps = " << sum_steps << ", dedx = " << dedx;
    
    // Generate ionization. 
    // eion is the minimum energy at which ionization can occur in the gas
    if ( eloss > eion  ) {
      layerLocalPoint += step * theCrossGap->unitVector(); // local point where the collision occurs
      ionize( eloss, layerLocalPoint );
    }
    else {
      LogTrace(me) << "Energy available = " << eloss <<
        ", too low for ionization.";
    }

  } // step/collision loop

  //TODO port this
  //if ( debugV ) writeSummary( n_steps, sum_steps, dedx, simHit.energyLoss() );

  // Return values in two container arguments
  positions = theCrossGap->ionClusters();
  electrons = theCrossGap->electrons();
  return;
}

double CSCGasCollisions::generateStep( double avCollisions ) const
{
// Generate a m.f.p.  (1/avCollisions = cm/collision)
  double step = (theRandExponential->fire())/avCollisions;

// Without using CLHEP: approx random exponential by...
//    double da = double(rand())/double(RAND_MAX);
//    double step = -log(1.-da)/avCollisions;

    LogTrace(me)  << " step = " << step;
    // Next line only used to fill a container of 'step's for later diagnostic dumps
    //if ( debugV ) theCrossGap->addStep( step );
    return step;
}

float CSCGasCollisions::generateEnergyLoss( double avCollisions,
   double anmin, double anmax, const std::vector<float>& collisions ) const
{
// Generate a no. of collisions between collisions[0] and [N_ENERGY-1]
    float lnColl = log(theRandFlat->fire(anmin, anmax));

// Without using CLHEP: approx random between anmin and anmax
//    double ra = double(rand())/double(RAND_MAX)*avCollisions;
//    cout << "ra = " << ra << std::endl;
//    float lnColl = static_cast<float>( log( ra ) );

    // Find energy loss for that number
    float lnE    = lnEnergyLoss( lnColl, collisions );
    float eloss  = exp(lnE);
    // Compensate if gamma was actually below 1.1
    if ( theCrossGap->gamma() < 1.1 ) eloss = eloss * 0.173554/theCrossGap->beta2();
    LogTrace(me) << "eloss = " << eloss;
    // Next line only used to fill container of eloss's for later diagnostic dumps
    // if ( debugV ) theCrossGap->addEloss( eloss );
    return eloss;
}

void  CSCGasCollisions::ionize( double energyAvailable, LocalPoint startHere ) const
{
  while ( energyAvailable > eion ) {
    LogTrace(me) << "     NEW CLUSTER " << theCrossGap->noOfClusters() + 1 <<
           " AT " << startHere;
    LocalPoint newCluster( startHere );
    theCrossGap->addCluster(newCluster);

  //@@ I consider NOT subtracting eion before calculating range to be a bug.
  //@@ But this changes tuning of the algorithm so leave it until after the big rush to 7_5_0
  //@@  energyAvailable -= eion; 

  // Sauli CERN 77-09: delta e range with E in MeV (Sauli references Kobetich & Katz 1968,
  // but I cannot find this expression in that set of papers.)
  // Take HALF that range. //@@ Why? Why not...
    double range = 0.5 * (0.71/gasDensity)*pow( energyAvailable*1.E-6, 1.72);
    LogTrace(me) << " range = " << range;
    if ( range < clusterExtent ) {

      // short-range delta e
          // How many electrons can we make? Now use *average* energy for ionization (not *minimum*)
      int nelec = static_cast<int>(energyAvailable/ework);
      LogTrace(me) << "s-r delta energy in = " << energyAvailable;
      //energyAvailable -= nelec*(energyAvailable/ework);
      energyAvailable -= nelec*ework;
        // If still above eion (minimum, not average) add one more e
      if ( energyAvailable > eion ) {
        ++nelec;
        energyAvailable -= eion;
      }
      LogTrace(me) << "s-r delta energy out = " << energyAvailable << ", nelec = " << nelec;
      theCrossGap->addElectrons( nelec );
      break;

     }
     else {
      // long-range delta e
         LogTrace(me) << "l-r delta \n"
             << "no. of electrons in cluster now = " << theCrossGap->noOfElectrons();
         theCrossGap->addElectrons( 1 ); // Position is at startHere still

          bool new_range = false;
          while ( !new_range && (energyAvailable>ework) ) {
            energyAvailable -= ework;
            while ( energyAvailable > eion ) {
              double range2 = 0.5 * 0.71/gasDensity*pow( 1.E-6*energyAvailable, 1.72);
              double drange = range - range2;
              LogTrace(me) << "  energy left = " << energyAvailable << 
                        ", range2 = " << range2 << ", drange = " << drange;
              if ( drange < clusterExtent ) {
                theCrossGap->addElectronToBack(); // increment last element
              }
              else {
                startHere += drange*theCrossGap->unitVector(); // update delta e start position
                range = range2;                       // update range
                new_range = true;                     // Test range again
                LogTrace(me) << "reset range to range2 and iterate";
              }
              break; // out of inner while energyAvailable>eion

            } // inner while energyAvailable>eion

          } // while !new_range && energyAvailable>ework

      // energyAvailable now less than ework, but still may be over eion...add an e
          if ( energyAvailable > eion ) {
            energyAvailable -= ework; // yes, it may go negative
            theCrossGap->addElectronToBack(); // add one more e
          }

        } // if range

      } // outer while energyAvailable>eion
}

void CSCGasCollisions::writeSummary( int n_steps, double sum_steps, float dedx, float simHiteloss ) const
{
  std::vector<LocalPoint> ion_clusters = theCrossGap->ionClusters();
  std::vector<int> electrons             = theCrossGap->electrons();
  std::vector<float> elosses             = theCrossGap->eLossPerStep();
  std::vector<double> steps              = theCrossGap->stepLengths();

    cout << "------------------" << std::endl;
    cout << "AFTER CROSSING GAP" << std::endl;
    cout << "No. of steps = " << n_steps << std::endl;
    cout << "Check:  stored steps = " << theCrossGap->noOfSteps() << std::endl;

    cout << "Lengths of steps: " << std::endl;
    std::copy( steps.begin(), steps.end(), std::ostream_iterator<float>(cout,"\n"));
    cout << std::endl;

    if ( saveGasCollisions ) {
      ofstream of0("osteplen.dat",ios::app);
      std::copy( steps.begin(), steps.end(), std::ostream_iterator<float>(of0,"\n"));
    }

    cout << "Total sum of steps = " << sum_steps << std::endl;
    if ( n_steps > 0 ) cout << "Average step length = " << 
       sum_steps/float(n_steps) << std::endl;
    cout << std::endl;
    
    cout << "Energy loss per collision:" << std::endl;
    std::copy( elosses.begin(), elosses.end(), std::ostream_iterator<float>(cout,"\n"));
    cout << std::endl;

    if ( saveGasCollisions ) {
      ofstream of1("olperc.dat",ios::app);
      std::copy( elosses.begin(), elosses.end(), std::ostream_iterator<float>(of1,"\n"));
    }

    cout << "Total energy loss across gap = " << dedx << " eV = " <<
       dedx/1000. << " keV" << std::endl;
    int n_ic = count_if( elosses.begin(), elosses.end(),
                     bind2nd(greater<float>(), eion) );
    cout << "No. of primary ionizing collisions across gap = " << n_ic << std::endl;
    if ( n_steps > 0 ) cout << "Average energy loss/collision = " << 
       dedx/float(n_steps) << " eV" << std::endl;
    cout << std::endl;

    cout << "No. of ion clusters = " << ion_clusters.size() << std::endl;
    cout << "Positions of clusters:" << std::endl;
    std::copy( ion_clusters.begin(), ion_clusters.end(), 
         std::ostream_iterator<LocalPoint>(cout,"\n"));
    cout << std::endl;

    if ( saveGasCollisions ) {
      ofstream of2("oclpos.dat",ios::app);
      std::copy( ion_clusters.begin(), ion_clusters.end(), 
         std::ostream_iterator<LocalPoint>(of2,"\n"));
    }

    cout << "No. of electrons per cluster:" << std::endl;
    std::copy( electrons.begin(), electrons.end(), std::ostream_iterator<int>(cout,"\n"));
    cout << std::endl;

    if ( saveGasCollisions ) {
      ofstream of3("oepercl.dat",ios::app);
      std::copy( electrons.begin(), electrons.end(), std::ostream_iterator<int>(of3,"\n"));
    }

    // Check for zero-e clusters
    std::vector<int>::const_iterator bigger = find(electrons.begin(),
           electrons.end(), 0 );
    if ( bigger != electrons.end() ) {
       cout << "Error! There is a cluster with 0 electrons." << std::endl;
    }
    int n_e = accumulate(electrons.begin(), electrons.end(), 0 );
    if ( n_steps > 0 ) {
      cout << "#        cm       cm             keV               eV          eV       eV     keV" << std::endl;
      cout << " " << n_steps << "  " << sum_steps << " " << sum_steps/float(n_steps) << "    " <<
         ion_clusters.size() << "    " <<
         dedx/1000. << "    " << n_ic << "    " << dedx/float(n_steps) << "  " << n_e << "  " <<
         dedx/float(n_e) << " " << float(n_e)/float(ion_clusters.size()) << " " << simHiteloss*1.E6 << std::endl;
    }
}

float CSCGasCollisions::lnEnergyLoss( float lnCollisions, 
   const std::vector<float>& collisions ) const {

  float lnE = -1.;

   // Find collision[] bin in which lnCollisions falls
    std::vector<float>::const_iterator it = find(collisions.begin(),
      collisions.end(), lnCollisions );

    if ( it != collisions.end() ) {
      // found the value
      std::vector<float>::difference_type ihi = it - collisions.begin();
      LogTrace(me) << ": using one energy bin " << ihi << " = " 
                         << theEnergyBins[ihi]
                 << " for lnCollisions = " << lnCollisions;
      lnE = theEnergyBins[ihi];
    }
    else {
      // interpolate the value
      std::vector<float>::const_iterator loside = find_if(collisions.begin(),
        collisions.end(), bind2nd(less<float>(), lnCollisions));
      std::vector<float>::difference_type ilo = loside - collisions.begin();
      if ( ilo > 0 ) {
        LogTrace(me) << ": using energy bin " 
                           << ilo-1 << " and " << ilo;
        lnE = theEnergyBins[ilo-1] + (lnCollisions-collisions[ilo-1])*
          (theEnergyBins[ilo]-theEnergyBins[ilo-1]) /
             (collisions[ilo]-collisions[ilo-1]);
      }
      else {
        LogTrace(me) << ": using one energy bin 0 = " 
                           << theEnergyBins[0]
               << " for lnCollisions = " << lnCollisions;
        lnE = theEnergyBins[0]; //@@ WHAT ELSE TO DO?
      }
    }

    return lnE;
}

void CSCGasCollisions::fillCollisionsForThisGamma( float logGamma,
   std::vector<float>& collisions ) const
{
  std::vector<float>::const_iterator bigger = find_if(theGammaBins.begin(),
    theGammaBins.end(), bind2nd(greater<float>(), logGamma));

  if ( bigger == theGammaBins.end() ) {
    // use highest bin
    LogTrace(me) << ": using highest gamma bin" 
              << " for logGamma = " << logGamma;
    for (int i=0; i<N_ENERGY; ++i)
      collisions[i] = theCollisionTable[i*N_GAMMA];
  }
  else {
    // use bigger and its lower neighbour
    std::vector<float>::difference_type ihi = bigger - theGammaBins.begin();
    if ( ihi > 0 ) {
      double dlg2 = *bigger--; // and decrement after deref
      //LogTrace(me) << ": using gamma bins " 
      //                   << ihi-1 << " and " << ihi;
      double dlg1 = *bigger;   // now the preceding element
      double dlg = (logGamma-dlg1)/(dlg2-dlg1);
      double omdlg = 1. - dlg;
      for (int i=0; i<N_ENERGY; ++i)
        collisions[i] = theCollisionTable[i*N_GAMMA+ihi-1]*omdlg +
          theCollisionTable[i*N_GAMMA+ihi]*dlg;
    }
    else {
      // bigger has no lower neighbour
       LogTrace(me) << ": using lowest gamma bin" 
                     << " for logGamma = " << logGamma;

      for (int i=0; i<N_ENERGY; ++i)
        collisions[i] = theCollisionTable[i*N_GAMMA];
    }
  }
}